HELP!!!.... Blown Electric Mistress

[bettsaj]

UPDATE:

I've replaced the blown transistor, and plugged it all in and tested. When I switch the effect on I get the usual volume drop as you normally get with these pedals but no effect at all..... I have signal through the circuit though obviously so I'm now concerned that the SAD1024 might be dead.

So far I have replaced:

IC LM741
C9 - 100uf
C10 - 10uf
C11 - 10uf
c12 - 33uf
BC309 (this was replaced with a BC212L as per the original transistor)

Any ideas?

[Scruffie]

Post ya voltages.

[bettsaj]

On all IC's and transistors, or just specific ones?

[bettsaj]

Post ya voltages.

Here you go:

SAD1024 socket (Chip removed)
1 - 0
2 - 3.38
3 - 4.27
4 - 0
5 - 8.57
6 - 0
7 - 8.54
8 - 4.26
9 - 8.56
10 - 4.27
11 - 8.56
12 - 0
13 - 0
14 - 4.23
15 - 3.38
16 - 0

SAD1024 (Chip in socket)
as above except
6 - 2.85
12 - 2.77

IC1 4558
1 -2.93
2 - 3.01
3 - 2.70
4 - 0
5 - 2.73
6 - 3.08
7 - 3.08
8 - 7.86

IC5 LM741
1 - 0
2 - 11.35
3 - 3.85
4 - 0
5 - 0
6 - 3.29
7 - 2.40
8 - 0

IC4 LM339
1 - 5.82
2 - cycles from ~0.60 - 7.51
3 - 8.21
4 - 4.22
5 - 4.19
6 - 1.26
7 - 0
8 - 0.05
9 - 4.95
10 - cycles from ~0.55 - 7.55
11 - 0.27
12 - 0
13 - 0
14 - cycles from ~0.20 - 1.30

[DrAlx]

You're not getting 12V out of your regulator circuit and there seems to be a mismatch in some of the supply voltages read at the pins. Look at

http://www.metzgerralf.de/elekt/stomp/mistress/images/1976-electric-mistress-v2-schematic.gif

and you see several ICs have pins at V+ but you are reporting different V+ values on different ICs and some differ by half a volt.

The BBD can run by on 9V but I don't know if the bias voltage you have reported (3.38) is appropriate for that. Maybe someone with a 9V mistress can comment.

[DrAlx]

According to schematic your 741 voltages don't make sense.
Zener diode is 6.8V but you report 11.35 at pin2 which is way off, and how is pin 7 on that chip at lower voltage than pin 2?

[bettsaj]

According to schematic your 741 voltages don't make sense.
Zener diode is 6.8V but you report 11.35 at pin2 which is way off, and how is pin 7 on that chip at lower voltage than pin 2?

Let me re-measure the pins on LM741... As a matter of interest the voltage on the BC309 collector is 8.2v, where it should be 12.0 to 13.5v

[bettsaj]

The 741 was replaced with a new one..... could be a dud??

Also i had to desolder the old 741 from the board, and solder in a socket for the new chip.... i'll recheck my soldering etc. also.

Anyhoo.... the voltages on LM741 are:

1 - 0
2 - 10.52
3 - 4.38
4 - 0
5 - 0
6 - 3.13
7 - 24.1 (just checked my power supply and that is supplying 24.1v instead of 18v. In my initial readings looks like I put the decimal point in the wrong place... my bad)
8 - 0

[DrAlx]

Looking at the 741 area of the schematic.

"V+" is the output voltage on the BC309 collector.
There is a voltage divider made up of 22k and (33k || 100k), which is basically 22k on top and 23k on the bottom.
So pin3 should measure ( (22/45) * V+ )  and your measurement at pin3 is consistent with your "V+" meaurement even though V+ is far 12V.
So despite some bad voltages, pins 3,4,7 and V+  at least look consistent with each other.

If regulator circuit was working OK, V+ would be about 13V and pin3 would be (22/45*13V) = 6.35V (i.e. close to spec'd zener voltage, which is the desired voltage at pin 2).
So pins 2 and 6 don't look right.  Pin 2 is way higher than zener voltage.
Since your pin2 voltage is much higher than your pin3, the 741 output pin should be driven low but it is far from that (over 3V)

If you have a socket you could try another 741, or you just run jumpers from the socket to any other off-board opamp. 

Did you run the pedal off 24V supply before it broke, and do you get the same problem running on 2x9V batteries?

[bettsaj]

repaired... transistor 121L was in the wrong way around 

Sounds lush