Need help with repairing a PC Engine GT

Started by Macross_VF1, 11/19/2018, 07:47 AM

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Macross_VF1

I recently went through my entire collection of consoles and computers to see what worked or not. Unfortunately my PC Engine GT is one of the casualties of time. As I understand it, the problem is not uncommon. The machine powers up but only shows a black screen with the backlight on. No amount of jiggling with the Hucard gets a response. I've taken apart the system and found at least two capacitors that seem iffy. While these probably need replacement, and indeed the rest as well, are they the direct culprit for the problem I'm experiencing?

Here's a link to some pictures of the two caps that I'm talking about.

IMG
IMG
https://imgur.com/a/6OJ3ZZi

Keith Courage


NightWolve

Yep, full capacitor replacement time! Don't be cheap, remove every one, clean off the leaked electrolytic fluid very well, and replace with fresh ones. Hope that the fluid didn't damage/corrode any trace, via, etc and you might be able to get it up and running again with just some basic soldering skills. :)

Macross_VF1

It is as I feared then. I have some basic soldering skills but this might be beyond my expertise. Everything is so tiny! Also, the caps I have are way bigger, anyone know if it's possible to get a similar type to the ones used in the machine?

NightWolve

Yeah, Digikey can sell you surface mount models like what's there but everybody would recommend to switch to the regular ones since they're easy to desolder if you ever have to do it again and they're bigger, better, will last longer since more fluid, etc.

Macross_VF1

So I've started replacing some caps and the machine works again (yeah!). However I immediately discovered that the sound is gone as well (booh!). This unit truly need a full recap. I have ordered new soldering stuff, particularly a better soldering iron so I should be able to save this unit.

dshadoff

Has anybody here done a recap using tantalum capacitors (instead of the oil-based ones) ?
Theoretically, they should have a better lifetime - and if/when they do fail, they wouldn't leak anything out causing other issues on the board...

Macross_VF1

#7
Quote from: dshadoff on 11/22/2018, 10:33 AMHas anybody here done a recap using tantalum capacitors (instead of the oil-based ones) ?
Theoretically, they should have a better lifetime - and if/when they do fail, they wouldn't leak anything out causing other issues on the board...
I've been thinking along similar lines. Basically I was wondering why no one has come up with better capacitors, as they should have changed and evolved over the years just like every other type of tech. If these tantalum capacitors are better how come no seem to be using them? Or are they just that much more expensive?

Anyway, back to my GT, something that stands out on the circuit board are several areas covered with a grey or white blob of... something. I'm assuming it's there to protect delicate parts of the board but it's seriously hindering my soldering efforts in places. Any suggestions what it is and how I can remove it?

dshadoff

Quote from: Macross_VF1 on 11/22/2018, 02:48 PMIf these tantalum capacitors are better how come no seem to be using them? Or are they just that much more expensive?
Yes they are more expensive - but not enough to make your eyes water (or at least weren't the last time I looked at prices).
Probably worth it if you fear doing another replacement in another 5-10 years.

Sorry, I don't know about the grey or white blob you see...

NightWolve

Quote from: dshadoff on 11/22/2018, 10:33 AMHas anybody here done a recap using tantalum capacitors (instead of the oil-based ones) ?
Theoretically, they should have a better lifetime - and if/when they do fail, they wouldn't leak anything out causing other issues on the board...
Yep, "thesteve," our professional resident electrical engineer has!

Below is a TurboExpress PCB he used a mix of tantalum and also ceramic capacitor replacements on (although I have less trust for high uF value ceramic):

https://www.pcengine-fx.com/forums/index.php?topic=3249.msg273031#msg273031
https://www.pcengine-fx.com/forums/index.php?topic=10167.msg182962#msg182962
https://www.pcengine-fx.com/forums/index.php?topic=11660.msg223168#msg223168

IMG

A key discovery he made is getting rid of the hum in the audio of a Turbo Express. I dunno if you ever noticed that, it's more blatantly obvious if you use headphones and pause a game, you'll hear a pretty significant hum which was widely enough known among PCE/Turbo fans.

Steve said you could only target the 4 power related capacitors with just tantalum to also get rid of it, but I feel it's all risky if you're not a pro and don't really know what you're doing with no understanding of the physics...

The different behavior could cause problems as it did for me when I tried all ceramics on my SNES, the Composite amplifier circuit went crazy, it worked normally again only with original electrolytic capacitors, so beware when moonlighting as an EE... :wink:

Quote from: thesteve on 09/10/2012, 09:03 PMyes a full aluminum cap replacement is in order.
you can use aluminum, ceramic or tantalum caps as replacements.
note the 10uf smd cap to the right of the switch will also kill video
He seems more trusting, but there you go. He's always willing to give Pro-Tip advice in PMs if you message him.

Quote from: Macross_VF1 on 11/22/2018, 02:48 PMIf these tantalum capacitors are better how come no seem to be using them? Or are they just that much more expensive?
Yeah, they're more expensive as Dave said. They have different properties, which Steve has mentioned on occasion like less resistance to ripple current. Your Turbo Duo has them on the underside/bottom of the PCB, no known reports of failure, while the topside is mostly the electrolytic standard as expected.

Macross_VF1

It's great to hear that you have an expert on hand when you need it. I suppose he would know how to remove those blobs I mentioned earlier.

NightWolve

Quote from: Macross_VF1 on 11/25/2018, 03:34 PMIt's great to hear that you have an expert on hand when you need it. I suppose he would know how to remove those blobs I mentioned earlier.
A hot air gun to soften it a bit perhaps and very careful use of a razor blade. That's about the only technique I ever heard of/seen.

Macross_VF1

And it's alive! Oh the repair certainly wasn't easy and it is pretty damn ugly in places so I doubt it will survive another repair. However that's not important, it's back from the grave! Thanks for the help you guys and I'll probably be back later with a pair of PC Engine Duos that needs servicing.