phase 90 help

[cmat]

Hi guys!  I have a script phase 90 that I just cant debug.  Someone put an adapter jack on it and plugged in a cheap adapter with a polarity switch and had it set wrong so no more phase.  I opened it up and the Zener was burnt it was burnt bad enough that it burnt the board and the traces around it.

The only sound I can hear is a very faint non phased sound and if I hit the strings really hard it sounds gated.

The first thing I did was replace both diodes I just knew this was the problem.  Still nothing
Next I replace the 2n5952 (matched) and the the 4126 nothing.
Next I replaced the 6 single opamps.  741 nothing.
While I was doing it I recaped it

I also found some broken wires which I fixed.

Does any one have any ideas?  I will post voltages but I cant find a schem whith the ICs labled I am sure everyone know which ones are which so I will get voltages and explain where they are on the board if you need them.  I am hoping someone has been in the same situation.  I am stumped!

Any help would be greatly appreciated.  Thanks guys!

[R.G.]

1. Connect your DMM set to resistance to the ground lead of the input jack. Read resistance to pin 4 of the ICs. You should get 0 ohms to all pins 4. Also to the output jack ground.

2. Remove the battery, connect your DMM lead to the + terminal on the battery clip. Read resistance to pin 7 of all the ICs. You should get 0 ohms.

Any problem with 1 or 2 indicates you still have a wiring error. If those dont' help, take a couple of digital photos of the top side of the board and post them. Identify on the photos which wire goes to where on the external wiring. Then number the ICs and transistors however you like.

With that done, measure pin voltages and post them.

It is possible that the traces around the diode that you fixed were not completely fixed.

[cmat]

Thanks for the reply RG!  I checekd for resistance there is none.  I cant find my camera (I think my wife has it)  I will take measurements of the voltages and list it.  Thanks alot!

[mdh]

2. Remove the battery, connect your DMM lead to the + terminal on the battery clip. Read resistance to pin 7 of all the ICs. You should get 0 ohms.

Pin 7?  Don't you mean pin 8?

[cmat]

OK I dont have a pic.  If you are looking at a phase 90 (script with 6ICs) and the trimpot is at the bottom I am going to label the chips on the left side starting at the top will be the below it 2.  On the right the top one will be 5 and 6 below it.  The 2n5952 top 1 below it 2 and so on.  I hope I havent made this confusing
                IC1                                                                                                                                           IC 5
pin 5  .11v      pin4 0v                         D 5.66  S 9.1  G 2.33             4125  E 9.1  B 8.48 C 7.1                      Pin 1 O        Pin8 0
pin 6  4.84v    pin 3 5.68v                                                                                                                        pin 2 4.23    pin 7 4.23                     
pin 7  4.23v    pin 2 5.54                                                                                                                          pin 3 4.21    pin 6 4.21
pin 8  0v         pin 1 1.14                                                                                                                          pin 4 0        pin 5 0
                                                                                                                                                                     IC6
             IC2                                                                                                                                             
pin5  4.86v     pin 4 4.87v                    D 5.61 S 9.1  G 2.19                                                                        Pin 1 .01     pin 8 0
pin 6  4.82      pin3 5.76v                                                                                                                          pin 2 4.19   pin 7 4.22
pin 7  4.2       pin2 5.63                                                                                                                            pin 3  4.25  pin 6  3.75
pin 8  0v        pin 1 4.86v                                                                                                                          pin 4 0       pin 5  0

             IC3
Pin 5 .07        pin 4  0                        D 5.55  S 9.1  G 2.33
Pin 6 4.83      pin 3  5.57
Pin 7 4.23      pin 2  5.48
Pin 8 0          pin 1  .08

            IC4
Pin 5  .06      pin 4 0                          D 5.5   S9.1  G 2.33
pin 6  4.27    pin 3 5.5
pin 7  4.23    pin 2 5.39
pin 8  0         pin 1 .08

Zener 4.21 v    1n914 9.08

Any help would be greatly appreciated.  Thanks!

[mdh]

2. Remove the battery, connect your DMM lead to the + terminal on the battery clip. Read resistance to pin 7 of all the ICs. You should get 0 ohms.

Pin 7?  Don't you mean pin 8?

Oops, my bad, didn't realize these were singles 

[cmat]

Do these voltages look right?

[mdh]

I'll take a crack at it.  Maybe I can redeem myself.  It looks to me like all pins 7 (V+) and IC2 pin 4 (V- = ground in this case) are suspect.  I would expect all pins 7 to be at about 9V (supply voltage), and all pins 4 to be at 0V.  Other than that, the JFET drain and gate voltages look believable, but I think the sources should be closer to the drain voltage.  So the 9.1V readings on all of the sources and the emitter of the 2N4125 are bizarre.  The base and collector voltages on the 2N4125 look weird, too.  I have a working six stage version of this circuit on the breadboard at the moment, and the voltages on that transistor are approximately (E, B, C) 5, 4.5, 2.6.

The other telling fact is that the zener voltage is pretty much the same as the voltage that's showing on pins 7 of all of the ICs.  Furthermore, the voltages on the sources of the JFETs should be strictly equal to the zener voltage (if you look at a schematic for the circuit, you'll see that the sources are tied directly to the zener), but instead they seem to be equal to the supply voltage.  This suggests to me that some of the offboard wiring got screwed up, and somehow Vref and V+ got swapped.  It's hard for me to imagine how that could happen, but I haven't seen how the original pedal is wired, and that's what the voltages seem to be indicating.

[cmat]

OK Thanks alot!  I will check the schematic again and check the wiring.  This thing had so many problems that I could have made a mistake on the wiring.  I will check it right now and let you know.  thanks again!

[cmat]

OK I feel like an idiot.  If I had looked at the schematic instead of assuming that who ever worked on this before me had the + in the right place I would have been alot better off.  They had the + to the trim pot.  Now I have another problem The phase is super weak ,barely audible.  Biasing it doesnt fix it.  Do you think the wiring problem could have fried something?  Should I change the jfets again?

[mdh]

Did you match the FETs before you put them in?  See the FET matching article at GEO if you don't know what I'm talking about: http://geofex.com/article_folders/fetmatch/fetmatch.htm.

[cmat]

Yes they are matched

[mdh]

Hmm... then another round of voltages may be in order.  I suppose it's possible that something's fried.  Maybe start with IC2, since that's the only one where the V- pin was at a greater voltage than V+?  I know reverse voltage can fry op amps, but I don't know if a few hundred millivolts will do it or not.  And I have no idea what effect those voltages might have on the FETs.

[cmat]

OK I replaced IC2 and the jfets and I still have the same problem.  I will take some voltages and repost.  Thanks

[mdh]

Have you verified that turning the trimmer actually changes the voltage on the gate of the FETs?  It's possible that you toasted the trimmer in the process of wiring the supply voltage incorrectly.  I don't know what the odds of this are (pretty good, I think, if V+ was connected to the wiper), but it's been known to happen.  You might check the resistance among the trimmer terminals with power removed from the circuit, turning it a little this way and that, and making sure that the values make sense.

[cmat]

Thanks for the reply.  I can hear a change in the circuit when turning it but I will put a new one in it tommorow.  I am willing to try anything.  This thing has been a nightmare!  If it were mine I would toss it.  It just isnt worth the headache

[cmat]

OK I took some new voltages here they are.  I have phase but you have to listen really hard to hear it it is almost inaudible
       IC1                                IC5
5) 1.49     4) 0                 1) .01      0                                      Q1
6) 8.2      3) 8                  2) 8.15    7) 9.16                        D)  7.97   S)  8.08  G)  8.07 
7) 9.2      2) 8.19             3) 5.78     6) 8.15                                 Q2
0        1)  .01              4)  0         5)  .01                        D)  7.95   S)  8.08  G)  3.05
                                                                                                Q3
      IC2                               IC6                                        D)  7.9     S)  7.99   G)  3.13
5)  7.91   4)  7.91           1)  .01         0                                     Q4
6)  8.13   3)  7.97           2)  7.41     7)  9.16                       D)  7.5     S)  7.75   G)  3.06
7)  9.19   2)  8.13           3)  6.93     6)  7.5
  0       1)  7.9             4)  0          5)  0                                   4125     E)  7.8   B)  7.78  C)  3.84

       IC3
5)  .01      4)  0
6)  8.17    3)  8.07
7)  9.17    2)  8.16
  0        1)  .01

          IC4
5)  .01      4)  0
6)  8.17    3)  8.07
7)  9.17    2)  8.18
  0        1)  .01


Does any one have an idea?  I really appreciate any help.  Thanks!

[mdh]

Goddamn smilies.

Pin 4 of IC2 is wrong, if it really is as you reported... maybe a solder bridge somewhere?  Should be at 0V like all of the other pins 4.  The FET source and PNP emitter voltages also seem wrong.  They should be closer to 4-5V, depending on the zener voltage.  It sounds like the offboard wiring has been messed with a lot, in which case you may need to just sit down with the schematic and the board and trace things out carefully to verify that you haven't missed something.

[cmat]

What is the deal with smileys???  I didnt post them maybe it has something to do with the 8 and the ).  This thing is all screwed up.  I am just going to have to spend alot more time with it.  I hate this thing!  I thought the voltage on IC2 was wrong.  I will work on it some more.  Thanks for the help