Turbo Duo doesn't power up

[ClodBuster]

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.

[ClodBuster]

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.

[ClodBuster]

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.

[ClodBuster]

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.

[ClodBuster]

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.