Hi, first post here. I recently purchased a PC Engine Duo that would "not play disc games". The system itself works fine via composite out and there's audio through the headphone jack. The laser would not move on the rails or make any noise. I owned a TurboGrafx-16 as a kid and always thought the Duo systems were really cool.
I did a full cap replacement and replaced the laser with a new HOP-M3 unit. Once that was done, I tested with a legit copy of JP Valis IV and a retail audio CD from the 90s. Neither of the discs appeared to be recognized ("Please set disc") but the laser unit would jiggle a bit after hitting Run. The rails are lubricated using some of the excess from the old HOP-M3. The motor that moves the laser along the rails works properly - it spins indefinitely if I remove the gear that actually moves the laser towards the "stop" switch.
I then cleaned the pots with electrical contact cleaner. With the power off, I then measured VR102 and VR104 with my measuring tool and I could get values of 1-10k Ohm on VR102 and then 1-20k Ohm on VR104, respectively. I do see voltage going into the CD unit with the main power turned on (after hitting Run); 3v, 3v, 10v, 10v from left to right.
I tried adjusting the pots using the guides on the site (mainly VR102 and VR104), but neither caused the CD to spin. From what I understand, the CD will not spin until the laser has focused on the CD (please correct me if this is incorrect). I tried adjusting a few degrees at a time on VR102, hit Run, waited, reset the unit via Start-Run, rinse, repeat. I then reset VR102 to 1k Ohm and tried with VR104. No change, still get the "Please set disc" and the CD does not spin. I don't have the magnetic "cap" from the lid in place, I'm not sure if that makes a difference?
When the laser unit jiggles a bit left-to-right, I don't hear the laser attempting to focus or move up/down vertically like on a PlayStation 1 - I assume this is because it's all done by hand via the VR10x pots? The only thing I hear is the initial jiggle. The unit does reset itself to it's initial state (far left) if I move it down the rails away from the small "stop" switch. The same thing happens when I swap out for the old HOP-M3 unit. Continuity seems good between the board and the HOP-M3 connections.
Any suggestions as to how to proceed from here, or what to test to confirm everything is operating normally?
Random aside: I've seen references to IC105, IC106 and IC501 failures.
Thanks for your help!
edit: One thing to note - At no time do I see a reddish light coming from the laser lens itself. The laser lens always appears to be clear. I've checked visually and using my phone camera (in case there was a refresh rate/low light level that my eye couldn't detect).
edit 2: I found a post mentioning that the laser unit should be trying to focus on the CD. My unit doesn't ever try to focus on the CD (moving the laser lens vertically up-and-down). It just wiggles left-and-right quickly on the rails and stops. I also don't see any light coming from the laser at all. This suggests to me that maybe one of the ICs is bad? Is there any way to test IC105, IC106 and IC501 with a multimeter? I don't have an oscilloscope, unfortunately.
edit3: I do see 5v on pin1 of IC501. Not sure if that means anything. I've gone through and cleaned any corrosion, including underneath the card slot.
EDIT 4: 12/01 update; The system works perfectly after fixing R199 and replacing the two BA6290. Prior to replacing these, the system was washed in soap/water. I also applied lithium grease to the CD lens rails. The system now runs stable and really well. I ended up 3D printing a replacement HuCard door since mine was missing.
