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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Wed Aug 17, 2016 11:45 pm 



Joined: 13 Jul 2016
Posts: 48
xga wrote:
No worries, mate. I'm sure that we'll get to the bottom of the issue soon.

I actually have one of those RGB bypass boards for a Megadrive minus the components. I never got around to ordering the parts for it. Instead I'm waiting for when these become available for sale - https://vmod.wordpress.com/megamod-v3-0/.


Update: My Neo Geo cable from retrogaming cables arrived today, I've been testing it in my Sony Trinitron CRT, perfect picture, no flaws. I've tested it again on my BVM-A20F1M and got image distortion, this time the games are actually playable, but the image is skewed to the right as seen in the picture.

Image


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Thu Aug 18, 2016 1:21 am 



Joined: 18 Aug 2016
Posts: 1
I'll start by saying I know nothing about electical, wiring, or even how to solder. But I did have this problem with my Dreamcast to my BVM and it was serration pulses. I only know that because I have it running through an Extron RGB-192 and I had that same issue untill I flipped the dip switch for serration pulses.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Aug 23, 2016 11:20 pm 



Joined: 13 Jul 2016
Posts: 48
Could someone else with a BVM-A20F1M please report their results? What kind of consoles are you using your monitor with?


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Aug 30, 2016 7:41 pm 



Joined: 13 Jul 2016
Posts: 48
I've tried with an RGB moded NTSC NES, the BVM works well.

The incompatibility seems to affect only the SEGA consoles and the Neo Geo.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Oct 25, 2016 2:30 pm 



Joined: 04 Jun 2015
Posts: 115
osarion wrote:
I'll start by saying I know nothing about electical, wiring, or even how to solder. But I did have this problem with my Dreamcast to my BVM and it was serration pulses. I only know that because I have it running through an Extron RGB-192 and I had that same issue untill I flipped the dip switch for serration pulses.


So I've just run my JAP Neo Geo AES through to my A20F1 BVM using a retrogamingcables.co.uk SCART RGB cable and I'm seeing the same issue as PeterWar has shown in the image above. I've also tried running it through my Extron RGB 201 Rxi and turned the serration pulses dip switch on and off and it makes no difference to the image. I've also entered the maintenance menu of the A20F1 BVM, selected the BKM-68X input board and tried testing the various options that are listed within the menu with no difference.

Connecting it over to a D series BVM displays no issues at all and the image is perfect.

I'm running out of things to try to get this to work on the A20F1 with the BKM-68X input board. Can anyone suggest anything else to try, please?


Last edited by xga on Tue Nov 01, 2016 9:33 am, edited 1 time in total.

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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Oct 25, 2016 4:27 pm 


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Location: Germany
If you replace the AES' crystal to make it run closer to NTSC specs, it would probably be fine. You either use a fixed frequency clock or use a programmable one like on the DFO: http://nfggames.com/forum2/index.php?topic=5744.0


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Oct 25, 2016 8:03 pm 


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The megadrive sync should be properly buffered, no wacky RC stuff should be needed. Just about any CMOS 74' chip will do the job (I have a lot of 74HC04 inverters lying around, so I'll just pass it through two inverter gates as a buffer).

Image


Last edited by mikejmoffitt on Tue Nov 01, 2016 7:32 pm, edited 1 time in total.

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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Wed Oct 26, 2016 12:43 pm 



Joined: 07 Aug 2006
Posts: 418
Location: Sydney, Australia
A week or so ago somebody asked me wy why his NES (NESRGB) sync signal did not work with his monitor. He have the model as SONY PVM 14N6U and I was able to find the service manual with a quick web search. The sync input was not well specified, I had to refer to the schematic to find out the input impedance.

Image

4 Vpp +3 dB, -6 dB. In other words the sync signal must be between 5 Vpp and 2 Vpp in amplitude. The tricky part (which isn't even mentioned on the page) is that this is 75 ohm input. The high Vpp requirement makes it icncompatible with an standard 75 ohm sync/video signal (which is typically 0.3 Vpp) and the low impedance of 75 ohms makes it incompatible with a TTL sync signal (which generally want an input impedance > 2000 ohms).

The reason the NESRGB's sync signal didn't work is it has an internal resistor in series with the sync output. The value is high enough to prevents overdriving a standard 75 ohm input, but low enough to maintain compatibility with TTL inputs. I didn't count on a sync input which requires TTL voltage levels with a 75 ohm input impedance.

I don't know about the particular model in the subject of this thread, but it wouldn't surprise me it if was the same. A check with an multimeter will tell the value of the resistor on the input at least.



Image

Connecting the Mega Drive like this will not work because the the pull up strength of the TTL sync signal is a weak 2.2k resistor to the 5V power rail. TTL signals can usually sink more current than they source, but a low impedance (75 ohms) sync imput requires an output that can source a lot of current.



Image

There are two ways to deal with this to make the TTL sync signal from the NESRGB or Mega Drive compatible with this monitor. The first is to install a stronger drive circuit inside the Mega Drive console. This will work, but may have unintended side effects. If there is an aduio signal going through the same cable as well as video, the voltage and current (as high as the R + G + B combined!) of the new sync signal will likely couple into the video unless the cable is of exceptionally high quality.



Image

The other way to solve the problem is to place a cync seperator circuit before the monitor's sync input. This way the monitor now has a standard 75 ohm sync input (like composte video, luma, etc).

To make the Sega's TTL sync signal compatible with this, it needs a passive converter circuit. It's usually possible to convert any TTL sync signal to work with a 75 ohm video/sync line, but the exact components depend on the TTL side. In this case it requires a 470 ohm resistor and large capacitor 220u. The resistor must be placed closed to the source. Either in the cosole or the console end of the cable.

This may seem like an overly complex solution to the problem, but it is really the best one. This way if you replace the monitor, you don't have to change anything regarding you cables. If you get a new console, you can use a standard SCART cable.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Wed Oct 26, 2016 5:46 pm 


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Joined: 06 Mar 2006
Posts: 10445
Location: Germany
great information (and as usual so well documented). I'm wondering to which prof. displays this applies other than this model? After all MOST people using PVM or BVM displays haven't run into these kinds of problems.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Fri Oct 28, 2016 4:25 pm 



Joined: 04 Jun 2015
Posts: 115
Hey Guys, I'm really grateful and appreciative of this further information that you've all provided. Gives me a few more options to explore to try and get this working with the Mega Drive and Neo Geo AES.

@viletim, I've tried to determine the same sync details you mentioned with the PVM-14N6U on my BVM-A20F1A monitor. This monitor does not come standard with analogue inputs, you had to option it with the BKM-68X analogue input board, hence looking in the BVM-A20F1A manual doesn't provide any meaningful information, you have to refer to the BKM-68X operation manual (found here - http://www.embraceit.com.au/bkm-68x/BKM-68X_operationmanual.pdf) and service manual (found here - http://www.embraceit.com.au/bkm-68x/BKM-68X_SM.pdf) instead.



Standard RGBS inputs and outputs on the BKM-68X input board

Image



EXT SYNC is 0.3 to 4 Vp-p

Image



This block diagram has connector CN700 as the HS (presumably Horizontal Sync) input and I thought CN701 should be the sync output, but it is listed as VS (presumably Vertical Sync) input???

Image



Resistor R702 for EXT SYNC?

Image



Where the F&*! is R702 on the parts list??

Image



The Vp-p for the EXT SYNC is 0.3 to 4.

R702 in the schematic appears to be the resistor used for EXT SYNC input. Unfortunately, referring to the parts section, R702 is skipped for some reason (they list the values of R701 and R703). Using a multimeter on the EXT SYNC input BNC connector reveals 76.1 Ohms (close enough to 75).

Does this information point to some sort of incompatibility with the EXT SYNC input like you found with the PVM-14N6U and if so, is the third option you have suggested still the preferred solution in this instance?

Thanks in advance for any further assistance.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Nov 01, 2016 9:12 am 



Joined: 04 Jun 2015
Posts: 115
mikejmoffitt wrote:
The megadrive sync should be properly buffered, no wacky RC stuff should be needed. Just about any CMOS 74' chip will do the job (I have a lot of 74HC04 inverters lying around, so I'll just pass it through two inverter gates as a buffer).

Image


So I tried this circuit with the 74HC04 inverter IC on both my A20F1 and a D14H1 BVM's and I could not get it to work on either of them. I verified that the inverter IC was receiving 5volts from the console. I'm providing sync via the composite video as sync pin from the console. Is this OK or do I need to provide sync from the csync pin?


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Nov 01, 2016 7:29 pm 


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Joined: 08 Jan 2016
Posts: 275
Location: San Jose, CA
xga wrote:
mikejmoffitt wrote:
The megadrive sync should be properly buffered, no wacky RC stuff should be needed. Just about any CMOS 74' chip will do the job (I have a lot of 74HC04 inverters lying around, so I'll just pass it through two inverter gates as a buffer).

Image


So I tried this circuit with the 74HC04 inverter IC on both my A20F1 and a D14H1 BVM's and I could not get it to work on either of them. I verified that the inverter IC was receiving 5volts from the console. I'm providing sync via the composite video as sync pin from the console. Is this OK or do I need to provide sync from the csync pin?

You will have to use the sync signal. It will not work with composite video.

I just realized my image had the top part drawn in a confusing way; I've fixed it:

Image


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Wed Nov 02, 2016 1:55 am 



Joined: 04 Jun 2015
Posts: 115
mikejmoffitt wrote:
xga wrote:
mikejmoffitt wrote:
The megadrive sync should be properly buffered, no wacky RC stuff should be needed. Just about any CMOS 74' chip will do the job (I have a lot of 74HC04 inverters lying around, so I'll just pass it through two inverter gates as a buffer).

Image


So I tried this circuit with the 74HC04 inverter IC on both my A20F1 and a D14H1 BVM's and I could not get it to work on either of them. I verified that the inverter IC was receiving 5volts from the console. I'm providing sync via the composite video as sync pin from the console. Is this OK or do I need to provide sync from the csync pin?

You will have to use the sync signal. It will not work with composite video.

I just realized my image had the top part drawn in a confusing way; I've fixed it:

Image


Thanks for confirming that I have to use the sync signal, Mike.

I assume that I'll have to include a 220μF cap and 75Ω resistor on this sync signal too?


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Thu Nov 03, 2016 12:20 am 



Joined: 13 Jul 2016
Posts: 48
xga wrote:

I assume that I'll have to include a 220μF cap and 75Ω resistor on this sync signal too?


I believe you do need to include both. Thanks again for helping out xga, As you know Inwas abroad for a few days but I'm glad that progress to fix this is being done! Let me know if I can help testing, I tried wirring the sync from both the csync leg of the chip and from the sync of composite leg, with and without caps and resistors, nothing works.

I can of hope for a more universal solution for the BVM-A20 rather than modifying the consoles one by one.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Fri Nov 04, 2016 2:10 am 


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Joined: 08 Jan 2016
Posts: 275
Location: San Jose, CA
For the sync signal going to the 74HC04 (or other 74' chip) you do not need any caps or resistors; just going straight to the chip's input is best. I've only used monitors which have a high impedance sync input, treating it as a TTL level signal. A monitor with a 75Ω terminated sync input would be better treated with viletim's advice.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Wed Dec 07, 2016 11:29 am 



Joined: 04 Jun 2015
Posts: 115
Just an update on this sync issue with the BVM-A20F1. I tried the suggestions from mikejmoffitt and viletim without success. I did not try the suggestion from Fudoh regarding the programmable oscillator, but I suspect that might be the option that actually works. I say this as I finally got my hands on a Japanese Sega Mega Drive and after connecting it to my BVM-A20F1, it syncs perfectly without issue. All I can think is that the BKM-68X RGB input board is super picky on the frequency of the sync signal.

I'm still unsure on how to fix the issue with my Japansese Neo Geo AES though...


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Wed Dec 07, 2016 1:01 pm 


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Quote:
I'm still unsure on how to fix the issue with my Japansese Neo Geo AES though...

same suggestion: you need a new crystal to bring your AES's output closer to NTSC specs.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Mon Dec 12, 2016 12:15 am 



Joined: 13 Jul 2016
Posts: 48
Fudoh wrote:
Quote:
I'm still unsure on how to fix the issue with my Japansese Neo Geo AES though...

same suggestion: you need a new crystal to bring your AES's output closer to NTSC specs.


Fudoh wouldn't it be possible to come up with a universal sync solution for the BVM-A20F1M so that you don't have to mod the consoles one by one?


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Mon Dec 12, 2016 9:48 pm 



Joined: 18 Apr 2013
Posts: 112
Location: London
xga wrote:
Just an update on this sync issue with the BVM-A20F1. I tried the suggestions from mikejmoffitt and viletim without success. I did not try the suggestion from Fudoh regarding the programmable oscillator, but I suspect that might be the option that actually works. I say this as I finally got my hands on a Japanese Sega Mega Drive and after connecting it to my BVM-A20F1, it syncs perfectly without issue. All I can think is that the BKM-68X RGB input board is super picky on the frequency of the sync signal.

I'm still unsure on how to fix the issue with my Japansese Neo Geo AES though...



What is the serial number of your AES ?
I am big fan of Neo Geo and owns several models and I noticed that some of them have a more compatible signal than others.
While, I dont have issue at the moment with my BVMs, I do remember that when I hd the pvm 2950qm, I could not have a sync with several AES.
The only one compatible was one of the initial euro 60hz that were released in France early 90's.
I notice also that it was the only one which was displaying 240p on the xrgb-mini, all the others are 241p.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Mon Dec 12, 2016 11:30 pm 



Joined: 04 Jun 2015
Posts: 115
amaradona wrote:
xga wrote:
Just an update on this sync issue with the BVM-A20F1. I tried the suggestions from mikejmoffitt and viletim without success. I did not try the suggestion from Fudoh regarding the programmable oscillator, but I suspect that might be the option that actually works. I say this as I finally got my hands on a Japanese Sega Mega Drive and after connecting it to my BVM-A20F1, it syncs perfectly without issue. All I can think is that the BKM-68X RGB input board is super picky on the frequency of the sync signal.

I'm still unsure on how to fix the issue with my Japansese Neo Geo AES though...



What is the serial number of your AES ?
I am big fan of Neo Geo and owns several models and I noticed that some of them have a more compatible signal than others.
While, I dont have issue at the moment with my BVMs, I do remember that when I hd the pvm 2950qm, I could not have a sync with several AES.
The only one compatible was one of the initial euro 60hz that were released in France early 90's.
I notice also that it was the only one which was displaying 240p on the xrgb-mini, all the others are 241p.


Model No. is NEO-0 (3 - 5)

Serial No. is 122206


Last edited by xga on Sat Feb 25, 2017 2:54 am, edited 1 time in total.

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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Dec 13, 2016 2:15 am 



Joined: 16 Oct 2010
Posts: 131
Location: Perth, Australia
I'm expecting a US model Genesis to arrive in the next week or two, will test with my BVM A and report my findings.

Good work on finding that service manual btw. Anyone know if the BVM A20F1U service manual is available somewhere?


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Dec 13, 2016 4:44 am 



Joined: 04 Jun 2015
Posts: 115
BubbaMc wrote:
I'm expecting a US model Genesis to arrive in the next week or two, will test with my BVM A and report my findings.

Good work on finding that service manual btw. Anyone know if the BVM A20F1U service manual is available somewhere?


I have the A20F1U service manual if you want it?


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Dec 27, 2016 1:19 am 



Joined: 04 Jun 2015
Posts: 115
In case anyone is interested, I connected my PAL Mega Drive (modded to NTSC), JPN Mega Drive and JPN Neo Geo AES to my Extron RGB interface and noted the following frequencies:

PAL Mega Drive set to NTSC: H = 15.48KHz - V = 59.3Hz

Image

JPN Mega Drive: H = 15.62KHz - V = 59.9Hz

Image

JPN Neo Geo AES: H = 15.69KHz - V = 59.4Hz

Image

As you can see from the results above, the vertical frequency of the JPN Mega Drive (59.9Hz) is very close to 60Hz (off by 0.16%). The PAL Mega Drive and JPN Neo Geo AES are out by 1.16% and 1% respectively. Unless anyone has any other ideas, I am going to assume that the BKM-68X RGB input board is very sensitive to vertical frequencies and wants a frequency as close as possible to 60Hz to be happy and function correctly.

I imagine the sensitivity of the vertical frequency with the BKM-68X input board might be able to be relaxed and allowed to sync with a greater range by dumping the ROM, disassembling it and modifying values for accepted vertical frequencies. This is only a hunch though.

In the mean time, I think the easiest option is to only use / source genuine NTSC consoles with the A20F1's or get a D20F1 instead and be done with the headaches.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Dec 27, 2016 1:23 am 



Joined: 04 Jun 2015
Posts: 115
Fudoh wrote:
Quote:
I'm still unsure on how to fix the issue with my Japansese Neo Geo AES though...

same suggestion: you need a new crystal to bring your AES's output closer to NTSC specs.


Would a genuine US Neo Geo AES console sync any closer to 60Hz than a JPN Neo Geo AES console? Would they have different crystals? I thought that both would be identical as they're both NTSC units. Would anyone with a US Neo Geo AES be able to test with a Extron RGB interface to confirm, please?


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Tue Dec 27, 2016 12:31 pm 


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Location: America
on some of these BVM's is there something like a "VCR" setting?

I've heard turning that on will sometimes fix sync issues.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Wed Dec 28, 2016 1:30 am 



Joined: 04 Jun 2015
Posts: 115
Blair wrote:
on some of these BVM's is there something like a "VCR" setting?

I've heard turning that on will sometimes fix sync issues.


Unfortunately the "A" series of BVM's don't have the VCR or AFC setting like previous models do. :(


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Sun Feb 19, 2017 12:42 am 


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PeterWar wrote:
Update: My Neo Geo cable from retrogaming cables arrived today, I've been testing it in my Sony Trinitron CRT, perfect picture, no flaws. I've tested it again on my BVM-A20F1M and got image distortion, this time the games are actually playable, but the image is skewed to the right as seen in the picture.

Image



hi

I have a BVM-A20F1M and am experiencing exactly the same image distortion on my jp neo geo aes.
my japanese megadrive works totally ok though - except when it's playing a master system cart in which case I get the same image distortion again (!!)

in both cases the monitor syncs, but the image looks warped like in the quoted image.

I don't think there's much to be done about this issue other than getting another monitor but if anyone on this thread figured out a workaround I'd be grateful for some hints! :wink:


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Mon Feb 27, 2017 1:24 pm 



Joined: 05 Dec 2012
Posts: 335
I was curious about something: Has anyone who's had Genesis / Neo Geo issues with the BKM-68x tried those consoles through the composite video or S-Video inputs? I assume the incompatibilities would be with the 68x itself, but I just wanted to confirm it didn't happen on all input boards of the A-Series.


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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Mon Feb 27, 2017 6:10 pm 


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retrorgb wrote:
I was curious about something: Has anyone who's had Genesis / Neo Geo issues with the BKM-68x tried those consoles through the composite video or S-Video inputs? I assume the incompatibilities would be with the 68x itself, but I just wanted to confirm it didn't happen on all input boards of the A-Series.

I hooked up my SuperGun that operates at 15khz to S-Video and Composite on my A20 BVM and wasn't syncing correctly. My PS2 did fine with 31khz games, though I haven't tested PS1 games on it.
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 Post subject: Re: BVM-A20F1M Sega consoles Sync problems
PostPosted: Mon Feb 27, 2017 6:17 pm 



Joined: 05 Dec 2012
Posts: 335
That's too bad. I have a A-series, but the only thing I tried was SNES via composite and it seemed to work perfectly. I was thinking the best use for the A-series monitors might just be for use with consoles that only output composite or S-Video. When I have time, I'll check again with Genesis over composite and see how it works.


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