Repair Guide (ish) ... Laser Power Issues? Replace Caps

[kattare]

I got a new pc engine duo from Japan today.  I always get so excited when a new one comes in.  Don't ask me why.  ;-)

In any case, this one came with a copy of Golden Axe, which was 50% of why I picked this particular one out of the many on Ebay at the time.  So I go straight to it, hook it all up, put in Golden Axe and it loads up after a slight delay and goes into the intro.  Yay, I'm stoked.  This is the first time I've seen Golden Axe on the duo.  I got sick of the intro (I don't grok Japanese) and push 'RUN'.  Boom, I'm back at the CD Load screen.  WTF?  A few more tries, and it looks like every time it's about to load the game's title screen, it just craps out and reloads.  So... I'm pissed.  This particular unit was sold as a functional one.  (Partial refund time.)

I lost interest in the unit right away tho, (put it in the fix pile) and took the Golden Axe CD to another duo that I know works.  (I'd played a few CD-R's on it already.)  Holy Crapola, this duo wouldn't even load the intro... so now I'm thinking it's the CD.  Just to be sure I drop it into a "never fails" duo-rx and it loads right up, goes to the title screen as it should, and plays right off.  After playing for about 30 mins...  (You know, cuz I love Golden Axe... and... DAMMIT, this version SUCKS. :-(  I am so bummed.

Right, so after playing about 30 mins my itch comes back to fiddle with the two duo's that wouldn't play it.  So far I've only had time to look at one of them. (The second one, that wouldn't even load the disc at all.)  But here was my procedure to get it working:

1) Inspect board for corroded contacts on the caps.  Several of the larger 22uf ones looked bad so...
2) Replaced out ALL of the larger 22uf caps on the board.  (there seem to be two sizes of the 22 uf ones.)
3) Test unit.  No change.  (dammit.)
4) No more contacts or caps look corroded, so I went with the old standby common failures... the 47uf and 100uf...
5) 47uf first... replaced them all... test unit.  No change.  (dammit.)
6) 100uf... replaced them all... test unit... I'll be damned.  It reads fine, plays fine.  Sweetness.

So here's the thing.  Having been through a few of these now, (4 or 5?) and having fiddled with lasers and their power pot and all the adjustments on the other 5 pots and everything else... I really believe now that the caps failing is one of the most common causes of laser issues.  I think that as the 100uf caps fail the laser must not get enough juice anymore or something.  Tweaking the pot on the laser probably compensates for that somewhat, and may be an easier tweak, but really doesn't address the core issue nor is it a long term fix, as the caps ARE going to fail... sometime.

As to why that duo would read CD-R's and not Golden Axe... who knows... Golden Axe was actually the first game I've thrown at it that it wouldn't play... but now all those caps are swapped out, everything loads faster, it's pretty much on par with my duo-rx.  I'm happy, I've got a new repair procedure that is actually less guessing than it used to be.  Here it is so far... (and yeah, it's gonna evolve...)

- Power Issues?
  1) Clean AC Plugs and Unit Socket with solvent.  (once got a broken duo for $40 and this was ALL IT NEEDED)
  2) Check / Replace Fuse
  3) Check / Replace VR  (part # anyone?)

- Audio Issues?
  1) Reseat / Resolder DIN-5 (I pretty much do this every time... just one of those things that needs to be done because it's under so much stress.)
  2) Replace Audio Related Caps (very well documented elsewhere on this board)
  3) Replace Audio Related IC's.  (never got this far personally...)

- Video Issues?
  1) Reseat / Resolder DIN-5
  2) Try A Different Game.  ;-)

- CD Reading Issues
  1) Clean Lens
  2) Check Spindle Height (sometimes these get knocked down pretty good in shipping.)
    -) (Added 07/09/09) If it's too low, and disc's are grinding on the chassis, you can try putting a spacer of some kind (thin washer?) under the disc.
    -) (Added 07/09/09) If it's too high (> 1mm above the chassis in my experience) you can try GENTLY tapping it down with a small hammer.
  3) Check Spindle Balance (if the disk spins 'wobbly' the unit won't read it on the outside tracks.) (UPDATED 07/09/09)
    -) You can find the high point in the wobble by snagging a disc you don't care about...
    -) and a sharpie or pencil and holding it above the disc while the disc spins...
    -) slowly lower it until it leaves some marks... now you know where you need to GENTLY bend the platform down to try to achieve balance.
  4) Swap Laser (I have several on hand that are known good, so this is an easy elimination step.)
  5) Replace 100 uf, 47 uf, and the larger 22uf caps, in that order.
  6) Adjust the 6 pots.  (UPDATED 07/09/09)
    -) For me at this stage this is just a very careful guess and check.  Mark their original positions BEFORE YOU TOUCH THEM!
    -) There are 5 on the board.
    -) And one on the laser assembly.
      -) Two of the pins connect into the same trace on the board.
      -) Measure across one of those and the third pin.
      -) Readings known to work are 550 ohms to 760 ohms.

  (Added 07/09/09) Note: I now have four disc's I use to test nearly all usage scenarios.  I test in this order:
    A) A music disc.  (paying special attention to the last couple of tracks.)
    B) A regular TurboDuo game... usually Fighting Street for me.
    C) Golden Axe... it's known to not like being read.
    D) A Turbo Duo Demo Disc CD-R.  The intro on this includes a brutal cross-disc seek that kills all but the most finely tuned Duo.

I'm sure some of you are wondering what I'm doing with them after I've got 'em up and running.  I'm sorta ashamed to say, I've been dabbling in Ebay.  On the other hand, I figure my time is worth something -and- I need the cash -and- after leaving my shop every one of these units is worthy of sitting on my own video game rack, so hey, someone's actually getting a good deal.  I'm way jealous of these dudes that get like $500 for their units.  I have no idea how they do it.  I list mine in the $200 - $250 range (depending on what I paid for it and what parts went into it.) and I still only get buyers every here and there.

Anyway, back to the repair guide bit... Anyone have anything to add?

I'll work on the original unit that got me started this evening sooner or later and I'll post a followup to let everyone know if it was the 100uf caps again.  ;-)

[kid_rondeau]

This is excellent. I'm planning to someday make a cap replacement guide for the TG-CD, which no one seems to have done yet.

[Charlie]

As I have mentioned in another post, if you can list the caps you replaced by number, I may be able to tell what their function is.  This data would then be "food" for the hoped-for repair manual. 

If I may suggest, it would be an additional help to measure the voltages at the measurements points (see other post).  This would help others who may need to adjust the pots; there would be less trian-and-error.

Thanks
Charlie

[kid_rondeau]

If I may suggest, it would be an additional help to measure the voltages at the measurements points (see other post).  This would help others who may need to adjust the pots; there would be less trian-and-error.

Charlie, please provide link to your other post....

[Charlie]

"Charlie, please provide link to your other post...."

https://www.pcengine-fx.com/forums/index.php?topic=3586.0

Oh,oh, if it's that hard to find, others may miss it also.  This will make the repair manual more difficult to compose.

Charlie

[kattare]

I've updated my guide a bit...

Also - Follow up on that original unit that was refusing to read Golden Axe.

I took a reading on the pot on the laser assembly, it was higher than I'd seen elsewhere... 830 ohms.  Elsewhere (both personally, and in these forums) I'd never seen a reading higher than 760ish.  So I was gonna tweak the pot, but they're glued and it wouldn't budge.  ...gotta be careful here, I actually broke one of these pots once trying to unstick it...  so instead of forcing it, I put a 10k resistor across the pins.  Resistors in parallel reduce the resistance, but you have to do the proper math to determine the values to use.

That dropped the overall reading to the expected 750 ohms and viola!  It now reads Golden Axe!

[Charlie]

FYI, that pot adjust the drive level on the LED.

Charlie