Turbo Duo doesn't power up

[ClodBuster]

Gentlemen, welcome back to the shop.

If you guys have any advice, even for the really obvious things, I'd be very thankful!





The current setup:




BM 235 connected in series between power supply and Turbo Duo for measuring current. Fluke 12E+ connected in parallel to measure voltage between Duo's ground and some points on the Duo's PCB. Please note the CD-Rom cables are currently not attached. The unit has beed recapped by somebody who I can vouch for that he knows what he's doing. The RGB mod and the region switch however look rather amateurish to me and have been done by the previous owner. Pic taken with the power supply being turned off.




Adjustable power supply. Able to deliver up to 15 V at 3 amps. Pic taken at no load.




A closer look at the power connector.




Let's flip the power switch to ON.




Mhm... that left power regulator is getting pretty hot. The right one stays cold as ice.




No wonder. That darn thing is trying to pull 2 amps. What the f*ck.




Look at the power supply to confirm what the DMM is saying. Yep, that's 20 Watts of angry pixies dancing merrily around the circuit.




Let's measure the voltage on the leftmost pin of the left power regulator.




8.5 V. I don't know if this is good or bad.


Oh well. Let's flip the power switch to OFF and examine the PCB.




Look at that component. I guess that's some cap which is a little bit "how-are-you-doing"? Or is he trying to say "look mommy, I can stand on one leg!"?




The underside of the PCB. The wires for the RGB mod are actually stiff single core wires instead of proper flexible multi core ones. I guess I'll have to replace them sooner than later.




A look at the soldering joints of that mischievious voltage regulator.






Addendum:




Some shop humor.



One ruler to rule them all!

[LowRes]

I'd start by replacing the left voltage regulator that seems to be getting very hot. 

Good luck! that was quite the write up with pics lol hopefully an easy fix

[ClodBuster]

Thanks! I'll do this ASAP. I'll also resolder that red capacitor.

I'll then start testing if the current draw and voltages are back to normal behaviour on the console.

If everything is alright and the console has come back to life, I'll do these things:

- Resolder the RGB mod with flexible leads.
- Use a modern RGB amp circuit with jailbar fix etc.
- f*ck that sloppy DIN video connector. I'll replace it with a SUB D 9-pin connector straight at the back of the console as per GameSX instructions.
- Get my hands on an old analog oscilloscope (a.k.a. "the brick") to troubleshoot the CD-Rom drive.


Thanks for stopping by. Keep your dick in a vice.

[mickcris]

I would check those tantalum caps as their failure mode can be a short.  Seems like you have a short somewhere on the board.
Also if you haven't already, check the voltage regulator that isn't outputting and make sure it's not showing a short to ground

[NightWolve]

Good luck!

[ClodBuster]

Thanks to both of you. I'll check for those faults as well, didn't know about that before.

[Necromancer]

Poor lil Duo. 

I hope you get 'er figured out and back to working like new.

[ClodBuster]

Today I ordered a pair of voltage regulators. In the meantime, I'll check the tantalum caps for shorts as suggested.

[ClodBuster]

One of the circular tantalum caps in the lower left area was missing contact to the black botch wire. Resoldered it.

[mickcris]

One of the circular tantalum caps in the lower left area was missing contact to the black botch wire. Resoldered it.

It works now?  or that was just one issue you found?

[ClodBuster]

Just one of the issues so far. It might have gotten loose due to repeated disassembly, just as with that one red rectangular cap near the CD-rom drive. The left leg of the red cap lifted some copper from the PCB, I'll have to do a botch wire fix to the next available contact point.

I haven't tried powering up the console in the meantime yet, though.

[ClodBuster]

I managed to resolder that red capacitor. Luckily, I didn't need a botch wire, I just needed to carefully scrape the PCB surface to get enough copper surface for the leg to attach.
Then, I put some paper between the PCB and the bottom metal shield, to prevent accidental shorts. I haven't replaced the voltage regulators yet.



The power supply now shows 10 V and a current draw of 0.45 amps.




Probing on to the fuse shows 9 V. There must be a 1 V loss somewhere between the power connector and the fuse. What the...




Still, probing around the board, including the voltage regulators, shows a voltage of 5 V. Bang on! Both regulators are getting slightly warm, but not hot. Probing the AV output shows voltage on the pins. Could it be...?




Needless to say, I couldn't wait to connect my Turbo Duo to the TV. Still powered by the lab supply, where the hell is my dedicated power adaptor brick? I've got no idea.
As you can see, the console has been brought back to life, and I spent some time playing Gradius and Peach Boy.

Thanks again to all you guys for your support and giving me confidence. You rock.



Final thoughts:
When putting the PCB back into the case, I'll have to see if there's any unwanted contact between the metal shield and some component legs sticking out.

[ClodBuster]

Well, once the plastic case is closed, there's a short again.

I'll investigate.

[Keith Courage]

Nice, that's one of those older style turn knobs for the region mod isn't it. I've never done one that way myself but always thought it was cool and interesting to see whenever someone sent me a console for repair with one of those installed in it already.

[ClodBuster]

Thanks, yes it is.

I've got some thin styrene sheet around that I will use to isolate the metal shield against the underside of the PCB.
Also, I will replace the stiff wires of the RGB mod with more flexible ones, hopefully this will help reducing stress on the components and less wires being ripped off whenever the console gets opened.