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NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: WaldoX on October 05, 2021, 12:40:51 PM

Title: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 05, 2021, 12:40:51 PM
Hello everyone, I am obviously new here, but this seems like the perfect community to try and get some assistance.  I have done a lot of googling already, but have not come across a thread with my exact issue. 

I recently purchased a PC Engine GT from Japan.  When I first received it and tested on batteries, there were no signs of life at all.  Now, I wish I had left it running for a minute to see if any sound started (I have one game to test with), but I didn't.  I flipped the power swtich, saw no signs of life, and turned it back off.  I wish I had played with the volume and brightness wheels, but I can't say that I did.  I know, I did a terrible job of inspecting it's operation, but I expected to have to recap it anyway, so I think that's why I glossed over it.  My bad!  One of the battery terminals had quite a bit of corrosion, so I also ordered an AC Adapter and tried with that once I got it, but same results (and same crappy testing on my part).

Ok, so I did a full recap last weekend, and when I first tested the system after finishing, it appeared to still be dead, which was quite soul crushing, but luckily I left it running, and after 20 or 30 seconds music started playing!  Nice and loud too!  It also seems like the game responded to me pressing start.  Sadly though, the screen doesn't do anything at all.  Not a flicker.  No video, no backlight.

Seems like maybe it's not getting power?  I have a multi-meter, but I'm quite new to all of this and would love a little help in knowing where to test for voltage to the screen, and any other advice you folks may have!

P.S. While most of the old caps had corrosion around their legs, none of them had spilled their contents and damaged anything around them.  I got the old caps off, and cleaned up the pads and all looks good to me.

Thanks again!

Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 07, 2021, 11:26:44 PM
Hello again, I had a chance to do some more testing, and it appears I'm not getting voltage at the red connector for the screen.  I found a thread at badcaps.net that suggested some voltages to check:

Quote
Also, try for the following voltages at these Test points:
TP500 30v
TP501 -24v
TP502 5v (ish, you will see it from 4.8 to 5v depending on factory)

The 2x Variable Resistors adjust the supply rails:
VR500 LCD Voltage Adjust (-24v)
VR501 System 5v Adjust

Here's what I got:

None of those seem off by too much except for VR501, but I don't know enough about any of this to know if that's a problem.  HOWEVER, like I said, I also tried to probe the power connector for the screen directly, and cannot get any sort of voltage reading out of it! 

I also don't get anything from TP901 which is next to the connector, but I also don't know what I should get there. 

Click here for a closeup of the area around the connector. (https://www.badcaps.net/forum/attachment.php?attachmentid=246115&stc=1&d=1633662880)

Notice what might be cap fluid lurking around?  Do you think there could be damage under those grey blobs that is preventing those pins from getting power?

Any advice is appreciated!  Thanks!
Title: Re: PC Engine GT - No Video or Backlight
Post by: Keith Courage on October 08, 2021, 01:33:42 AM
Check the traces+connections for both 4.7UF capacitors and the two 100UF caps near them. Make sure the same voltages are going through the via holes since these are what normally short out from old cap leakage.
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 08, 2021, 06:31:12 PM
Check the traces+connections for both 4.7UF capacitors and the two 100UF caps near them. Make sure the same voltages are going through the via holes since these are what normally short out from old cap leakage.

Hello and thanks for the reply!  I have carefully inspected the areas you mentioned and don't see any broken traces or connections.  I have tested voltages at the capacitors you mentioned, and I tested many many vias in the area.  Here are some pictures showing my results.  I think there's an obvious problem at CC503 with it reading 0 volts?  The vias right next to it are reading well, so I think I had better pull that cap and see what it going on under there.  Any other advice?



Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 08, 2021, 06:33:12 PM
And here are the other 2 pics:

Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 08, 2021, 07:15:20 PM
I may have found the problem!!!! I haven't had a chance to remove that cap yet, but I realized I had taken some pictures during the recap, so I went back and found a picture of the pads for CC503. There is CLEARY corrosion on the bottom 1/3, and that seems to be exactly where it connects to the trace. I've very new to all of this, and probably thought since 2/3 of the pad looked good, all would be well. Lesson learned!

(https://www.badcaps.net/forum/attachment.php?attachmentid=246184&d=1633734735)

The pads looks scratched up from me trying to remove some of the corrosion with my tweazers and some deoxit. I suspect if I can't remove more of that corrosion I'll need to either scrape away some of the solder mask at the edge of the trace and connect to that? Or can I run a jumper over to the via? Thoughts?

Thanks!
Title: Re: PC Engine GT - No Video or Backlight
Post by: MasterofBiscuits on October 09, 2021, 02:37:10 PM
That should easy enough to sort, on the + side you can run a connection to the via that the pad runs to, and on the - side there is a big fat pad you can scrape back. I had a missing + pad on this cap on a previous machine and I found it neater to use a leaded electrolytic cap so I could put the wire into the via hole.

I'm fairly sure this cap is part of the backlight circuit so I think this may well be your problem.
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 09, 2021, 08:07:22 PM
 ](*,)  Ugh, I knew I shouldn't have been celebrating so soon, but damnit it felt good.  Turn out, it was just my ignorance leading me to incorrect assumptions.

I was looking for -24V on that cap, but I don't really know what "negative voltage" is, so I didn't realize I needed to check for the voltage on the negative side of the cap.  It was there all along.  In fact, when I removed the cap, I found fairly pristine pads underneath; turns out I took that picture before I went back and cleaned up the pads.  Here's what they actually look like:

(https://www.badcaps.net/forum/attachment.php?attachmentid=246251&stc=1&d=1633824153)

I've looked at this board up and down a magnifying glass and I still have no idea why there's no power here:

(https://www.badcaps.net/forum/attachment.php?attachmentid=246252&stc=1&d=1633824153)

Do you think I need to scrape away the grey goo, and is that safe?

Thanks

:(
Title: Re: PC Engine GT - No Video or Backlight
Post by: MasterofBiscuits on October 12, 2021, 12:40:50 PM
That sucks.

I have a freshly recapped machine here that is fully working so I checked the voltages you have above. Most are the same, but a few are different.

- Positive side of CC503 (22uf cap) should show 24.2v
- The vias that you note are fluctuating should show 7.3v

I would test the transistors around the red backlight connector and also check and double-check the traces and vias in that area as I think your problem lies there.

The good news is if it's just the backlight, you can work around this by replacing the LCD with a modern one.
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 12, 2021, 04:11:41 PM
That sucks.

I have a freshly recapped machine here that is fully working so I checked the voltages you have above. Most are the same, but a few are different.

- Positive side of CC503 (22uf cap) should show 24.2v
- The vias that you note are fluctuating should show 7.3v

I would test the transistors around the red backlight connector and also check and double-check the traces and vias in that area as I think your problem lies there.

The good news is if it's just the backlight, you can work around this by replacing the LCD with a modern one.

Wow, thank you so much for doing that!  I have actually been contemplating doing the LCD mod as a work-around to my issue, but just want to confirm if I can, that my issue is just the backlight and not the video signal.  Do you know of any way to check that?
Title: Re: PC Engine GT - No Video or Backlight
Post by: MasterofBiscuits on October 13, 2021, 06:42:24 AM
Since you confirmed no voltage on the backlight power connector I think it's safe to say it's just the backlight (it would be pretty unusual for the video to go too) - you could try shining a torch at the LCD while it's connected to see if you can make out any pixels but this is kinda tough to see in my experience.
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 13, 2021, 09:30:46 AM
Since you confirmed no voltage on the backlight power connector I think it's safe to say it's just the backlight (it would be pretty unusual for the video to go too) - you could try shining a torch at the LCD while it's connected to see if you can make out any pixels but this is kinda tough to see in my experience.

Hello and thanks for the reply.  I thought I had confirmed no power, but turns out I'm just an ignorant monkey poking at things I don't understand.  Here's what someone at badcaps.net had to say:

Quote
... but just FYI, that red connector is probably for supplying power to the CCFL backlights of the LCD. IDK what voltage and current those would require with this being a handheld device, but even small CCFLs in 13-15" LCD monitors still run at 500-700V AC. So I expect the small CCFLs in this screen to still be running at relatively high voltage and probably a few mA of current or less (with total power possibly under or around a Watt.)

For this reason, don't expect to be able to measure any voltage on the red connector - not with a regular multimeter anyways. The voltage will likely be high voltage and high frequency AC. It can even damage some cheap multimeters.

Now, I don't know if they're correct, but it's much more likely that they are than me.  :-(
Title: Re: PC Engine GT - No Video or Backlight
Post by: MasterofBiscuits on October 13, 2021, 11:54:33 AM
That is true, CCFLs use high voltage circuits - however, the voltage on the positive terminal on that red connector should show a nominal voltage when running (4-6v - I just tested it). So you can check that. I assume the voltage is stepped up within the LCD unit itself (if you open it up, you'll see a circuit board with a high voltage warning on it).

Edit: Does the screen look like this when you turn it on? https://i.imgur.com/zeY7VFn.jpg
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 13, 2021, 04:02:40 PM
That is true, CCFLs use high voltage circuits - however, the voltage on the positive terminal on that red connector should show a nominal voltage when running (4-6v - I just tested it). So you can check that. I assume the voltage is stepped up within the LCD unit itself (if you open it up, you'll see a circuit board with a high voltage warning on it).

Edit: Does the screen look like this when you turn it on?

Thank you for checking the voltage on the red connector, that gives me something to go on.  My screen doesn't come on AT ALL.  No flicker, nothing.  After I recapped it, I thought the entire unit was completely dead, but luckily I pressed Run and heard the game music start!
Title: Re: PC Engine GT - No Video or Backlight
Post by: MasterofBiscuits on October 14, 2021, 08:25:33 AM
You may have a video problem as well then - the above unit is what a dead backlight looks like, the LCD has it's own 'glow' which will change if you play with the brightness wheel - or maybe the LCD unit itself has failed.
Title: Re: PC Engine GT - No Video or Backlight
Post by: Keith Courage on October 14, 2021, 10:01:51 PM
If you can't find the problem, the system would still be a good candidate for a 3.5" LCD screen upgrade since the replacement screens have their own back lights.
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on October 15, 2021, 12:26:30 PM
If you can't find the problem, the system would still be a good candidate for a 3.5" LCD screen upgrade since the replacement screens have their own back lights.

That was my take as well, and my 3.5 screen kit is on the way.  :-)
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on November 24, 2021, 05:44:05 PM
Just wanted to update and say that my cheap chinese soldering iron has started falling apart, so I'm waiting for a new one before I attempt this screen mod.   :|

I will update this thread though once I get around to the mod.  I won't lie, this mod scares me quite a bit, it'll be some of the smallest work I've done yet.  Wish me luck!   :bonkthis:
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on December 24, 2021, 07:15:56 PM
Okay Gents (and ladies?), I finally got to this screen mod and....... wait for it.....STILL DOESN'T WORK!!!   ](*,) ](*,) ](*,)   

Essentially it's the same as before: I can hear the game playing, but I get no video.  The screen does light up (new backlit lcd), but no picture of any kind, just a blue background.  If I haven't made any mistakes, then what does this mean?  Does it mean the 6260 is dead or malfunctioning?  Any advice to troubleshoot further is really appreciated.

I modded my LCD Board for 5V according to this video: Turbo Express LCD Screen Mod! Installation guide and demonstration (https://www.youtube.com/watch?v=0cGiftQSqBw&t=732s).  I followed this video in general, but was using a different video board, so I followed Console5's instructions on connecting it up.

I tested everything for continuity, and checked for bridges.  I tested for 5V at the capacitor and the video board.  I tested the 5V connection on the back for the LCD.

P.S. I don't know what the potetiometer on the video board is for, but I did try turning it completely both ways while powered up.

Incoming Picture Tsunami!!! 

Pins to lift marked(https://i.postimg.cc/hvXYyzzF/pings-marked.jpg) (https://i.postimg.cc/x8dQ01Xg/pings-marked.jpg)Lifted and Connected (I noticed the wonky cap at this point; I had apparently "repaired" it in the past and the connection was loose.  I replaced it with another later on)(https://i.postimg.cc/xTb7LmVM/lifted.jpg) (https://i.postimg.cc/KYrhBMLJ/lifted.jpg)

Grounded(https://i.postimg.cc/x8B4WfMX/lifted-and-grounded.jpg) (https://i.postimg.cc/m2t4Jhfg/lifted-and-grounded.jpg)Grounded Alt View(https://i.postimg.cc/4dLMQb3b/lifted-and-grounded-2.jpg) (https://i.postimg.cc/9XxVLZkk/lifted-and-grounded-2.jpg)
Done. Overhead(https://i.postimg.cc/FRs8SnhH/all-done-big.jpg) (https://i.postimg.cc/4dPZk9xm/all-done-big.jpg)Video Board(https://i.postimg.cc/8zR00V5C/all-done-close.jpg) (https://i.postimg.cc/gkQpWdmq/all-done-close.jpg)

LCD Board w 5V mod(https://i.postimg.cc/YStscyGz/lcd-board.jpg) (https://i.postimg.cc/NjXcGV0h/lcd-board.jpg)Pin 20 Connection(https://i.postimg.cc/cLyzhJdj/zoomed-20.jpg) (https://i.postimg.cc/wBdd1Vt1/zoomed-20.jpg)
Pin 26 and Nearby Cap Connections(https://i.postimg.cc/jq1mWXmR/zoomed-26-and-cap.jpg) (https://i.postimg.cc/76H8VZnD/zoomed-26-and-cap.jpg)


Pin 26, 33 and 40 Connections(https://i.postimg.cc/W3HWkN95/zoomed-40-33-26.jpg) (https://i.postimg.cc/wvwKbYwN/zoomed-40-33-26.jpg)Pin 33 and 40 Connections(https://i.postimg.cc/C11r5B4Z/zoomed-40-and-33.jpg) (https://i.postimg.cc/7hRFwM8Y/zoomed-40-and-33.jpg)Mod Board Pin Connections(https://i.postimg.cc/yWqLLfC9/zoomed-board-pin-connects.jpg) (https://i.postimg.cc/wjLCYmWg/zoomed-board-pin-connects.jpg)
Mod Board 5V and Cap(https://i.postimg.cc/2jPmprzd/zoomed-board-5-V-and-cap.jpg) (https://i.postimg.cc/ZYDt8ZBt/zoomed-board-5-V-and-cap.jpg)Mod Board Resistors
(https://i.postimg.cc/d3ZWRbpw/zoomed-board-resistors.jpg) (https://i.postimg.cc/J00ffYF2/zoomed-board-resistors.jpg)
LCD Board Pin 1 5V Connection(https://i.postimg.cc/3w9b3C25/zoomed-lcd-board-pin1.jpg) (https://i.postimg.cc/7YGvXc0C/zoomed-lcd-board-pin1.jpg)LCD Board VR 5V Connection(https://i.postimg.cc/sfBy0vRD/zoomed-lcd-board-power-reg.jpg) (https://i.postimg.cc/gkfC7DHg/zoomed-lcd-board-power-reg.jpg)

LCD Power and Ground Connections
(https://i.postimg.cc/DZn64WdQ/lcd-power-and-ground.jpg) (https://i.postimg.cc/SK0Dq1nv/lcd-power-and-ground.jpg)

Title: Re: PC Engine GT - No Video or Backlight
Post by: Keith Courage on December 26, 2021, 12:50:19 AM
Your Video board has the traces going to different places than what I'm used to doing. This is the circuit I use minus the extra 75ohm resistor on the output. (https://i.postimg.cc/NFPnWfHJ/pce-Composite-Video-repair.gif)

As you can see, all 4 signal pins should be connected together after passing through their resistors. On your board they are not doing that. Also, 3 of your signal pins(20,26,33) are going to a spot with no transistor installed.

I also have no idea why there is a Potentiometer on there nor do I see why there is an extra Ceramic cap on your video board.

Here is one built from scratch. 
(https://i.postimg.cc/kX94KcSJ/106101844-2576375702626036-2677354549841987394-n-1.jpg)

Also, here is a wiring guide for the LCD. https://mega.nz/file/IMw2hLLL#v667H2EfnD1HEcMF45zp-sSw311BdsKM-JAZJJPRUtI
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on December 27, 2021, 10:52:12 AM
Hey, thanks so much for the reply! 

As you can see, all 4 signal pins should be connected together after passing through their resistors. On your board they are not doing that. Also, 3 of your signal pins(20,26,33) are going to a spot with no transistor installed.

I completely agree that this seems BONKERS.  I'm having a hard time believing that Console5 would be selling a faulty board, but this is so weird!  Here are their pictures for this board:

EDIT: I was taking another look at Console5's board, and it appears to me that all the resistors do connect together and run through the single transistor on the board.  It looks to me like the PCB has multiple paths running around, but only utilizes one of them.  I'm a total noob at this though...

(https://i.postimg.cc/Z5hstT3W/pcegt-pcb.jpg) (https://i.postimg.cc/JzWXPSLc/pcegt-pcb.jpg)(https://i.postimg.cc/qMKD5ttf/pcegt-composite-pcb-connections.jpg) (https://i.postimg.cc/X75FK4TY/pcegt-composite-pcb-connections.jpg)

I should be getting some variety packs of resistors in soon and can try building one like yours, or I also have these boards that I can try once I get those resistors in.

(https://i.postimg.cc/kgc0TVZJ/AV-Board-w-vid-out.png) (https://i.postimg.cc/kgc0TVZJ/AV-Board-w-vid-out.png)



 :boom: Would you mind though, just for a moment, assuming that their board works?  If it works, and I didn't screw it up, what would this mean for the PCE GT?  Bad video chip?


Thanks again!

Title: Re: PC Engine GT - No Video or Backlight
Post by: Keith Courage on December 27, 2021, 09:37:22 PM
I've never seen a HU6260 chip produce absolute no video at all. If bad, the colors or graphics are generally just all messed up.

I'm not saying it couldn't happen where the chip is dead altogether and won't produce any picture whatsoever. I've just never come across one that has done that.



Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on December 27, 2021, 09:50:43 PM
I've never seen a HU6260 chip produce absolute no video at all. If bad, the colors or graphics are generally just all messed up.

I'm not saying it couldn't happen where the chip is dead altogether and won't produce any picture whatsoever. I've just never come across one that has done that.

Well that good to hear, I'll keep my fingers crossed that there's still hope here.  I noticed your version of the video board doesn't use a transistor, any idea what the other boards need one for?  Just curious!  I'll try making a board like yours or using one of these others I have and get back to you.

Thanks again!
Title: Re: PC Engine GT - No Video or Backlight
Post by: Keith Courage on December 28, 2021, 02:39:13 AM
The 75ohm resistor is just to lower the Brightness slightly but I think that's mainly just needed for other transistors that amp the signal more. I've noticed that the 8050 transistor has the correct brightness without one and will be too dark with one.
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on December 29, 2021, 10:03:30 AM
The 75ohm resistor is just to lower the Brightness slightly but I think that's mainly just needed for other transistors that amp the signal more. I've noticed that the 8050 transistor has the correct brightness without one and will be too dark with one.

Thanks for that extra advice!  I just ordered a handful of those transistors, along with some prototyping board.  In a couple of weeks when that comes in, hopefully my resistor bible will be here too, and I'll get back to work on this project.

Thanks again!  Happy New Year!   :)
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on January 20, 2022, 01:06:30 PM
I have gotten all of the parts in for the AV boards, so I'm hoping to tackle this project again this weekend.  I have 2 options for my Composite AV Board, I can build one with your (Keith's) schematic on prototyping board, and/or I can populate one of the boards I ordered from OshPark.

The boards from OshPark include an additional AV hookup on the board for doing an AV Out mod.  Does anyone know of any guides on doing AV Out?  I'd love to know how to repurpose the com port for this, if that's possible?  I've tried searching these forums and the internet in general, but haven't been able to find any guides on this.   :'(
Title: Re: PC Engine GT - No Video or Backlight
Post by: MasterofBiscuits on January 24, 2022, 06:30:30 AM
I have gotten all of the parts in for the AV boards, so I'm hoping to tackle this project again this weekend.  I have 2 options for my Composite AV Board, I can build one with your (Keith's) schematic on prototyping board, and/or I can populate one of the boards I ordered from OshPark.

The boards from OshPark include an additional AV hookup on the board for doing an AV Out mod.  Does anyone know of any guides on doing AV Out?  I'd love to know how to repurpose the com port for this, if that's possible?  I've tried searching these forums and the internet in general, but haven't been able to find any guides on this.   :'(

I don't have a guide, but I have seen people add a composite contact to the headphone jack. It involves drilling a tiny hole through it and inserting a wire. Repurposing the com port might be easier since you could just add in a 4 conductor jack, or any other type of port you wanted. Since there's no definitive standard for 3.5mm av cables, I'd recommend buying the cable first then wiring your socket to match it.
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on January 24, 2022, 11:17:36 AM
Thanks for the advice, it's much appreciated!

FWIW, I built the Osh Park board this weekend, then before installing it I was going over the PCEGT board looking for problems and doing basics like checking voltages, and I blew a fuse somehow  :-/   I had to order fuses, so the project is on hold again.   :roll:

Title: Re: PC Engine GT - No Video or Backlight
Post by: Keith Courage on January 24, 2022, 05:23:04 PM
I just re-purpose the comport Jack for video out and then just use the headphone jack for the audio instead of installing a new port. 
Title: Re: PC Engine GT - No Video or Backlight
Post by: WaldoX on January 25, 2022, 09:39:03 AM
That sounds like what I was looking for, and I think I can figure out the rest on my own, but honestly, if I can just get this thing working, I'd be so happy.