strange problem...need Turbo Express / PC Engine GT service manual

[KewlK]

Does a service manual exist for the TE or PCE GT?

Have searched the net and several forums extensively, no luck.

Aware of the one for the TG-16, but it would be of little help for the
specific issue I am trying to resolve (it definitely is not capacitor related).

Need to know which transistors are in direct control of driving lcd contrast.

The CFL and corresponding circuitry works properly...backlight completely fine.

Screen takes -several- minutes to reach an acceptable level of picture contrast.
During this phase, the brightness control wheel is useless (which actually adjusts
contrast rather than affecting the backlight).

All new quality caps properly installed and tested. Bizarre problem remains.
VR501 factory set to output 4.75v at the primary voltage regulator (good).

Keep thinking it's likely a failing transistor.

Any help or advice will be greatly appreciated. Thanks

[NecroPhile]

I don't recall seeing official manuals for 'em, but I'm sure steve/chops/keith/mnky/turbokon/etc. can help.  These guys have seen just about everything.... and fixed it. 

PS - Thread moved to repair subforum.

[MobiusStripTech]

There is no service manual that has been unearthed as of yet.

[KewlK]

Thanks for the reply. It would have to exist, or at worst did exist..but now lost. Maybe I'll try getting in contact with someone at NEC and also with whatever remnant of Hudson Soft there might be (post Konami merger). Hudson jointly collaborated with NEC during the development of all the PCE/Turbo related consoles, so there should be documentation from both companies for everything. Former approved service centers would have had all the documentation as well.

As you would know, the solder mask on the TE main board PCB is so dark, making traces very difficult to follow. It just makes it that much more frustrating in my occasional attempts to pinpoint the cause of the problem.

[wolfman]

Why dont you try and replace all caps? It still might resolve the screen issue you have...

[KewlK]

Hi wolfman. I already had replaced all capacitors as mentioned in my first post:

"All new quality caps properly installed and tested. Bizarre problem remains.
VR501 factory set to output 4.75v at the primary voltage regulator (good)."

Regardless, I had a crazy idea. Decided to do away with aluminum electrolytics entirely. I replaced all caps again...this time with solid tantalums. The new aluminum caps I pulled still test just fine, but curiously, the contrast problem is now completely gone.

The added benefits: This TE will likely never require a capacitor replacement ever again, no nasty electrolyte to leak and corrode pads/traces/ICs, extremely low ESR, great performance in a wide temperature range (they don't mind the cold); -Much more efficient than all other capacitor types resulting in...increased battery life, brighter screen, great contrast, and even louder volume.

Possible risks: If a short circuit or power surge were to hit the TE's mainboard. Tantalums are very sensitive to electrical faults. Failure mode at best is some smoke similar to a blown diode. Worst case scenario is actual flame or capacitor detonation. But consider that a major short circuit or surge would likely result in an unsalvagable unit anyhow. Very unlikely events regardless.

Tantalums get a lot of negative attention from fear mongers and those that misunderstand them. The reality is that they are simply the best capacitors available, still preferred by many mainboard and cell phone manufacturers...not to mention NASA. If sufficiently voltage derated and installed properly, any inherent risks are almost completely nullified.

I considered using ceramics, but their capacitance value must be derated to an insane amount to achieve acceptable performance. Also thought of dry polymer types and other hybrids, but their expected service life isn't long enough. Mica film caps are too expensive and overkill.

[MobiusStripTech]

Tantalum are also made with a rare earth metal which will only get more expensive with time.

[KewlK]

Yes, in addition to the metal's rarity, it is unfortunately also classified as a conflict resource. Their value has fluctuated wildly over the years. Kept track of the market looking for a good moment to pounce. Right now they are readily acquired at decent prices. I've bought several in bulk and plan on incorporating them into many of my projects.