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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Fri Aug 04, 2017 4:02 pm 



Joined: 03 Mar 2005
Posts: 231
Thank you very much. That's interesting to look at.

The main oscillator is not a UPC1883, but a TDA4856. Made by Phillips, not NEC.

http://pdf.datasheetcatalog.com/datashe ... 4856_2.pdf

EDIT: Scratch that, maybe it does have an AFC-like function.

More tomorrow. I've been learning a lot of new things. I might actually have to buy a logic analyzer now...


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Sat Aug 05, 2017 4:38 am 



Joined: 02 Mar 2017
Posts: 180
An update to VCR Mode on a Sony BVM-D14(and I assume the D9 as well), but like the manual says, these units DO have VCR Mode, and it's able to be turned on, but ONLY with the Composite/S-Video (Y/C) BKM-127W input card (thank you to lewolfeur for this revelation).

I wonder how we could make VCR Mode accessible for RGB sources using the more common BKM-129x card? Any ideas?


Update on the Raspberry Pi 3 RetroTINK-RGB board by Mike Chi (posted with his permission) in regards to sync:

“””I use a XNOR gate to combine the horizontal and vertical syncs. The output does contain horizontal slices in the vertical sync but it's not 100% to spec since there it causes a slight time shift in the horizontal sync during the vertical sync period. This causes the AFC PLL to have to re-lock at the start of every new screen refresh.

For my PVM and BVM, this results in that dampened oscillation like in the figures you [I sent him the link to the RetroRGB site about AFC and the 68x card) sent but by the time it gets to the active image area it's fine. One user had a BVM-D20F1U that didn't behave until he turned on VCR mode but it sounds like you don't have that option.

I think the safest choice is to use a modified RetroTINK-RGB where I modify the device to output a pure HSYNC (instead of CSYNC). You could combine the HSYNC and VSYNC lines by connecting them to the sync input and output lines of your BVM (don't worry it sounds weird but that's what I do for my BVM). That would preserve the correct HSYNC information during the VSYNC period.”””

So I bought his board and am going to see if it fixes my problem as ideally I bought the BVM-D9 specifically for a RetroPie project. I’ll report back with if this worked.


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Mon Aug 07, 2017 12:49 pm 



Joined: 18 May 2017
Posts: 26
Location: Montpellier, FRANCE
I was contacted by a french person of ikegami, he want i give him all information, description, diagram of the connection to monitor. (maybe there already in the beginning of this topic)
He will try to transfer it to an old ingeneer of ikegami (if there still one) for know if there is a possibility of modification for this sync issue .


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Tue Aug 08, 2017 1:45 am 



Joined: 03 Mar 2005
Posts: 231
lewolfeur wrote:
I was contacted by a french person of ikegami, he want i give him all information, description, diagram of the connection to monitor. (maybe there already in the beginning of this topic)
He will try to transfer it to an old ingeneer of ikegami (if there still one) for know if there is a possibility of modification for this sync issue .


Wow.

I would be happy to make a detailed summary of the situation, and to provide all documentation. You could send it to the French Ikegami representative.

Would the old Ikegami engineer be Japanese? If so, I could write to him directly in Japanese.

For now, I will start preparing the documentation.


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Tue Aug 08, 2017 9:59 am 



Joined: 03 Mar 2005
Posts: 231
I have made many incorrect assumptions. So many, in fact, that I really ought to update the OP.


Having said that, I think I'm beginning to reach an understanding of what's happening here.

The UPC1883 is the heart of the HTM-2050R2's deflection card. It's the IC that takes the sync signals and controls the yoke with them. However, Ikegami did something with it that not only goes against what the datasheet recommends, but defies logic entirely. The only way it makes any sense at all is if Ikegami didn't mark something critical on their schematic...and that's what I currently suspect is exactly what happened. (EDIT: Nope! Seriously, this makes no sense.)

Allow me to explain.


This is a block diagram of the UPC1883, with the bottom cut off since that only deals with vertical sync:



Image



Pin 26 is the input for the sync pulse, and pin 17 is the input for the flyback pulse. As I understand it, AFC in general works by comparing a new and incoming sync pulse with the in-progress flyback pulse to see if there is a difference. A difference indicates that the sync pulse is not in the right place, and the circuit will act to correct it accordingly.

Therefore, the actual comparing happens inside of this UPC1883. This is something I had quite wrong before; I thought that at least part of the AFC process was happening externally, but it's not.

So, what the heck are pin 24, the 4053B "sync selector" and all of the external slow/fast/normal things all about? Contrary to what I thought before, pin 24 is not an input - rather, it is there to output a voltage. It is the modulation of this voltage by an external circuit that determines exactly how the AFC deals with a difference in the sync/flyback pulses.

Let's look at the extra info on pin 24 in the detailed Japanese datasheet.



Image



The circuitry you see here is simply what's inside of the IC. The 3.5V is vaguely the "pin voltage" which I am only realizing now is an output. On the right, where it tells you what to attach to the pin, it says "Construct a lag-lead filter. The time constant of this filter will influence horizontal jitter. Generally, in cases where there is fast, fine jitter, make the time constant long, and in cases where there is large, deep jitter, make the time constant short. However, please consider this only after confirming that there is no jitter component in the signal being input to pin 26."

By the last sentence, I assume that they mean to make sure that your monitor circuitry design itself isn't adding jitter on its own.

This, from the block diagram above, is what they mean when they say a lag-lead filter:



Image



I'm just learning about what these are really all about. You know, they actually mispelled lag lead filter in the datasheet (ラングリード instead of ラグリード) which threw me off the trail since I couldn't google it. Anyway, at last, let's repost that schematic from the previous page and take a look.



Image



You'll notice that there is indeed a 3.3k resistor / 2.2uF capacitor combo just like in the UPC1883 datasheet. This is what they recommend. The other selectable lines have a 3.3k resistor / 1.0uf capacitor and a 2.2k resistor /0.22uf capacitor combo, which must simply give different time constants.

What it looks like is that none of the other crap before this really matters. The 4053B (IC207) is nothing but a group of switches. The NJU3718 is nothing but a switch-flipper, and it's not even the thing that decides which switch to flip - that happens much earlier in the chain, probably by some computer on the motherboard.

The only thing that matters is which resistor/capacitor combo is being used to modulate the output of pin 24 and create a time constant for it. This is where that paragraph Xer Xian posted before applies:

Quote:
The time constant of the RC filter provided at the output of the discriminator, determines how fast the dc control voltage can change its amplitude to correct the oscillator frequency. A time constant much larger than 64 μs is needed for the shunt capacitor to bypass horizontal sync and sawtooth components in the control circuit while filtering out noise pulses. However, a large time constant may not permit the control voltage to change within a fraction of a second when sync is temporarily lost while changing channels. Also, if the time-constant is too large, the dc control voltage may be effected by the vertical sync pulses, causing bend at the top of the picture. A typical value of the AFC filter time-constant is about 0.005 second, i.e., a period nearly equal to 75 horizontal lines.

The filtering circuit that follows the diode section of the discriminator controls the performance of the AFC circuit. Too large a time constant makes the control sluggish, while insufficient damping, on account of too small a time constant, causes the oscillator to ‘hunt’ returning to the correct frequency. Excessive hunting in the AFC circuit appears as ‘weaving’ or ‘geartooth’ on the picture.



Here is what confuses the heck out of me: lag-lead filters are supposed to go to ground. The example diagram here has it going to ground. Meanwhile, the stupid Ikegami schematic has it switching between the 9V power rail and nothing, just an open circuit.

What I suspect is that in the schematic, they neglected to mark that pins 13, 1 and 3 of the 4053B (IC207) go to ground. This is the only way any of this makes sense.

As you can see in this link, 9V at one end of one of these lag-lead filters and 3.5V at the other cause things to come to a stand-still, effectively just turning it off. Therefore, what probably happens is that the NJU3718 only toggles one of these pairs at a time, giving it access to ground, while the other two are negated by the 9V connection.


What I'm going to try next is to simply bypass the 4053B entirely and force specific lag-lead filters on pin 24. One resistor, one capacitor, soldered to pin 24 and ground. Everything else gets cut off.


EDIT: Damn it, pins 1, 3 and 13 really do look like they're floating and not grounded. How the hell is this supposed to work? I found other datasheets for TV oscillators like this, the TA8867AN, the CXA1871S and the NJM2257, and they also have lag-lead filters going to ground. It just doesn't make any sense! Screw it, I'm trying the idea above anyway. All I want to do is try connecting the AFC filter pin like they have in the datasheet. Hopefully nothing will blow up.

CXA1464AS, too.


Last edited by SamIAm on Wed Aug 09, 2017 8:40 am, edited 6 times in total.

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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Tue Aug 08, 2017 12:38 pm 



Joined: 18 May 2017
Posts: 26
Location: Montpellier, FRANCE
SamIAm wrote:
lewolfeur wrote:
I was contacted by a french person of ikegami, he want i give him all information, description, diagram of the connection to monitor. (maybe there already in the beginning of this topic)
He will try to transfer it to an old ingeneer of ikegami (if there still one) for know if there is a possibility of modification for this sync issue .


Wow.

I would be happy to make a detailed summary of the situation, and to provide all documentation. You could send it to the French Ikegami representative.

Would the old Ikegami engineer be Japanese? If so, I could write to him directly in Japanese.

For now, I will start preparing the documentation.


Yes say him that we have some monitor 1990r and 2050 and there is some sync problem with some video game console, he want the diagram of how we connect console to monitor, the console description (it would be best to give him the description of composite sync signal from each console who have problem) In my case only neogeo aes NTSC-J and nintendo 64 PAL. (but i am sure the other console who have problem on 2050 have same problem on 1990r)

Yes the old engineer will must be a japanese or someone who know well these model, dont know if we can have after a direct mail to contact him.

Of course, it guarantees nothing thereafter, the person or persons are likely to see these information, we'll see if that gives some positive things about for us, a mod to do or else.


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Tue Aug 08, 2017 2:46 pm 



Joined: 03 Mar 2005
Posts: 231
Ah, OK. If he said it like that, he might not be able to do much for us. There is a big difference between helping someone connect something properly and set all the right settings, and helping them open the system and modify the way it works. Due to the danger involved, he is probably obligated by company rules not to assist us at all.

But if you're reading this, Ikegami guy, please do help us if you can!


---------------


Image

This is the schematic of the BVM-2015's AFC switch. See where it says AFC.SW and S/N/F? Notice how it has the same lag lead filters set up. In fact, all it does is vary the resistor value.

What I think I'm going to do is connect a lag lead filter like the UPC1883 document says to do, including a 2.2uf capacitor, but to use a potentiometer to try to find the best value possible.


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Tue Aug 08, 2017 5:27 pm 



Joined: 18 May 2017
Posts: 26
Location: Montpellier, FRANCE
Will reply him this friday with the information i have and link to this topic, i you want to send me addition information , because i am not as good to the research like you do in this post, i will add them.

we will see if this result to something.

also pick up 3 day ago a d20f1 and seem like he have a sync issue with neogeo aes, vcr mode to "on" and still same. ( dreamcast 240p test suite worked without sync issue)
https://www.youtube.com/watch?v=a4Pa6U2 ... e=youtu.be


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Wed Aug 09, 2017 1:52 am 



Joined: 03 Mar 2005
Posts: 231
Fascinating development!

Remember how I said I bought a second HTM-2050R2 that turned out to be junk, the seller was going to send me another one, and I would have an expendable unit to experiment on? Well, the other one came. After getting the resistors I took out back on the first unit (no damage done - it works again), I busted open the expendable unit to get the deflection board out.

It was clearly a revised version.

I should note from the beginning that PC Engine video does basically the same thing on this set, although it is slightly different.

Anyway, the 4053B? Gone. The three 2SC3398 transistors? Gone. Every resistor from 267 to 277 and capacitors 242 and 243? Gone, all with nothing to replace them - just empty solder pads. And the connection to the NJU3718? Cut. Literally the only thing left of that entire mess in the schematic I've posted a few times was a single resistor/capacitor combo, connecting to pin 24 and looking just like a lag-lead filter...except that it's still connected to the damn 9V rail and not ground.

I'll take real pictures later, but this is what the revised schematic would look like.

Image



So, why the hell is the resistor/capacitor lag-lead filter connected to 9V and not ground? I don't know, but the next time I have a minute to fool with this, I'm going for the ground connection like in the UPC1883 datasheet.

Wild guess time: Ikegami may have been setting up to allow the user to select slow/normal/fast AFC from within the digital on-screen menu. That would explain why they would involve a digital-signal chip like the NJU3718. Using a 4053B as a switch multiplex makes perfect sense in this case. Then, they probably gave up on it at some point, but left some of the parts on the board (when you're selling a CRT for $10,000+, a few more pennies in parts matters little).

Why on earth they have the filter(s) going to 9V is beyond me. Maybe it's supposed to be like that for a reason I'm not aware of; maybe it's just a mistake that didn't cause any problems. But since the PC Engine video is equally messed up on this board, I strongly suspect that this AFC filter function is and has always been improperly implemented.

I can't wait to try fixing it!

EDIT: Nope! I'm wrong again. It turns out that you can have 9V at the other end of the capacitor and it will work.

It sounds like these lag-lead filters involve simply charging a capacitor, then discharging it in the opposite direction. When it finishes charging and discharging is based on how large the capacitor is, and how much resistance is between it and the voltage source.

Link to simulated circuit.


Last edited by SamIAm on Wed Aug 09, 2017 9:52 am, edited 1 time in total.

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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Wed Aug 09, 2017 8:09 am 


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Joined: 06 Feb 2005
Posts: 244
Location: Italy
SamIAm wrote:
Wild guess time: Ikegami may have been setting up to allow the user to select slow/normal/fast AFC from within the digital on-screen menu. That would explain why they would involve a digital-signal chip like the NJU3718. Using a 4053B as a switch multiplex makes perfect sense in this case. Then, they probably gave up on it at some point, but left some of the parts on the board (when you're selling a CRT for $10,000+, a few more pennies in parts matters little).

Makes sense to me. Also, that was some good reverse-engineering, figuring out about the UPC1883 and the IC207 roles (or lack thereof)! This thread, with all the twists and revelations, feels like reading a crime novel - I'm loving it :D


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Wed Aug 09, 2017 9:10 am 



Joined: 03 Mar 2005
Posts: 231
Xer Xian wrote:
SamIAm wrote:
Wild guess time: Ikegami may have been setting up to allow the user to select slow/normal/fast AFC from within the digital on-screen menu. That would explain why they would involve a digital-signal chip like the NJU3718. Using a 4053B as a switch multiplex makes perfect sense in this case. Then, they probably gave up on it at some point, but left some of the parts on the board (when you're selling a CRT for $10,000+, a few more pennies in parts matters little).

Makes sense to me. Also, that was some good reverse-engineering, figuring out about the UPC1883 and the IC207 roles (or lack thereof)! This thread, with all the twists and revelations, feels like reading a crime novel - I'm loving it :D


I'm glad I'm not just annoying people with all of these posts. It helps me think to lay out everything and have to explain it. :D

--------------------------------

Here's another link to the same set of simulated circuits as before, with minor modifications. If you're wondering what a time-constant can do, not so much what it is, this can help fill you in. On the far right oscilloscope, you'll see a pure pulse, while on the other four, you'll see the pulse get stretched by varying speeds and amplitudes of capacitor discharge. There is a slider on the right that will let you adjust the resistor on the bottom circuit. Notice how a 1uf capacitor discharging through a 3.3k resistor has a similar profile to a 2.2uf capacitor discharging through a 1.2k resistor.

Recall that the junk unit has only a 3.3k resistor and a 2.2uf capacitor as a lag-lead filter on pin 24. This is the same as the slowest of the three speeds on my original HTM-2050R2. Slow means a long time constant. The UPC1883 datasheet said "In cases where there is large, deep jitter, make the time constant short." The extreme warping of the PC Engine picture suggests that we need to make the time constant shorter, which means that I should replace the junk unit's 3.3k resistor with something like a 1.2k resistor.

By the way, I think that my previous experiment with taking other resistors off resulted in pin 24 of the UPC1883 getting no lag-lead filter at all. That would explain why the result was so drastically bad.

So, a shorter time constant seems like the best idea to start with. However, it's possible that the solution will be much the reverse of that. Take a look at this excerpt about "hunting". Even if you don't read the text, just look at the graph. This is illustrating what happens when the time constant is too short: basically, the AFC circuit winds up overcorrecting any problems. See how it looks like it would result in a picture that waves back and forth repeatedly? Well, that is exactly the kind of distortion that I see in the PC Engine video.

Image

An entire pulse missing and an over-agressive correction would explain why the picture is bad for the entire top third of the screen.

Thus, today I bought a 10k potentiometer. I plan on taking out the 3.3k resistor in the junk unit, running long wires between the solder pads and a breadboard with this potentiometer on it, and while wearing PVC gloves, I'm going to try adjusting the resistance while the unit is on. Don't worry, this is all pretty low-voltage.

If turning the resistance down below 3.3k improves the picture, then we know that the time constant before was too long. However, if turning it down makes the problem worse, and/or if turning it up makes it better, then it's this hunting that's the problem, , and I think...

Image

...that that might mean toying with this dinky little 0.001uf capacitor. EDIT: I can't help but notice that most other oscillator datasheets that designate a filter like this one have that little cap as 0.01uf...


If you want to know what a time constant really is, take a look at this RC time constant calculator.

Quote:
If a voltage is applied to a capacitor of Value C through a resistance of value R, the voltage across the capacitor rises slowly. The time constant is defined as the time it will take to charge to 63.21% of the final voltage value.


Now, look at the example time constant filter in that excerpt: 1m resistor with a 0.005uf capacitor. Run this through the calculator, and you get a time constant 0.005 seconds, just like they said. 3.3k and 2.2uf is 0.007 seconds, or 7ms.

My BVM's slow AFC setting is 7ms. Normal is 2ms, and fast is 0.5ms. If I use the 2.2uf capacitor, that means I need a 1k resistor for 2ms. The lowest I can get with this capacitor seems to be 1ms, which I can do with 500 ohms.


EDIT: Sigh. On my junk unit, one of the screws that held the deflection board's heat sink to the main chassis was badly stuck, and I had to chisel it. I did the mod on the board...now the system won't turn on. I didn't have time to look into it, but I think the power board got rattled in the process since it's right behind where I was hitting. Here's hoping it's just something mundane like a connector that got knocked loose.

If it's really dead, then hey, at least it was the junk unit.

EDIT2: What am I thinking? Too much hunting would result in every sequential line being alternately left or right of where it should be. What I'm seeing is collections of lines making large wave patterns. It's definitely not over-hunting. It's probably not enough hunting. If I can get my stupid junk unit to come back on, I'm going right for smaller resistance values.


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Fri Aug 11, 2017 12:50 am 



Joined: 03 Mar 2005
Posts: 231
It was a day of successes and defeats.

First, as I mentioned in an edit above, I had a tough time getting a screw out of my junk 2050. It was holding the deflection board in place, so I had to get it. The head got totally stripped, and in the end, there was nothing but to chisel the thing. It came out, but the next time I tried to turn on the system, it gave no sign of life. I checked the fuse and many other things on the power board, which were all near the screw and took a relatively high amount of shock from the chiseling, but there is no sign of trouble. Meanwhile, when I plug it in and turn it on, none of the test-points for any of the voltages give anything, even for a moment.

Thus went the first defeat. At least it was the junk unit.

I took the simplified deflection board from the junk unit and quickly modified it so that it would have a 10k pot in place of the 3.3k resistor and connected it with wires so that I could adjust the pot in real-time with the TV on. Luckily, this board is fully compatible with the good units, and it still works.

Unlike last time, where my experiment caused total chaos on the screen, this functioned. Set to about 3.3k, the pot gave the same results as I always get, and adjusting it, I could see changes. Just the fact that I've come this far - I've understood what time-constants in AFC are about, and I've successfully implemented the mod I've always wanted to try - was very gratifying. It feels like a success.

That's why it doesn't bother me terribly that it didn't fix the problem with PCE video. Reducing the resistance and shortening the time constant moved the distortion up the screen a little, but it far from fixed it.

Image

This is pretty much what it's always looked like.

Increasing the resistance didn't really hurt at first, but at the full 10k, the whole picture started wobbling a little.

I also tried the SFC to see if the jitter in the top few lines could be removed by adjusting the AFC here, but it couldn't. That's a little more disappointing, to be honest.

In terms of what else might be tried, there are two things: 1. Swap the 2.2uf capacitor with something smaller. This would give the time constant pulses a different shape (not sure if that matters) and allow me to push for shorter constants than the 2.2uf cap allows. 2. Swap the 0.001uf capacitor with something larger. No idea what this will even do (my money is on nothing at all), but I'm just curious since so many other designs use a 0.01uf capacitor.

On the other hand, I've got all the parts to try the mod I linked to before that will take the raw Hsync and Vsync pulses from the PC Engine and reshape them, then mux them together. I'm a lot more optimistic about getting that to work.

There are also the Extrons...but I'm not as hopeful about them. Adding an altogether missing pulse seems beyond what these were designed to do.

No matter what happens with this current mod...even it it turns out that dealing with a missing pulse beyond what the oscillator in the HTM-2050R2 is capable of even with the AFC adjusted...at least we'll know for sure. That's a good enough result for me!


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Fri Aug 11, 2017 2:52 pm 



Joined: 04 Jun 2015
Posts: 117
Keen to see how you progress with this, SamIam.

I was having a look at one of my old TV repair books and found a section on AFC modifications for TV's. I'm not sure if it will help you or not but thought I would post the info in case it does. The important part to note is the author recommends reducing the value of the capacitor(s) in the anti-hunt network to shorten the time constant.

Image

Image


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Sat Aug 12, 2017 5:20 pm 



Joined: 03 Mar 2005
Posts: 231
@xga - Thank you so much for taking the time to get those scans to me. :)

I recently did the following:

1. Tried replacing the 0.001uf cap with a 0.01uf cap. It only screwed up the picture. Interestingly, leaving it off altogether didn't cause any noticeable effects until I switched the unit in and out of the on-board HD test patterns. After that, the oscillator somehow stretched the 240p image 2x vertically!

2. Tried swapping the 2.2uf cap in the main RC time-constant filter with a 0.22uf cap. Although I was able to push the constant shorter than before, it didn't help much at all.

I'd be happy to try some things with an anti-hunt circuit added to the main filter, except that I don't feel like I really understand how it works or how it's supposed to be implemented.


Instead, I just had a crazy thought, and if someone thinks it's incredibly bad, please shoot it down.

Let's look at this summary of what AFC is, and what is implicitly coming out of pin 24 on the UPC1883.

Quote:
[AFC] detects the difference in frequency [between the sync pulse and the flyback pulse] and develops a dc output voltage proportional to the difference in frequency between the two input voltages. The dc control voltage indicates whether the oscillator is ‘on’ or ‘off ’ the sync frequency. The greater the difference between the correct sync frequency and the oscillator frequency, larger is the dc control voltage. This dc control voltage is fed to a large time constant filter [at pin 24], the output of which is used to control the oscillator frequency.


What this should mean is that when there is an altogether missing pulse, there should be an uncommonly enormous voltage generated at pin 24. It should be far, far greater in size than any voltage developed by a slightly mistimed pulse, or an extra pulse caused by noise. On an oscilloscope, it should show up as a great peak, followed in this case by smaller and smaller peaks as the UPC1883 finds its way back to the proper timing.

My crazy idea is, what if I just clamped this voltage with a zener diode?

It would require getting an oscilloscope to see what the real voltages are, but it seems to me that if I can clip this first giant voltage spike caused by the missing pulse, it should make it much easier and faster for the system to get back to its proper state.

Thoughts?


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Sun Aug 13, 2017 12:06 am 



Joined: 18 May 2017
Posts: 26
Location: Montpellier, FRANCE
there my test with my multiformat (dt-v1900cg, d20f1,1990r)
http://imgur.com/a/YTTZI

its not help but just a comparison to add.


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Wed Aug 16, 2017 6:16 pm 



Joined: 18 May 2017
Posts: 26
Location: Montpellier, FRANCE
here the first reply from french ikegami branch : (Hope the translation is good)

Quote:
Information taken, the sync input of the monitor must receive a composite sync signal (csync) and only that. These monitors are initially intended for professional use (broadcast) and therefore to receive the signals used in this type of environment (RGB + S).

Consoles that do not provide a sync signal must go through a sync separator that will remove the video from the composite video signal (CVBS) to keep only the H & V sync (csync).


The *competing monitors that apparently accept the CVBS signals on the sync input must in fact already have a sync separator on that same input.
Again, this conversion is not necessary when working in a professional environment, since a dedicated black burst signal is used.


But for my case i already use a gscartsw v3.4 (csync "on"), so still a problem with my french n64 and aes.
*(Competing monitor are dt-v and bvm-d).


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 Post subject: Re: Wonky sync, AFC, and an Ikegami HTM-2050R2: Help wanted
PostPosted: Thu Aug 17, 2017 3:22 am 



Joined: 03 Mar 2005
Posts: 231
Well, thanks for taking the time to contact them. :)

The HTM-2050R2 takes composite video as sync with no problem. That's what I use with multiple other consoles, and it works fine. I've also used an LM1881 to change the PCE composite video to CSYNC with no effect on the result.

If I run out of ideas, maybe I'll try contacting NEC about the UPC1883.

----------------------

I've started looking at used oscilloscopes on Yahoo Auctions. In the meantime, it's finally time to try my next experiment.

Since it turned out that using a shorter time constant barely changes anything, my new hope is that I can do something else externally at the UPC1883.

Based on the descriptions of AFC that I've read, it looks like the missing pulse could result in the capacitor at pin 24 getting a relatively large, high voltage charge. My new theory is that it's the release of this charge that's screwing things up. Thus, I'm curious about what will happen if I use a diode, or multiple diodes, to short higher voltages to ground and prevent that charge from building. At its most rudimentary, the new circuit would look like this:

Image

Silicon diodes have a characteristic that they don't turn on and allow current to flow until a certain minimum voltage is reached - typically, this is listed as 0.7V. Low amounts of current can be passed at as little as 0.4V, however, and quite a lot can pass at 0.6V.

The arrangement above should result in <0.4V charges to the capacitor being completely unaffected, and >0.6V charges being completely clipped.

0.4V is not very much, so I'm going to keep a bunch of diodes handy so I can stack them. Two diodes in a row should result in the same thing as above except with the numbers being <0.8V and >1.2V. Three would be <1.2V and >1.8V, etc. By mixing in germanium diodes, which fully conduct at 0.3V, I could adjust in even smaller increments. Also, by putting a resistor between the diodes and ground, I could attenuate the clipping.

Current, at least, should be plenty limited by the 1.2k resistor.

Also, I just learned something important: the voltage at pin 24 might be negative during this missing-pulse area.
Quote:


Without an oscilloscope, I have no way of knowing what's really going on with this thing, but the diode solution could still work with a negative voltage. All that's necessary is turning the diodes around.

Here is another link to a pair of simulated circuits, with the difference being the number of diodes in series. You can easily flip switches and adjust potentiometers to control the attenuation of the wave. In addition, if you edit the voltage level of the source (where it says 20Hz) you can see how the diodes don't do anything to low-voltages.

This is all admittedly a shot in the dark, but for the time being, it seems the most reasonable thing to try to me.


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