recapped Turboexpress no power

[wilykat]

From this thread: https://www.pcengine-fx.com/forums/index.php?topic=19511.0

I've cleaned and recapped and replaced the fuse. But when I powered it on, nothing happens.  No smoke, no light, no sign of life in the stock LCD. (no sound naturally since I am still without replacemen audio jack and sound doesn't get piped to speaker without the jack)  The meter shows it is drawing only about 20mA so something is getting through but something isn't working.

Now what?  I am guessing issue around the voltage regulator.  Someone has any detail or schematic on the power circuit?

[SephirothTNH]

Your big pic is gone now and I'm not very familiar with the turboexpress.  But if there are mlcc capacitors in the power section check to see if one is shorted.  If one is shorted they should all read shorted.  Then you just have to find the one that is actually bad.

[wilykat]

There's a fair number of SMD caps on TE including some around the power section.  I despise working with tiny pieces.

I'd have to check those tomorrow, got doc appt in the morning and I need to sleep.

[wilykat]

I cleaned the grey blob off the PCB that was covering the solder side with the power in jacks and switch. I am getting dead fish smell now so it seems one of the old cap leaked, got through a via and ruined connection somewhere under the grey blob.

I can't get 100% cleaned and I don't know what solvent to use to completely remove grey blob so it'll be hard to trace and figure out what is supposed to go where and which via is bad.

Not only was the last person very sloppy with recapping, he didn't clean thoroughly or even tried to remove the grey blob to clean and neutralize the fluid. I am willing to bet when I tried to power it on, it was only going through a few components and never reached 5v circuit.

BTW only 1 obvious power regulating SMD cap in the area, when I checked with my meter the resistance was rising until it reached infinity so it's probably fine.  There's about 20 or 30 SMD caps on this side.  I'll upload new pictures later.

EDIT: really fucking hard to figure this out with all those grey residue still stuck to the PCB. What idiot thought it was a good idea to pour stubborn grey glue on the PCB next to the battery connector and the 2 inductor coils?

[Keith Courage]

That grey stuff is inside all of them. Just scrape it off with a small screw driver.

[wilykat]

I got 99% of the grey crud cleaned off but I can't see any obvious problem other than the power in jack

https://i.imgur.com/wSxc2Ei.jpg

I can't see traces under solder mask which makes probing hard

[wilykat]

I tried checking what I could. Inductors all read 0 ohms, caps rose to infinity, transistor checked good. Still no power. Since I can't see traces and there are no schematic, there's no way to figure out where the power ends or why.

Guess this one will be gathering dust.

[thesteve]

check power at the switch
the power jack disconnects battery ground when used and could be dirty as well
check fuse often

[wilykat]

I plugged in power rather than using batteries contact, the TE came to life!  All I got were dim screen and adjusting brightness had no effect.  With no sound (broke the phono jack), I couldn't tell whats going on yet.

I still need to put in the audio headphone jack (still waiting on China) and I may need to recheck the caps. If I have to, I'll open my other TE and compare connections.

Also suggestion on cleaning the power jack? Or should I replace it?

[NightWolve]

I did have to replace the power jack on mine. It was flaky to the point of moving the unit just a little bit and it'd disconnect, so I found a more stable one and never had a problem again. Point is, those jacks weren't designed well IMO so you probably might have to replace it anyway, but obviously this unit has a lot more problems to begin with... :/