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NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: MasterofBiscuits on April 25, 2020, 03:01:46 PM
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I spent the day recapping my PC Engine GT and on reassembling I powered on - backlight comes on but no picture or sound. I checked the board again and I realised I hadn't put a cap on CC502. I put it on but no change.
During the recapping I removed Q500 by mistake while using hot air on the area and it fell off. I put it back on without issue and it seems to be ok (showing continuity and voltage which switches to the other poles when powered, which I think it's supposed to do). I've checked the connections for the caps and they all seem to be ok. I'm not certain on the best way of testing them though.
Does anyone have any suggestions as to what the issue may be, other than I am an idiot that has killed his PCE?
Pics
https://i.imgur.com/L73xfKI.jpg
https://i.imgur.com/zeY7VFn.jpg
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Start checking if all the traces for the caps are good. Especially the two 4.7UF caps and two 100UF caps in the upper corner.
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OK I finally had chance to look at the board again. I've been over it with the multimeter again and it looks like the problem may be C506 (22uf 35v) as it is shorting to ground on the positive terminal. I've replaced it with a new regular leaded cap and it's still there.
Any idea what could be causing that?
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Maybe there is old cap leakage under one of the small ceramic caps or resistors in there area? Was there a bunch of leakage there prior?
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I did clean the area with IPA as I thought it could be something like that, but I don't remember seeing a lot of electrolyte there when I removed the original cap. There was a load of it in the audio area which I spent some time cleaning up, but everywhere else wasn't bad at all.
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There may be old fluid under some of the components on the other side of the motherboard. Look at the areas behind where the two 4.7UF caps are. Sometimes fluid can leak through to the other side of the board and muck up the connections for a few of the transistors.
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Gave it another really good clean and reassembled and I now have sound but no video. Reassuring to know that it does work, but I just need to get the picture back.
Any suggestions on why the video is not displaying - bad transistor somewhere perhaps? I guess it's the backlight that isn't working after all.
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I've read on here that faulty Q900/ Q901 can cause this so have ordered replacements! I'm not 100% confident as I can't see an image when examining the screen with a torch.
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Transistors replaced, all looked good...powered on and the fuse blew :roll: ](*,)
New fuses ordered...
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Think I found the reason for the fuse blowing, there was a blob of solder on the HuC6270 between pins 18 and 19. I've replaced the caps around the transformer just in case they were bad and removed the fuse in prep for the parts arriving tomorrow so we'll see what happens. :deadhorse:
Keith - thanks for your input so far :thumbsup: do you know what a good resistance value for VR500 would be? This is something else I need to check.
This was the short
https://i.imgur.com/h71KROj.jpg
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I'll have to check on the value for you.
One good thing about having sound is that if it is unable to be fixed with the stock screen, the system could be composite modded to work with one of the 3.5" upgrade screens.
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I'll have to check on the value for you.
One good thing about having sound is that if it is unable to be fixed with the stock screen, the system could be composite modded to work with one of the 3.5" upgrade screens.
I think that is going to be my only option now as there is no change to the screen after replacing the fuse. I tested my VR500 and it is showing almost no resistance and turning it changes nothing so I guess it's blown. Are there any known replacements for this? Might as well try that.
It's a shame as this GT is almost new, I bought it as new old stock in 2007 and have kept it that way until now. The shell is still mint condition so I will switch out the motherboard with a different one and get a screen mod done in an older shell I think. Browsing Buyee for a potential candidate as we speak!
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I'm betting there is a blown transistor on the board somewhere. This is usually the case when voltage isn't where it's supposed to be after a cap change. Look at where that cap gets its power from.
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Recently worked on an express with no video and only sound after a recap. Also no voltage at the 35V 22uf cap. I had to remove a number of components off of the motherboard, clean the board and components with isopropyl alcohol, and then re-install. I think one of the old caps leaked through to the other side of the board. I have circled the parts of the board I removed and re-installed again. I also marked(blue Dot) a Via hole short that I fixed by putting a cap lead through it and soldering on both sides. Might want to just re-solder the pins for one part at a time to see if video comes back before removing all of them and cleaning. I did this at first and got video back by just re soldering the legs for Q501 but then the video would start to fade until I worked on the rest.
(https://i.postimg.cc/0zr26RkR/img-1033.jpg) (https://postimg.cc/0zr26RkR)
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Thanks Keith, unfortunately the board now seems to be dead, no sound or any signs of life when powered on. Maybe I shorted something last time I looked at it, or whatever caused the original problem became fatal. I'm kinda sad about it but I do have another machine on the way over from Japan right now!
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Transformer might have gone bad. I just worked on another one that had old leaky cap fluid under the transformer shorting things out. I had to remove the grounding plate over it so I could clean it up.
Maybe just your fuse went bad, if not then most likely the main power transistor B1182. See if the transistor is getting power and if it's sending it out again.
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All is not lost! I replaced the fuse today and it is working again, minus display. I guess I hadn't checked it properly the first time around. I gave the board another really good clean and removed the transformer shield to clean under there but no dice. I do have some replacement Q500 transistors on the way so I will try replacing that and then give up.
So I will probably go ahead and replace the screen with a 3.5" I think. Are there any guides around for this?
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Here is how you get composite so you can use the new screen.
(https://i.postimg.cc/JHD8QGBM/pce-Composite-Video-repair.gif) (https://postimg.cc/JHD8QGBM)
It requires a bunch of work to be done to the HU6260 chip.
Here are the screens for it. https://console5.com/store/universal-3-5-composite-video-lcd-module-320x240.html
Here is the wiring guide for the screen. https://easyupload.io/j5ktf1
These things should really be backed up here so I'm not one of the only few with this stuff saved on his computer. Some of this used to be on Turbokons website but he has shut it down for now. Might come back later.
The composite work to the HU6260 chip can be a little confusing for some and risky since the pins can break somewhat easily if bent too much. I'll post a picture of the way I do it once I work on another one of these screen mods. I should be doing one within the next week.
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Thanks - I was searching around yesterday and ordered a bunch of stuff already - I got the screen and mounts etc from Console5. I found this board on OSHPark so I ordered some:
(https://644db4de3505c40a0444-327723bce298e3ff5813fb42baeefbaa.ssl.cf1.rackcdn.com/8a293264c0d2c4502dc115dd83e5fe49.png)
They had the one with the same layout as you posted but this one has AV Out so I assume that's why it has an extra transistor. Thought I might as well get this one since that could be an interesting mod.
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Yes, those boards will work. I didn't realize there were some on oshpark now.
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Quick sanity check - the 220 part on the board refers to a resistor, right? I have seen some boards with capacitors so I'm wondering whether that is 220uF or 220ohms?
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I've never used that board before but I feel pretty safe saying it's a Resistor. It's extremely difficult finding any 220UF caps that are that small in size(0805 Ceramic). What is weird is I don't see why there is a Resistor there though. 5V should be run to both Transistors. There is no need to have a resistor or capacitor in between them. The only reason may have to do with the type of transistor being used in the schematic. I always use a 8050 transistor.
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Interesting, I'm none the wiser on how it works even looking at the schematic.
Is there a reason nobody uses RGB for these? Is it due to a lack of compatible screens? Would a screen with a VGA input accept RGB from the PCE GT?
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It's because the only place that sells suitable RGB screens is out in Japan and they will only sell to a Japanese location. No overseas sales according to their website. So you would have to go through some sort of third-party company to get one. Not to mention they are actually sold out on them right now due to supply issues.
If it were easier to get RGB screens, then that would definitely be a better option because one wouldn't have to go through this work of getting composite enabled for the system.
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Oh so those would be the RGBDRV boards I've seen.
My wife is Japanese so we go there a lot, and she has family in Tokyo. Will see about getting some sent over when they are in stock again. We were due to be in Tokyo last month but the Covid situation put a stop to that :-({|=
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Another update. While waiting for the parts for a 3.5" mod I decided to have a play around with LED modding the original screen. This is usually not too difficult to do and I had a DMG Gameboy backlight lying around. After fitting it and wiring it up I tried it in the damaged GT and there's no picture :? So I tried it in one of my working machines and it worked fine.
The sound was a bit low for some reason so I decided to recap the machine again and it nice and loud now, but still no picture. I'm wondering if the 6260 is damaged? Or does the video circuit also depend on having a working backlight maybe?
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Price shining a light into the screen and see if you can see any video. You might also be able to see something if you look at it from an extreme angle off to the side or top. You should still be able to see something even when the backlight is out.
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Price shining a light into the screen and see if you can see any video. You might also be able to see something if you look at it from an extreme angle off to the side or top. You should still be able to see something even when the backlight is out.
Tried it, nothing. The LED backlit screen worked on my other PCE. It looks like I have a video issue on that board too :-k
Hopefully running composite directly from the HUC6260 will work otherwise this board is done.
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Composite should still work. Every time I've had audio with no video, the Composite and RGB still work from the 6260 chip just fine. Well, S-video as well.
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Damn, I wonder if my 6260 is fried.
Here is the LED mod running on one of my other GTs, it's not quite there yet, needs to be brighter and maybe some warmer LEDs, but I reckon battery life would be doubled or tripled.
Comparison with stock:
https://i.imgur.com/lWoBQ5m.jpg
https://i.imgur.com/XtRGC6N.jpg
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In case anyone one was curious, here is a pic of the Composite mod built from scratch.
The pins that needed to be grounded for the mod to work are all connected with an extra cap lead underneath the project board. I run the ground to pins 55/56 on the video chip since both are ground.
(https://i.postimg.cc/bGkdS0rW/IMG-20200703-063353.jpg) (https://postimg.cc/bGkdS0rW)
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I finally received the composite boards this morning, so I didn't waste any time and got one made up. About 3.5 hours later and...she lives! To my amazement it all fired up first try. I have a few things to tidy up, I like to use connectors rather than soldering direct from board to board so I need to wait for those to arrive, but at least I know everything is working.
https://i.imgur.com/N3MR1L0.jpg
https://i.imgur.com/DgHV1rh.jpg
I will post agin once it's all done and hopefully close this sorry saga with a happy ending. :D
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https://i.imgur.com/m7iEn7d.jpg
https://i.imgur.com/XfvpKja.jpg
What an awesome mod! Thanks for your help with this Keith.
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Mmm, that looks nice. Good job on getting 'er fixed up.
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Looks good!
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Congratulations, it looks stunning!
Ps
Where did you get all that minty Pc Engine GT goodness? :O
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Congratulations, it looks stunning!
Thanks!
Ps
Where did you get all that minty Pc Engine GT goodness? :O
Which one? I have 3 currently,
- boxed mint condition one I have owned for a long time
- Almost-mint non-boxed, came from Mercari Japan
- The one above with the new screen - Yahoo Auctions
I would recommend looking at these Japanese sites if you want one, they appear regularly and you can get some good deals. Good ones tend to be very popular auctions (a nice boxed one with some games and boxed accessories just sold for JPY 90,000 (£700/$840).
Ebay is not the best place, but occassionally you may find a nice one on there.