Turbo Duo doesn't power up

[ClodBusted]

My Turbo Duo, which has been fully recapped last year and gave me hours of fun, does suddenly struggle powering up. Not even the LED lights up when switching the system on.

I've checked the power supply for faults. It's a Goobay universal power supply ( http://www.premium-cable.de/Goobay-Netzteil-stabilisiert-flach-ACDC-5V-6V-7V-8V-9V-10V-11V-12V-5200mA-60W_p5921_x2.htm ), the output is set to 10V DC with the correct pin assignment. No trouble here.

Last time my console refused to work, I did a simple case reassembly to fix it even if I couldn't locate the root for the problem. Maybe there was just a bad solder joint somewhere?

I'll repeat the same, but I would also like to know if there are any signs to look out for once I got the console opened up.

[Keith Courage]

First check the fuse. If that is good then check the two 7805 voltage regulators. Every common for one of these and or both to go bad. Do you own a volt meter? That's the best way to see if they are working.

[ClodBusted]

Thanks for your reply. Yes, I got a Voltmeter, this is how I tested if the power supply still had 10V output.

I'll see if I can get any useful readouts from the 7805's after checking the fuse.

[ifkz]

Look around for cold solder joints at the usual places:
=On the Duo, there is the small PCB board that the power supply end plugs into.  If I were having power issues, I would just touch up everything on that tiny board with new solder.  Suck off the old, add new (reflow), piece of cake!
=Reseat the cable that connects to the motherboard from this tiny board.
=Lastly, I would reflow each of the 7805's legs.  They (x2) generate a lot of heat, and I would think the legs could have fractured the solder over the years.  After all this I would see if it is any different and then pull the meter out.

Once, I was refurbishing a first model Playstation (the one with the built in composite on the back) and it had a cold solder joint at the power pin that was preventing it from even powering up.  Usually the fault is itermittent, like you describe, but this was completelty stone dead.  It took 5 minutes to get it up and running (and a donor PS One drive to make it functional).

I hope this helps, it is really a quick job once you have everything disassembled.  Not hard at all, even if all you have is a non-temperature controlled $7 wand    I haven't had this particular issue yet, but I hope these tips get you going again.

[ClodBusted]

Surely they'll do! Time to fire the Weller up again. Good thing these components are rather easy to reach, unlike the caps. I'll let you know if I had success.

[ifkz]

Now that I've taken one apart and really worked on it, I have nothing but respect for NEC's engineers.  It is a really nice system to work on, everything is easily replaced if needed.  Good that you have a Weller, you'll go far 

I'll keep an eye on this thread, good luck!

[ClodBusted]

So, the system is now open again and one of the first things I noticed was one of the wires to the AV port was loose. Congratulations to the previous owner who did the RGB conversion with a screw-on type DIN socket to the plastic case instead of using one that solders directly to the PCB. Nice botch job, every now and then I see wires coming loose from the pins, I'm kind of used to that look now.
Time to remove that PITA DIN socket and rather screw a DB9 socket to the rear of the console, just a la GameSX.

Unfortunately this wasn't the root of my Turbo Duo's problem.
The fuse is fine. One of the regulators (the left one) heats up excessively, while the other one stays cold. When I got the PCB out of the case and looked from the underside, I could see that the small solder joints from the "cold" regulator are looking suspiciously small and flat. Too bad I couldn't measure any Voltages directly from them, since I needed to unplug the main PCB from the small power inlet PCB to get it flipped.

I would really like to re-solder anything in that area, but at first I need to buy some more tin-lead solder tomorrow. Maybe I'll also try again getting any further measurements.

[ifkz]

Sounds like you are well on your way to a healthy Duo 

[BlueBMW]

Wellers are good... I do really like my Hakko FX-888 tho ;)

[Bernie]

I prefer hair dryers myself.  Nice blast of heat.

[ClodBusted]

Just a humble WHS40. Nothing special, but at least it lets me use different types of tips.

@Bernie: Lol, I heard about that story, but never saw pics.

[pulstar]

Wellers are good... I do really like my Hakko FX-888 tho ;)

The Hakko is really nice in my opinion as well.

Clodbuster, looks like you've found the area where the problem is. Hopefully it's just a dry joint and a quick reflow will sort you out.

[ClodBusted]

My poor 40 W iron isn't really up to the task of resoldering the big 'ole heat sinks, but the 7805s themselves got new solder now. I saw that the black wire at the small power input PCB wasn't attached to anything. I assume it should be attached to ground like seen on this picture:
https://www.pcengine-fx.com/forums/index.php?topic=3249.0
Funny enough the Duo worked for months without the wire being attached.

I also saw my Duo is missing the HuCard metal cover, since I got it region-modded from the previous owner.

Let's see if I can get it back running tonight.

[ClodBusted]

Blast from the past.

In the meantime, I upgraded the electronics equipment of my hobby room to a Weller WS-81 soldering station, a Voltcraft LPS1153 15V/3A adjustable lab power supply and two DMMs (EEVblog Brymen BM 235 and Fluke 12E+). Makes working on electronical doodads much more pleasant than before.

Last night, I started troubleshooting on my Duo again. I set the power supply to 10V and limited the current to 1A max, and hooked it up to the Duo's power input.

I double-checked the voltage and current flow by hooking up one of the DMMs in parallel and the other one in series. Voltage was fine, but there was no current flow shown, neither on the lab power supply nor on the DMM.

Then I unhooked one of the DMMs to check for voltage between GND and some points on the Duo's PCB. The fuse was fine, it showed 10 V DC. However, the power regulators did not show any voltage. They weren't heating up, too.

Strange. I will go deeper into troubleshooting in the next days.

[ClodBusted]

Rookie mistake. Before measuring, I should have flipped the power switch on the Duo.

D'oh.

Well... There are still some odd things going on that I need to sort out before continuing with the repair work. I'll let you know then.

[ClodBusted]

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 fuck.




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

[ClodBusted]

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.
- Fuck 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!

[ClodBusted]

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

[NecroPhile]

Poor lil Duo. 

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

[ClodBusted]

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

[ClodBusted]

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?

[ClodBusted]

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.

[ClodBusted]

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.

[ClodBusted]

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.

[ClodBusted]

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.

[ClodBusted]

I'm making good process on replacing the RGB mod wires. I was afraid of it at first, but now I'm even able to solder them to the legs of the graphics chip.

[ClodBusted]

Looks so much more tidy now with the new flexible wiring on the AV port. I also took the time to clean the PCB from the brownish flux residue using "Kontakt LR" flux remover.
I've now found the cause for the shorts. Do you see the black wires near the tantalum caps in the lower left? Just where they go down the PCB to the underside, their PVC coat is slightly worn. Thus they are just ever so slightly touching the metal shield once the PCB sits on the screw mounts.




Using a Proxxon Micromot 50/E, I cut away a portion of that metal shield and sanded it.




The black leads got additional isolation using elec-chicken's tape.



It werkz!




I tried both Hucard and CD games. They play fine, BUT there is one issue left.

The volume for Redbook CD-audio is pretty low. Either I've managed to damage one of the caps, or there is a potentiometer for turning up the CD-audio volume. Please let me know what you guys think I should look for when examining the board next time.

[ClodBusted]

Since the red 3.3uF / 50 V cap near the CD-rom drive got a slightly damaged case when I resoldered it in, I decided to replace it with a simple radial electrolytic capacitor of the same rating.

Still, the redbook audio streamed from CD is weak in volume compared to sound effects and chiptunes.



Guys, please let me know what I can do. Remember, this is a fully recapped Duo, so I'd rather look for the components that are in the redbook audio signal path, instead of doing just another recap.

[MNKyDeth]

Not sure if it would help. But you could go after the OKI 5205 (IC 502) and IC 505.
If I remember the IC 505 is analog and IC 502 is digital.

Currently sold out at console 5. Might need to hit ebay.
https://console5.com/store/m5205-oki-adpcm-speech-ic-for-turbografx-cd-turboduo.html

IC 505
https://www.ebay.com/itm/5PCS-M51131L-New-Best-Offer-2-CHANNEL-ELECTRONIC-VOLUME-BALANCE/322911670659?epid=21010585405&hash=item4b2f091183:g:8QEAAOSw3fZaHOMv

I however think a lot of the issue is with the voltage at the op-amp at IC 506.
IC 506 voltages for normal audio levels that I have seen is.

1 = 3.64
2 = 3.64
3 = 3.64
4 = -.5
5 = 3.64
6 = 3.64
7 = 3.642
8 = 7.29

Granted they can be off slightly from these values. But if all the legs on this op-amp are correct around these values then I would go after the two above mentioned chips if you still have low audio.

[ClodBusted]

Thanks.

These are the readings _without a game_ inserted. Do I need to do another check with a Hucard inserted? Shouldn't be a big deal. However, I'll run into problems when having to do the check with a CD inserted, as I don't know how to probe on the ICs with the case closed.

Hope this helps.

IC 502 (OKI M5205):

Pin	Voltage (V)
1	5
2	0
3	5
4	0
5	0
6	0
7	0
8	0
9	0
10	2.5
11	0
12	0
13	5
14	2.5
15	5
16	2.5
17	2.5
18	5

IC505

Pin	Voltage (V)
1	7.76
2	3.23
3	2.98
4	5.53
5	7.7
6	0
7	0
8	4.97
9	0
10	2.75
11	0
12	5.53
13	2.97
14	3.24

[MNKyDeth]

I'll check the voltages on those two chips tonight. I'll either edit this post or make another one.

Company for a b-day party at the moment.

[ClodBusted]

You are my hero.

[MNKyDeth]

Instead of putting 0 I put whatever I see on my multimeter. Or describe what it is doing. I tested with the board powered on. Not connected to the cd-rom and no HuCard in the system.

IC 502
5.05
0.3
5.05
0.7
0.7
0.7
0.8
slowly rises
0.3
2.548
slowly rises
0.3
5.02
2.527
5.04
2.521
2.521
5.05

IC 505
7.33
2.998
2.729
5.4
7.21
slowly rises
-0.2
0
-0.4
2.692
-0.4
5.41
2.745
2.969


From what I can tell they look pretty close to yours.