Hitachi 27" 27MM20B Dual-Scan CRT TV??

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kitty666cats
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by kitty666cats »

Looking forward to seeing someone get a RGB mod goin’ on one of these! As the owner of a Sampo/NetTV SME-23DL3(P) - which is a SME-32DL5 sans 15kHz YPbPr - I must say CRTs like these are a blessing and make you hyped just seeing them sittin’ there, lol
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loopyeddie
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by loopyeddie »

All three that I receive will be RGB modded as soon as possible.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

First unit was received and theres a problem. Vertical collapse. This was the unit that produced all the images Ive posted in this thread, it was working perfectly fine prior to shipping out. I've advised him to open the unit and re-seat all connections first, then prod around with a plastic rod or ruler to see if its something like a cracked solder joint, if he can locate the general area.

Any ideas on what to check anyone?

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maxtherabbit
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

fingers crossed the vertical deflection coil just got unplugged
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Hoagtech
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Hoagtech »

What connection is he using and with what console. I’m sure it’s a simple setup error..
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bobrocks95
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by bobrocks95 »

Hoping it was a buyer savvy enough for you to be able to, say, link them here and show you're doing everything you can. Just thinking about how much ebay complaints suck for sellers and all that.

Best of luck with these! I'd have definitely gotten one in my CRT hunting days.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Hoagtech wrote:What connection is he using and with what console. I’m sure it’s a simple setup error..
Unfortunately its not. I have been having some issues with sets working 100% fine leaving here but not powering on or giving issues upon arriving at destination. This has happened to two out of 8 sets shipped thus far, and 4 of the 8 shipped have yet to be tested. Im 99% sure its due to cracked solder joints as I examined a DOA set that came right off the initial truckload that would powerup and get screen voltage, sound, etc but no picture at all and I found a medium sized 3 legged transistor that was basically floating on the mainboard. All 3 solder joints had cracked. I pulled the mainboard, which is not trivial because its very large and has a lot of connections, a couple of which must be unsoldered or cut (to the neckboard). I have repaired those joints and am in the process of examining the board for additional issues / weak looking joints and will attempt to put the board back in and see if I can bring the set back to life. Based on what Ive seen on this board, I believe its very likely that any set I ship that has an issue upon delivery is due to a cracked solder joint(s) on the mainboard. Anyone that is competent in soldering and has the know how to disconnect and pull the mainboard has a really good chance at finding and fixing the issue if they closely examine the underside (solder side) of the mainboard with a magnifying glass (helps) and then reflowing with some additional new solder and flux.

What Im saying is that the only guarantee I can give when selling these sets is that they work fine up until leaving my location. External physical shipping damage will be covered by insurance, but not something like cracked solder joints from jostling during transit. I try to pack these things competently to avoid physical damage. So if you do want to buy, be advised that I can offer no warranty and it is at your own risk. I truly believe that most of these issues can be easily fixed by locating and reflowing the problem solder joints, which are most likely on the bottom of the mainboard-- but the mainboard is large and its not a trivial task to pull it, at least for me.

Please keep all this in mind if you order these. I will help in any way I can, but these are going to have to be "buy at your own risk". I recommend buying 2 or 3 at a time to better your chances of getting a working set, and then proceeding to check any set that arrives with issues in your own good time.

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Last edited by Josh128 on Fri Sep 03, 2021 3:02 pm, edited 1 time in total.
fernan1234
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by fernan1234 »

Dang that's a bummer, and a bit surprising since they're paletted and terminal-to-terminal, but they are huge beasts and not pro-grade so likely not as resistant to shock and vibration as we would wish.

What shipping company are you using? It may be worth changing to a different one to see what difference it may make. Clearly the current one is not being too gentle with them.
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maxtherabbit
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

if the problem is poor solder joints as he suspects, the type of shipping wouldn't matter much - the thermal cycling of moving them inside/outside is likely enough to crack such poor soldering
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

fernan1234 wrote:Dang that's a bummer, and a bit surprising since they're paletted and terminal-to-terminal, but they are huge beasts and not pro-grade so likely not as resistant to shock and vibration as we would wish.

What shipping company are you using? It may be worth changing to a different one to see what difference it may make. Clearly the current one is not being too gentle with them.
I use a freight broker, who obtains quotes from different carriers. So far Ive shipped with Old Dominion (who has a very good reputation), AAA Cooper, R&L Carriers, FedEx Freight, and the independent driver who brought me the initial shipment. Out of the initial shipment, of which Ive tested maybe half, I had 2 sets that would get HV to the tube and had audio, and you could hear the inputs changing, but they had no screen. One of those is with the board above. So its not the carriers. Both of the buyers reported that the packages looked good, just like the photos I sent them from the dropoff terminal. So I think its just the age, size, and weight of the mainboard, for the most part. Im curious as to whether this fix above will get this unit working, and what I find in the second unit with the identical issue.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

maxtherabbit wrote:if the problem is poor solder joints as he suspects, the type of shipping wouldn't matter much - the thermal cycling of moving them inside/outside is likely enough to crack such poor soldering
Thats another good point. The inside of a box truck in the heat of the summer likely can reach in excess of @125F, so there is definitely thermal cycling going on. We'll see how it goes. I may have to adjust pricing and /or ship under the strict understanding that these 100% work going out the door, but no guarantees as to what happens after transit.
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by fernan1234 »

Josh128 wrote:I may have to adjust pricing and /or ship under the strict understanding that these 100% work going out the door, but no guarantees as to what happens after transit.
You probably already know this, but for the ones you sell on eBay even if you write this in the description you'll be 100% SOL if a buyer initiates a return request due to it being DOA. I guess your best chance would be to send a direct message to buyer asking them to explicitly agree to these terms before you ship.

And if we're suspecting thermal cycling, it may also be better to hold off until temperatures drop before continuing to ship these.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Im going to work with the first few buyers that have issues, and I definitely feel for them, but going forward I want everyone interested in buying to know that this is strictly the only conditions under which I will sell them. Otherwise I would just sell them locally only, because its an incredible amount of work to pack and ship these things. You know the drill. This is old tech, and tubes of ANY kind this size or larger are notoriously prone to experience issues in shipping. Its either take a chance on these or spend $1000+ on a 20" PVM, which most likely will still require you cover the shipping cost to return the item for the refund.

Logic dictates that other than extreme issues like shadow mask detachment, which I have notoriously experienced with a brand new Wei-Ya unit (and though the seller did refund me the cost of the unit, I was still out $330 for shipping) that issues like the OP set of this thread having a beautiful, pristine picture upon last power down and shipping, then having vertical collapse after shipping and powering back on, are overwhelmingly most likely caused by a loose connection or cracked solder joint as seen above. Its very unlikely that an IC, or cap, or other component would just fail with no power applied. Im confident these types of issues can be found and fixed by a competent DIYer or electronics guy.
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bobrocks95
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by bobrocks95 »

Going off of what fernan said, might want to pull the ebay listing for now until you get a better idea of how to handle the problem.
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matt
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by matt »

Josh128 wrote:First unit was received and theres a problem. Vertical collapse. This was the unit that produced all the images Ive posted in this thread, it was working perfectly fine prior to shipping out. I've advised him to open the unit and re-seat all connections first, then prod around with a plastic rod or ruler to see if its something like a cracked solder joint, if he can locate the general area.

Any ideas on what to check anyone?
Vertical collapse is usually not hard to fix, since the vertical section tends to be fairly small and easy to spot. The schematic is on page 116 of the service manual. Total collapse is most often caused by a failed vertical deflection IC, which in this IV is label I601. If it is indeed a bad solder joint, it will probably be on this chip or the connector to the vertical coil on the yoke. The chip is still available and fairly cheap if a replacement is needed:

https://www.arcadepartsandrepair.com/st ... ps/an5521/

Hopefully this is due to a bad solder joint (which seems likely). If the IC itself is bad, the failure often is caused by a bad capacitor, so changing the caps in this area should be done to avoid the problem coming back. The usual culprit is the pump-up capacitor (C506, 100uF/35v).
Josh128 wrote:I pulled the mainboard, which is not trivial because its very large and has a lot of connections, a couple of which must be unsoldered or cut (to the neckboard).
I typically just remove the neck board from the tube and leave it attached to the chassis if I have to pull the whole unit.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Good news! Just as I had hoped, fixing that transistor solder joint fixed my no picture unit! While inside, I reflowed a few other joints (maybe 6 or so) that looked a bit suspicious. This gives me more confidence that the other units can be repaired. I have another unit opened up just to look around, and the same transistor that was floating on this one feels VERY delicate.

I was also able to take yoke readings requested by Mike Moffitt, Ive also included them.

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maxtherabbit
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

Maybe you should preemptively reflow that transistor on all of them prior to sale?
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Its something Im considering. I have a second unit with the EXACT same symptoms as the one I just repaired. If I see similar issues in that one, I'll definitely have to do that. More work...I did this to myself though-- this was actually my birthday present. Im a glutton for punishment. :(
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nem
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by nem »

Why on earth did you cut the flyback wires? You can just pull off the neck board.
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maxtherabbit
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

nem wrote:Why on earth did you cut the flyback wires? You can just pull off the neck board.
this
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Easy answer- this is much easier, quicker, and less wires and shit in the way when handling the mainboard and flipping it over to examine the solder joints. The neck board is silicone glued on the tube. I'd rather cut these wires than unglue it. Also, theres absolutely nothing wrong electrically in doing this, and theres less of a chance something on the neck board will pop off or get bent or damaged if it stays on the neck vs jostling around loose, hanging by two wires on the mainboard.
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maxtherabbit
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

I'd rather take my chances with an unglued CRT socket than use a gross wire nut but different strokes I guess
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Hoagtech »

maxtherabbit wrote:I'd rather take my chances with an unglued CRT socket than use a gross wire nut but different strokes I guess
Hey now. Come on guys. He obviously was testing his repair with the wire nut in place. Only a fool would solder and heatshrink before a successful test.

I personally would have left the neckboard attached and place a sock over it but the point is he got a dead monitor working..
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Hoagtech wrote:
maxtherabbit wrote:I'd rather take my chances with an unglued CRT socket than use a gross wire nut but different strokes I guess
Hey now. Come on guys. He obviously was testing his repair with the wire nut in place. Only a fool would solder and heatshrink before a successful test.

I personally would have left the neckboard attached and place a sock over it but the point is he got a dead monitor working..
^^

lol right on. I have some more info-- I have a second set here exhibiting the same problem, and guess what, exact same transistor wobbling loose the exact same way. Apparently this is a systemic issue, I think its related to the rear of the mainboard (near the heavy flyback) flexing over time and transit, and this transistor just pops right up. Fixing it up, checking more joints, and looking at doing a crude RGB mod to see if I can get that working.

Heard back from the first buyer, who is troubleshooting his unit, and he found an identically loose transistor, but his was a different one, Q707, while the one I've found on two sets was Q72H. Im having him resolder that one on his set for good measure. Again, his set was the OP set I showed in this thread, working fine up until I shipped it out. Still waiting for word from him to see if resoldering was able to fix it. Very strange how this is occurring, but I'll take it, because so far it appears to be something very fixable with basic soldering skills.
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by yatzr »

I'm the guy that went in on 3 of these with loopyeddie. One of ours was having a similar symptom with no video. I've been messing with it a bit today to try and figure it out.
When you had no video, did you also have no audio? I have no video and no audio, but I do get neck glow, the high pitch whine, and I can hear the "click" when switching between any of the tv input modes and the pc mode. I expect to hear the static noise on the rf tv mode, but get nothing. And I tried giving it audio in pc mode, but all I get is a slight buzz which does actually change slightly when I hit the volume buttons.

I tried looking for any bad solder joints. I didn't see anything obvious like your transistor, but I did reflow everything that looked iffy, including that particular transistor. I also swapped those two big daughter boards into another working monitor, and the daughter boards work fine. I also reflowed all the solder for the connectors on both sides for those daughter boards.

I think it's gotta be something with the circuit that does all the switching of inputs, so I'll start scoping the schematic, but if anyone already knows where I should be looking, that'd be great.


Also, heads up for anyone diving into one of these that there's a cap on the neckboard that holds its charge real well after shutting down. I started manually discharging it after about zapping myself :lol:
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

The first buyer was able to repair his vertical collapse, the OP set is back in business! He messaged me last night, he found broken joints on Q707, which was floating, and an inductor coil I believe. Q707 is a vertical standing transistor that looks just like the transistors I have found loose to make my repairs.

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yatzr - Yes the two units that I was able to repair did have audio / static when on the RF input. Let me ask you this, when you power on, does the tube get high voltage (ie can you feel the static charges about 1 inch away from the front of the tube)? On both my units with the same loose transistor, I did in fact get high voltage to the tube, but no picture at all.


On the first unit I opened up just to take pictures, when I pulled the largest daughterboard (which contains the jungle chip), after putting it back in, the set wouldnt even power up, ie no high voltage to the tube. Turned out that the jungle chip daughterboard was not perfectly seated. Its got 3 connectors on it and you really need to give it some good pressure and wiggle to get it seated well.

The smaller board, right next to the jungle board, is the audio board. The RGB signals from the VGA port are actually routed to this board first, where the signals are filtered before going elsewhere. So the audio board or underside of it can be involved also.

I told Eddie to tell you to focus on the rear underside of the board-- it seems most of the loose / broken joint issues are occuring from either the rear to maybe 5-6 inches toward the center. Whether or not you get screen voltage can help direct you where to look. If no screen voltage, start with the power supply section. There are two glass fuses that Ive seen on the board, make sure those are both good (but I expect they are). Also, when you reflow components like these transistors, its always a good idea to check continuity between the solder joints to make sure none of them are touching - sometimes its hard to see, but it can happen.

Going forward, lets communicate on this issue via email for troubleshooting, and when we find the issue, we'll come back here and post the findings. Ive DM'ed you my email address.
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by loopyeddie »

AMAZING SELLER REVIEW!

yatzr and I purchased 3 monitors on a pallet from Josh128. I direct messaged him and Josh was quick to respond and has very clear communication powers. He sent me invoices for the monitor cost and for the shipper. Josh send pictures of all 3 units running and has numbered them to keep organized. There was no surprises. They shipped from Louisiana to Omaha, NE in about a week. It was really fast. When it arrived here, all I had to do was show up with a pickup truck and they loaded the pallet in with a forklift and I was off!

Once home, I pulled all the packing materials off. Josh did a great job positioning the monitors and squeezing them on the pallet. They actually aren’t super heavy so one person can carry them. I plugged in each monitor one at a time and found that 2 of the monitors were perfect. The 3rd one wouldn’t turn on, but yatzr took it home and reflowed some joints and now it is up and working too. Great work, yatzr!

The picture and geometry in these is great. I am far from an expert, but I do own and use several PVMs and other high quality CRTs. I haven’t been able to test them super thoroughly but it is obvious that these are high quality. I would imagine 99% of gamers would be very content with the picture from these. The actual monitor is good looking too. It has a generic 90’s grey look but is clean and simple. No dumb flourishes or unnecessary functions. These do 15khz and 31khz beautifully and that’s it! Minimal ports and really just 2 inputs. So simple. And the geometry settings is nuts easy to understand and adjust. The sound from these is more than adequate as well. Sure, if you end up with a semi-permanent setup you may want to feed to a more robust audio amp and speakers, but you could do a lot worse than the stock speakers. Way better than pvm sound.

I do believe that these are perfect monitors for retro gaming. All the features you’d want and no fluff. I’m very excited to get an rgb mod onto these then they truly are perfect. I am confident that a very clean and simply to implement mod will be sorted out quickly.

If you are thinking about picking one (or more) of these, do it. We are grabbing 3 more units we are so happy with them. The value in these is astounding and Josh couldn’t be better. What a great experience this has been from beginning to end. Thank You!
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by yatzr »

I did get our one non-working unit back to working. Here's a summary:

Had no video or audio on any inputs. Did have high voltage and neck glow. I assumed it was something with IF/MTS daughterboard (the biggest daughterboard) because that's where the input switching magic happens. However, I put this daughterboard into another working monitor and it was fine. So then I thought maybe the daughterboard isn't getting powered properly. I checked H-VCC pin 16 of PIF1A and it was fine. Then I checked 9V pin 11 of PIF2A and it was not. It was only 150mv. I traced that line back to I believe the source at Q705. The solder joints at Q705 looked fine, but I reflowed them anyway. I also reflowed Q707 which is right next to it (they also looked fine). I plugged everything back in and it just worked. So I assume it was the joints of one of those two transistors.

Once I put the whole tv back together, it wasn't working again. I didn't have high voltage. The only thing I did between when it was working and now was remove my test wires and reattach the metal shield on the underside of the main board. I had removed it and the metal shield from the neck board while I was triaging. I can't imagine that had anything to do with it, but I took it all out again, took that shield back off, put it all back together, and now it's fine. I think it's likely just the act of taking it all out and putting it back together just fixed some connection. And I had definitely triple checked all my connections that first time.

Anyway, this unit is working now and looks great! Thanks Josh!!
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Awesome, glad to hear y'all got it guys!!
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

I am pleased to report I repaired the second no screen unit here. Same Q72H transistor w/ heatsink floating in socket. Fixed it and set fired right up.

To recap repairs for no pic or vert collapse after shipping for all problem units thus far:
Q72H, Q707, and L702 have been confirmed as prone to breaking joints during shipping, Q705 is also suspect. Resoldering and/or reflowing these components has fixed every no-picture issue so far.

Made a first attempt at a 15kHz mod and was partially successful. Using the 240p suite, I can see the image just barely on a blank screen, but when I pull up the OSD, the 240p suite imagery appears perfectly in the geometry of the OSD. Similar to something I saw in one of MikeJMoffits early RGB mod attempts. I navigated to the suites section that allows you to display full screen R,G,B,W and blank/black, I can confirm my color lines seem to be working. I did measure my 5V on the blanking line output of the Genesis when not connected, but when I connect it drops to 1.34V. Suspecting that my blanking resistor setup is not right and perhaps the Genesis is not blanking the screen properly. I was not able to remove the original OSD Blanking grounding resistor (R01R, 2.7K), because I could not find it. Tracing back from the OSD blanking pin on the I001 IC, it doesnt seem to match what the chip schematic shows. Looks like it goes to ground through a diode, which is not shown at all on the schematic. I did go ahead and use a 2.7K on the blanking line from the Genesis, so maybe being that I didnt remove anything, the voltage is being pulled down more than if used a smaller or no inline 2.7k or grounding 75ohm resistor. Can anyone chime in on what else would cause this?

Below is a cool video of me switching colors in the 240p suite while having the menu displayed.

https://www.youtube.com/watch?v=1zpBiNfcMPo

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