Help! I have killed my PC Engine GT

[MasterofBiscuits]

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

[Keith Courage]

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.

[MasterofBiscuits]

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?

[Keith Courage]

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?

[MasterofBiscuits]

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.

[Keith Courage]

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.

[MasterofBiscuits]

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.

[MasterofBiscuits]

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.

[MasterofBiscuits]

Transistors replaced, all looked good...powered on and the fuse blew   

New fuses ordered...

[MasterofBiscuits]

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.

Keith - thanks for your input so far  do you know what a good resistance value for VR500 would be? This is something else I need to check.

This was the short

[Keith Courage]

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.

[MasterofBiscuits]

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!

[Keith Courage]

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.

[Keith Courage]

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.

[MasterofBiscuits]

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!