REPAIR GUIDE - TurboDuo/PC Engine Duo/R/RX: Laser Swap & Adjustment Guide

[Drumjay]

I have a Duo at the moment that is causing problems. This fault existed before capacitors were changed. The fault is still there after all the capacitors have been changed. Will turn on no problems. Will load and play the Hu Card games fine. But removing the card and turning on all I get is a white screen. The interface is just not loading for the CD ROM part. I presume this is chip controlled? Does it mean the chip is dead? Thanks for your help.

[thesteve]

its either a dead chip or open connection to a chip
the 22uf caps near the slot are power filters for other sections of the system, check for 5V on them

[TheOldMan]

Do you have the cd system card in?

[TheOldMan]

My bad. Missed the part about it being a Duo.
Still, have you tried with a cd system card?

[Drumjay]

Thanks for the fast replies! I have checked all the 22uf caps 5 volt on every one. Typically my system card has vanished not in the box! Everything else is fine the laser and all the motors are fine checked in a working console. I also have another one that has the system start up but the laser will not move up and down, again I know it all works tested in a working one so there is something in between stopping the laser. Busy trying to change all the caps! But nothing yet. I have 4 in total but only one working at the moment. Quite frustrating!

[thesteve]

find my pinout for the DMA chip, and probe its system bus
odds are you will find a missing signal either there or on the D0-D7 pins at the slot without card

[Drumjay]

Thanks again. I will try that. Luckily I have found the system card and it works beautifully! So may as well just use it this way if it's not possible to repair the chip?

[thesteve]

works with sys card.......that narrows it down

[CkRtech]

Did a full cap replacement on my Turbo Duo and am gearing up to do my first laser adjustment. Out of the gate, the laser reads audio CD TOC, fires up the first track, plays well, and can track across the disk OK. That probably saves me a lot of pot tweaking.

It seems like the disc and laser might be making contact somewhere between the 30%-50% mark of the disc (inside ring being 0% and outside edge of disc being 100%). After getting a few tracks in, I can hear the disc making contact with something - which alters the rhythm of the spin.

If I track to the end of the disc, I can see what appears to be the laser either "bouncing off" of the disc or having major issues attempting to focus on the track. It spits out several seconds of severely distorted audio, and then returns to center.

I will probably attempt to tweak it today, but I welcome any thoughts from you guys that have done tweaks before. I haven't decided if I want to go to the trouble of hooking my oscilloscope up to it or not. 

[thesteve]

look for mechanical binding first

[CkRtech]

I made an error in my explanation. Instead of the 30%-50% mark being the entire range of the issue, it is actually the approximate starting range where the issue becomes noticeable - the worst being the 100% (last tracks on the disc). Audible laser/lens noise can be heard at about the 50% mark of the disc (smallest degree of focus struggle, perhaps?) The further out on the disc it goes, the more issues it has. If I test the last track, it starts bouncing one or two tracks back and skips a few seconds/chunk of seconds/minute or two forward/backward.

The gears and rods appear to transport the lens OK from what I can tell. I applied the smallest bit of white lithium (spray) to them last night, however I do not think it made a difference.

[thesteve]

that sounds like a pot adjustment to me

[CkRtech]

Seems slightly better. I still have some issues on the later tracks. The spin speed slows on the later tracks, and it seems like the cd gets a slight wobble (when viewed straight on from side of disc) when laser is on the outside tracks.

Thanks for your help.

[blueraven]

Glad to see its all going well! I have a DUO-R in the shop as we speak, and will be posting an update on the differences of the two units, and updating the links. Duo_R, could you update the photo links on Page 1? Much obliged!

Thanks Guys!

[cjameslv]

Many thanks to bluebmw for his guide on adjusting pots. After i finished replacing caps on my duo, the cd player still didn't work, so i figured i needed to adjust the pots. They were way out of whack! His guide got me dialed in perfect and everything runs great! Holy shit though, i had to hunt my ass off trying to find a music cd