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Post by stirlingsteve on May 15, 2023 14:34:28 GMT
Hi all, new to the forums and am looking for a little "what would you do" advice. First, a little background. I've recently acquired a lovely Japanese PC Engine Duo which I know has never been opened and was therefore likely in need of a recap. It fired up to the boot screen fine but when I tried it with a HuCard, there was no sound (which I was expecting) and when I tried an audio CD, it span up fine but didn't get any further than that, which I wasn't expecting. Unfortunately, I don't have any CD games yet so I don't know how it would fare with one of those, but I figure if it doesn't fire up to the Audio CD menu then it's not going to be any better with a game!
I opened it up and could immediately see significant cap leakage but thankfully, very little (in fact no) board rot so clearly it's come to me just in the nick of time. The CD ROM unit looked a little grubby but otherwise OK. With no CD in I could see it moves the head to the centre as expected, then bobs a few times when trying to find a CD too, so outwardly all looks fine. As I said before, it spins CDs up as well, but seems to have trouble focusing or something, although I am no expert. I can see a very tiny red glow if I look at the lens from an angle with no CD in place which I think shows the laser is working, but I can't vouch for whether it's as strong as it should be because I don't know what they should look like when working.
I decided it was best to leave the CD ROM unit alone until the caps had been replaced, in case they were causing CD issues as well. I have since completed the recap (using quality like-for-like SMD and through-hole equivalents throughout), including the supercapacitor for memory backup and I'm happy to say the audio is back and the visuals are perfect. Sadly though, there is no discernible improvement with the CD ROM at all. So now I think either the original laser has given up the ghost, or it's in need of a retune via the dreaded pots. I have read up on how these units can be adjusted but at the moment, the pots are all unmolested and factory-set so I don't really want to touch them unless it's absolutely the last resort. So this finally leads me to the questions I have for you lovely people: What would you do at this point? Would you assume the laser is on its last legs and source a replacement now, in the hope that it'll work straight out of the box with the factory pot settings or is it worth risking those settings now and fiddling with the old laser to see if it'll work? I'm reasonably competent with a soldering iron and I do technically own an old Oscilloscope but I don't really know how to use it so I'm terribly frightened of messing with those pots unless there is literally no other option. 1) Do CD lasers commonly die over time? Is there any chance this one can be resurrected?
2) Is there any hope of a new laser working with the pots as-is or would I need to tweak them regardless? If so, is it worth breaking out the scope first? 3) Where would I be best finding one of these HOP-M3 lasers? Ali-express seem to have some but that's about it.
4) Does anyone fancy holding my hand? I'm scared... Cheers in advance for all your support and advice!
Steve
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Post by dshadoff on May 15, 2023 16:34:57 GMT
This may not answer all your questions, but hopefully it gives some more context (and may answer some of your questions)... I found a Youtube video on performing similar fixes to what you describe, and reviewed it to check that the guy is giving good advice and knows what he's doing: It's in 2 parts... www.youtube.com/watch?v=7l3lV0lYx2Uwww.youtube.com/watch?v=ak_v_ixuZCE |
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keithcourage
Punkic Cyborg
https://www.facebook.com/turbografxfan/
Posts: 220
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Post by keithcourage on May 16, 2023 11:13:10 GMT
If a capacitor change doesn't fix the CD drive then try turning the V102 pot counter clockwise slightly.
if that doesn't fix it then there could be damaged traces or via connections to some of the capacitors or the lens itself is bad.
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Post by stirlingsteve on May 16, 2023 14:41:05 GMT
This may not answer all your questions, but hopefully it gives some more context (and may answer some of your questions)... I found a Youtube video on performing similar fixes to what you describe, and reviewed it to check that the guy is giving good advice and knows what he's doing: It's in 2 parts... www.youtube.com/watch?v=7l3lV0lYx2Uwww.youtube.com/watch?v=ak_v_ixuZCECheers for the links, I've actually already seen these though - he's lucky in that his unit reads discs whereas mine won't read anything. Thanks anyway!
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Post by stirlingsteve on May 16, 2023 14:45:54 GMT
If a capacitor change doesn't fix the CD drive then try turning the V102 pot counter clockwise slightly. if that doesn't fix it then there could be damaged traces or via connections to some of the capacitors or the lens itself is bad. Yeah, I've been reluctant to touch the pots but do you think it's safe to try this before going for a new laser? What are the chances that the old laser needs replaced anyway? I don't know if they deteriorate over time or not really.
I'm worried that by messing with the pots now, I might make things more difficult for myself later on if I end up having to go down the new laser route.
Any thoughts on where best to get a new laser by the way? All I can find are some dodgy looking AliExpress pages like this one:
Cheers for the advice so far  |
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Post by stirlingsteve on May 16, 2023 15:51:09 GMT
If a capacitor change doesn't fix the CD drive then try turning the V102 pot counter clockwise slightly. Actually, I was reading on some other pages relating to these pots and everyone's been posting their resistance figures so I thought I'd do the same:
VR101: AB 5.63 - AC 13.3 - BC 17.66 VR102: AB 7.59 - AC 7.95 - BC 10.56
VR103: AB 16.83 - AC 4.71 - BC 19.97
VR104: AB 17.03 - AC 4.14 - BC 20.14
VR105: AB 0.3 - AC 0.35 - BC 0.35
I guess now that I have these numbers noted (and if I mark the pots), I should be able to return them to where they were easily enough anyway so I might as well bit the bullet. I'll let you know how turning V102 goes Ta so far!
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Post by stirlingsteve on May 16, 2023 16:13:23 GMT
Well that was quick! It's now happily playing an audio CD after just a few wee tweaks of VR102 like you suggested Keith - fantastic! It was skipping a few times at first but I turned it a wee bit further counterclockwise and it seemed to get more stable. Visually, I'd say it's moved maybe 20% round. I've left it playing to see if it gets right through the disc without skipping now but once it's done, I'll re-measure the pot to see what its new values are. I guess it might need a bit more adjusting but I'm just pleased it's playing something!
Sadly I have no game CDs yet, just a HuCard but I might go see if I can burn something and give that a go too.
Thanks again for the help and I'll be sure to post an update ASAP.
Cheers!
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Post by stirlingsteve on May 16, 2023 21:42:30 GMT
JUst a quick update, I found an ISO and burned it - it works too so I'm very happy! VR102 is now set to 3.55, 3.55 and 10.51 which is very different from before but it seems to be fine so I'll take that. Thanks again for the help!
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keithcourage
Punkic Cyborg
https://www.facebook.com/turbografxfan/
Posts: 220
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Post by keithcourage on May 18, 2023 10:48:49 GMT
Glad it's working. One thing you should do if you already haven't is re-grease the CD lens rails. This helps a lot with audio skipping for games with audio tracks near the end of the disc.
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