Handheld Hijinks Vol 7 - The PC Engine GT
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22-01-2024 4:48pm#1
An uncommon handheld, the PC Engine GT packs all of the power and might of the PC Engine into handheld form - complete with 90's (80's really) era LCD tech. A bit like what the Nomad is the Megadrive, the PC Engine GT lets you play full sized Hu Cards on the go. This unit unfortunately isn't mine, it belongs to @Quigs Snr who asked me to take a look at some issues it's having.
1) First thing's first, any of these on original capacitors need them changed pretty urgently. They're very prone to leakage, so that's task number 1 here.
2) The controls don't work. Well, buttons 1 & 2 don't work, along with the turbo fire sliders.
3) There's no sound at all.
Lets dive in & see what the story is so...
^^ Pretty minty unit it must be said. It's also quite a nice design, simple, but has a good quality to it.
^^ Quick power on test to verify the issues...
^^ Yep, no sound, no controls either.
^^ Ok these things aren't going to win any awards for resolution any time soon, but still, it works exactly how it should, and how it did when released. There's value in that alone!
^^ This thing would challenge any of the big hitters as battery killers. 6 AA's!
^^ Split the unit in half, and we're in. Need to remove the mainboard next.
^^ Tiny little thing, mad to think this is basically a full sized PC Engine (which in themselves are tiny.)
^^ Ok, looking at the caps that were in it....there's no leakage, which is good. They look a bit odd though, if I didn't know better I'd say one or two were changed before. They don't have a factory finish to the solder, but some of them look too good to be hand soldered either. It's obviously best to go on the basis that they're original, and replace them all as a complete set. At least this way, we know it's had a full and complete recap.
^^ Full set of replacement caps. Two problems jump out at me, which I'll go into below....
^^ The shielding on both sides has to be removed, which is a little tedious. Some of the solder points are hard to reach, and even sit under the opposite shield.
^^ New cap is a lot bigger than the one that's soldered into place here. It's not a problem, as the pads can accommodate the larger size.
^^ Hot air gun makes this fairly straight forward. With some patience, and even heating, the old cap slides right off.
^^ The pads are then wicked clean, and mopped with some IPA to make them new & shiny again.
^^ Same treatment for all existing caps, all pads wicked, and all cleaned with IPA. This gives a nice clean base to work from with the new caps.
^^ Problem #1 with the new cap kit. It wants me to fit an SMD type cap in place of a through hole one.....eh, no thanks.
^^ Looking through my spares, I find a 470uf cap that'll do nicely. It's rated for a higher voltage, but that's absolutely fine.
^^ I work my way around the board, and replace all the SMD caps. So that's the main unit fully recapped. Next is the controller board.
^^ Problem #2 with the new cap kit - it doesn't provide a cap for the controller board. Sloppy stuff! I'll have to go rooting in my spares again...
^^ I give the underside a thorough clean with IPA, in the hopes that sorts the controls. There's quite a bit of residue let on the q-tip.
^^ A quick reassembly, and time for testing....
...aaaannnnnnd......nothing. White screen. Balls. Remind me why I do this type of thing again?!
^^ After much fault finding, disassembly, desoldering, tracing with the multimeter, and head scratching (and I mean much!), I found the problem, this little bo**ox of a solder blob somehow made its way onto the legs of this chip and was pulling them to ground. I removed it with iron, and tried testing again....
^^ Ok, phew, it's working again...thank god. It's always more worrying when working on consoles belonging to other people! The bad news though, is that the sound, nor the controls are working. So it's obviously not a dirt or capacitor issue....more diagnosis required.
^^ At first I though it might be the turbo sliders not making contact properly, thus disabling the buttons. I straightened the pins in order to make better contact. No joy though, the problem remained.
^^ Then doing some digging, I put two and two together. This is a single sided PCB, so these black bands are conductive strips than run over the top of the pcb traces.Is it possible they've degraded over time? In the above image, you can see where I've exposed the trace on one side of the strip, and I've a test point on the other side....there SHOULD be continuity between the two points I've circled in white, but there isn't....that has to be the problem!
^^ I bypass the conductive strip with some enamel wire, and try testing....
^^ Nice! It now works, well enough for me to grab a quick Perfect on Ryu! Button 1 and II now work, but the Turbo slider buttons don't, so more diagnosis needed!
^^ Same test again here. I've exposed the trace at both ends, and I'll try a continuity test. This is a common trace for both sliders, so hopefully this is it! There's no continuity between the two points, so that's a good sign.... (You'll see here the eyelet for the replacement capacitor came away from the pcb when I was changing it. Standard enough fix, expose the pcb, and solder the capacitor leg to the pcb - continuity check shows that's perfect now.)
^^ Conductive band bypassed, time to test (again!)...
^^ It works! All buttons and turbo fire work perfectly now....this image proves it! (Ok it doesn't, but you'll have to take my word for it!)
^^ Next up was the sound issue. A safe bet is a faulty headphone jack disabling the on board audio, so I desoldered it and removed it for cleaning.
^^ I tried some electrical contact cleaner in the mechanism, and cleaned all of the pins. Unfortunately, this didn't work.
I then tested anything else I could see, continuity testing the ribbon connector, double checked soldering of the capacitor etc. So I'll have to admit defeat for now on this one. I recommend a replacement headphone jack and go from there, because there are some erroneous readings from it.
https://www.retrosix.wiki/audio-circuit-pc-engine-gt
According to this, with headphones disconnected, I should be getting continuity between pins 6 & 7, which I don't. When there's no connection between them, it's the signal to deactivate the speaker, and use headphone audio instead. I did try bypass this and connect them with a bridging wire, but it didn't help. There's also only audio from one side of the headphones, so at this point, I'm inclined to think it's the jack has broken down internally.
So for now that's it, there may be a Part 2 in the future, hopefully one that shows an audio fix!
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Just coming back to this yesterday morning, armed with some info I'd found online about bypassing the headphone jack.
^^ I desoldered the jack again, and bypassed it via the pads themselves. I'd done this previously, but with the jack still in place which is why it didn't work.
And, yep, the sound burst into life. Not a bad sound from the unit at all, all things considered! Great, this confirms it's the jack itself then. I can either fit a replacement (which you can get, but a lot of info online suggests you've to file the shell ever so slightly to fit modern versions, which is far from ideal.) Or, I can try repair this original one, so let's try that.
^^ First up was a good old chipper bath (aka, salt & vinegar.) 30 mins in this solution will help break down and loosen any built up crud inside the mechanism.
^^ After 30 mins in the above, it takes another 10 mins inside an IPA solution. This will dissolve any vinegar left inside, and clean any final contaminants.
This alone didn't work to fix the issue. I could still tell via the multimeter that the jack was not bridging the correct pins with nothing plugged into it.
^^ Opening the jack, you can see the lever arm from the front piece slides a slider on the rear piece, bridging the middle and top pins. This isn't correct for an empty jack, it's supposed to return to the middle, causing the slider to move down and bridge the middle and bottom pins on the end piece. This is how it should be WITH a headphone jack connected. There must be a spring missing.
^^ I can manually move it down myself, into the correct position for an empty jack. However, as soon as I plug headphones in, the slider moves back up (thus disconnecting the on board audio.) Without spring tension, it'll stay this way too.
^^ I found a small, non-conductive spring that I was able to cut down to size (thank you Mr. Pen)....which fits inside the housing, and keeps pressure on the slider arm. This way, the pressure will keep the arm in place when there's no jack in place (thus keeping the sound on.) It'll allow headphones to be fit too, and I get stereo audio from them also. The only thing it fails at now, is that it won't disconnect the internal audio when headphones are inserted.
The owner is happy enough with that, as it means we don't have to risk filing the shell for a replacement jack. So yeah, that concludes the thread. A now fully working PC Engine GT, complete with controls and sound!
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