5 silver pots on the Turbo Duo pcb?

[kattare]

I just got in an actual US Duo over the weekend.  I'll spend some time with that and a working PC Engine Duo to see what I can figure out.

That duo I was working on last week that wouldn't read the Golden Axe CD ... it's proving difficult.  I did a full cap replace and it still wouldn't read the Golden Axe disk.  The audio got a lot crisper, and it reads CD-R's a lot better now, but it's the only system I have now (out of 4 in my shop) that absolutely refuses to read Golden Axe.  It plays the intro, but when you push start to skip to the title screen it bumps you back to the SCD bios.  (is bios even the word for it?)  Go figure.

Charlie, I'll definitely post numbers on the pots and testpoints here in the coming week or two.  I need to do it anyway so I have a point of reference for future repairs.  I am a little concerned that there will be somewhat significant play in some of them.  I know for instance that while a laser swap should be just a swap, on at least two occasions I've had to go to the pots to get a new laser to read everything properly.  Maybe I'll setup a chart of "before I played with it", and "after I've played with it" on a few different models.  Could be really handy.

[Charlie]

Definitely.  The best thing would be to check each unit and then make a chart of comparison voltages for each measurement point.  This would (hopefully) get us min and max voltages for each one.  (Or, of course, everybody with a working system could tear it apart and screw with the pots until it stops working, then we'd know what the wrong voltages are!)   Seriously, even the various measurements for two or three systems may be enough of a guideline to give a starting-point of the pot settings for future repairs.  And, if you have a unit open anyway, once you get it working, change the pots slightly in each direction until it fails; this will also give a useable min-to-max limit.  The best and final pot setting should, theoretically, be the middle of these two values.

Looking forward to your (and everyone elses') numbers.

Charlie


 

[kattare]

I spent some time tracking down those test points this evening.  Yikes.  The IC101 ones are on the underside of the board.

Forgive my lack of industry know-how here... When taking a reading, I'm guessing we're looking for the voltage between ground and the test point?  I think it's gonna be a bitch to get readings off those pins while the unit is in operation.  Probably have to solder on some test wires or something, then lay the board back down?

I'm wondering if it would make more sense (and be easier) if we were to put together a set of ranges of the resistance of the pots, charted with mins and maxes as you had mentioned.  Trying to KISS on this as much as possible.  The problem I then run into is... between which of the three pins on each pot should I track the resistances?  If I understand the POTS correctly, the resistances between pins A and B can vary, and the resistance between B and C vary inverse to A+B, but the resistance between A and C is fixed, correct?  Thus with just the resistance between A and B, the POT can be adjusted as needed?

[Charlie]

Generally, yes, but see third paragraph below:

I had indicated the measurement points (I hesitate to call them "test points", they do not actually indicate the significant location in the circuit that would normally be monitored for the desired setting) simply to prevent the confusion you mention.  Rather than go into a long explanation, or say something like "first pin on the right when the unit is upside down with ICXX closest to you", or some other garbage like that, I figured it was easier to indicated a single specific un-ambiguous place.  SO...

The best way is to measure the voltage, compared to ground, as I had indicated.  The next best way to is measure the voltage on the pot, compared to ground.  Both of these obviously require the unit to be powered.
The third way, which does not require power, is to measure the resistance of the pot across the pins of the pot itself.   That will probably force the originally unwanted long explanation again.  More significantly, setting pots by resistance does not allow for circuit tolerances, so you will probably still have to go back and tweak those settings anyway.  However, it would be a place to start, and definitely be a help in that the unit would (presumably) "almost work". 

Given that method three may be the most convenient, I'd suggest that the description/explanation include a preface that explains how to access those pots, including the orientation of the board (maybe pictures?).  You may also want to actually indicate the pot values on BOTH sides of the center pin.  This may help in the case where an attempted repair may have damaged the pot; if both sides of the pot read correctly, it is probably ok.  Remember that as one side goes up, the other goes down, and vice-versa.

Charlie

[kattare]

I spent some time this afternoon tracing the pins off the IC on the bottom of the board, looking for test points on the top of the board.  Pretty straightforward actually, there's a pattern to most of 'em, as you'll see.  ;-)

  A
  |
-----
|VR |
-----
|    |
B    C

VR101 = E/F balance, pin 13 of U101  (top side - A on VR101)
VR102 = Focus Offset, pin 18 of U101 (top side - A on VR102)
VR103 = Track Gain (Track error level), pin 45 of U102 (top side - A on VR103)
VR104 = Focus Gain, pin 48 of U102 (top side - A on VR104)
VR105 = VCO, pin 30 of U102 (this one you have to take right off the IC or off the pass-thru close by, as it goes thru a resistor on the under side before hitting A on VR105)

[Charlie]

You are correct, the center tap on a pot is almost universally the middle pin of three-in-a-row, or the single pin separate from the two-in-a-row.

Correct again, the center tap goes directly to those IC pins, except for the one that has the resistor. 

As long as the pictoral/position-explanation, however minimum it may be, is satisfactory, the pot positions should not be too hard to set.  (I just figured that the IC pins was a reasonably un-ambiguous point to find.)  Now that you have the console open/apart, get us the measurements!  Inquiring minds want to know!

And darn it, somebody better be organizing this data!

Charlie
 

[override]

Ok, Here's my bit of information that I have gathered from messing with the pots! I recently bought a laser from pcenginefan willis on teh boards. I recieved the laser and upon installing it was making a high pitched ringing noise such as a bad laser would make. It also would not read CD-R's at all. Feeding from one of my recent unfinished repair post's  kattare added to it with one of his experiences with a laser replacement.

I sent him a PM asking about if he had whinning or ringin noises from his as I am having from mine and also that mine aswell will not read CD-R's.... He responded back with some usefull info on where to start but could not quite remember which pots he messed with....I finally messed with the Duo (Bludgeons) that had the laser replaced and would like to post what findings I have! I started out with a burned cd Ys IV with english patch applied.

The VR102 and VR104 were the culprits in this little deal...The VR102 allowed me to get the high pitched ringing noise to more of the kind of winding noise that you would generally hear. I marked both with a sharpie and started turning, for me it was 1/4 of a turn counter-clockwise to get it sounding correct.

The VR104 on the other hand was 1/4 of a turn clockwise to get it reading CD-R's! I now have perfect results from my brand new Hop-M3 laser, it will read both original and CD-R's flawlessly (I attempted several) with no known errors. It also eliminated the freaking annoying as hell ringing noise that was being produced. Im guessing the focus offset for these lasers is a little to high so it needs to be turned down or vica versa, Im not a master on lasers so I couldn't say for sure. I am also assuming the gain had to be turned up to get the CD-R's to read correctly.

Also I would like to add this bit of information, which was taken by Chop5 when he had soviets board in hand, which I now currently have.

I believe these were the ohm readings the pots gave at stock settings. Chop feel free to correct me if Im posting these incorrect.

VR101 -7.29, 12.59
VR102 -8.10, 7.78
VR103 -13.19, 4.61
VR104 -13.15, 12.58
VR105 -1, 0.43

I would take the new readings at the settings I had for the new laser installed but I dont own a digital meter....Sucks I know 

Hope this bit of information helps others!

[kattare]

Kudos to override for getting that puppy going!


Here's what I have for test values on the pots so far: (I don think xls files are allowed here on the boards, external link to my personal hosting site.)

http://burnside.kattare.com/files/DUO-Test-Values.xls

As you can see, I have a long way to go before I have my desired 3 PCE Duo's and 3 US Duos.  But... i'm getting there.

[dudule]

up:
heeeeellooooo,
thank you for this information, i have taken some measurements;
i've 2 japanaise DUO work perfectly, 1 dead and one in repair, one R an RX she's work perfectly, and 2 SCD².
I would post my results in the future.
Kattare, can i use your DUO test values and repost here ?

I will ask for helps at the French community from Necstasy.

++

edit:
can you tell us what is exactly :

E/F balance
Focus Offset
Track Gain (Track error level)
Focus Gain
VCO

[Vamperica]

i have a duo rx i recently replaced the eye and i think the stuff you have discussed is my problem but i have no idea what pots are and such  i do see 4 dials that you can kinda turn and they ahve the labels you guys have posted but theres no 104 one that i can see.

[dudule]

DuoRX have not vr104.

my DuoRX:
vr101:AB=12.33 AC=10.65 BC=19.55
vr102:AB=7.89 AC=8.11 BC=11.28
vr103:AB=7.25 AC=7.14 BC=18.46
vr105:AB=0.38 AC=0.00 BC=0.38