Old EHX Electric Mistress not working

[Ed22]

Hi,

this is a non-deluxe version. green letters.
got this unit from a friend. he says one day he plugged a wrong adaptor in it. Since then it does'nt work anymore. I tested it, but there are lots of BUZZZ, i can hear so few my guitar.
I did a test with an audio prob. still the same issue : when i touch the ground track with my prob, there is a terrible BUZZZZZZ. Still i can hear the music i put at the input.
What can i conclude for the moment? current passes through the board, doesn't it?

2 other things :
1)someone tried to fix it. a BC309 has been replaced by a 2N2907. Is it correct?
2)a diode 1N 4007 is soldered directly to the power jack (to plug a wallwart). looking at the schematic, this diode should be a 2N3563. correct replacement too?

thanks for your help,

Ed.

[theehman]

EH had released a power supply modification page back in the 70s which called for replacing the BC309 w/ a different transistor (2N4354) and the 2N3563 with a 1N5235B diode.  Likely the zener and the 741 in the power supply stage are bad.  You should get about 12-13v on the collector of the 2N4354.
The diode i there now is probably just for polarity protection as the 2N3563/1N5235B should be on the board after a 100k resistor and connected to pin 2 of the 741.

[Ed22]

Hi Ron!

thanks for your help.


got 15 V on the collector of 2N2907.


So you suggest to replace the diode, bc309 and 741 in the powersupply section?
what about the other bc309 linked to the LM339N? do i have to change it also (i've seen in the schematic that it is referenced as 2N5087)?

about the 741 : any type should fit?
maybe i'll change the rc4558. that would'nt do harm...

regards,

Ed.

[theehman]

You should have 12 - 13.5v.  If you've got voltage there I'd bet something else is dead.  I'd audio probe the SAD1024 in/out to isolate the problem. 

The BC309 on the LM311 is fine.

[Ed22]

Hi,

got :

0 on pin 1 (ground)
8,2 on pin 2 (IN A)
8    on pin 3
0    on pin 4
16   on pin 5
10  on pin 6
16  on pin 7
16  on pin 8
16  on pin 9
10  on pin 10
11  on pin 16
10   on pin 12
0    on pin 13
7,9  on pin  14
8,2   on  pin  15
0  on  pin  16

don"t know what to conclude from this.

regards,

Ed.

[Ed22]

oh and i've audio probed each pin of the sad. can't hear anything but a huge BZZZZZ....

Ed.

[theehman]

Something's shot.  Check continuity of the ground on the board to the chassis.  Check the 4558 in/out.

[Ed22]

How do i check continuity of the ground to the chassis?...

thanks,

[theehman]

How do i check continuity of the ground to the chassis?...

thanks,

Use either your continuity setting or the lowest resistance range.  Put one probe on the chassis and one on the board's ground trace to make sure they're still connected.  You should get a reading close to 0 ohms.

[Ed22]

Ron,

here are the voltages at the 4558 and 741:

for the 4558:
1: 8,2V
2: 8,28V
3: 7,35V
4: 0V

for the 741:
1: 0V
2: 6,48V
3: 8V
4: 0V
5: 0V
6: 16V
7: 16V
8: 0V

I haven't test the ground continuity yet...

thanks,

Ed.

[Ed22]

sorry, i missed some while writing:

for the 4558:
1: 8,2V
2: 8,28V
3: 7,35V
4: 0V
5: 7,35V
6: 8,20V
7: 8,1V
8: 16V

my apologies

Ed.

[theehman]

Replace the 741 and the 2N4354 or whatever it is after pin 6 of the 741 and 100k resistor.  Your voltage is passing straight through the transistor.

[Ed22]

Ok, Ron

i'll do it (don't have these parts for the moment) and will keep you up.

thanks very much,

Ed.

[StephenGiles]

You should have 12 - 13.5v.  If you've got voltage there I'd bet something else is dead.  I'd audio probe the SAD1024 in/out to isolate the problem. 

The BC309 on the LM311 is fine.

I'm confused - don't you mean the 339?

[theehman]

You should have 12 - 13.5v.  If you've got voltage there I'd bet something else is dead.  I'd audio probe the SAD1024 in/out to isolate the problem. 

The BC309 on the LM311 is fine.

I'm confused - don't you mean the 339?

Yeah, I was looking at the wrong schematic.

[Ed22]

EH had released a power supply modification page back in the 70s which called for replacing the BC309 w/ a different transistor (2N4354) and the 2N3563 with a 1N5235B diode.  Likely the zener and the 741 in the power supply stage are bad.  You should get about 12-13v on the collector of the 2N4354.
The diode i there now is probably just for polarity protection as the 2N3563/1N5235B should be on the board after a 100k resistor and connected to pin 2 of the 741.

I'm in Europe. can't find either 2N4354 and 1N5235B... tried with Dasmusikding and Banzai effects (i usually get my components from them because i can buy very small quantites with them).
So are there substitutes for these 2 parts?
(or if someone has got these, contact me, please)

thanks very much,

Ed.

[theehman]

2N4354 - same as NTE129

1N5235B - 6.8v, .5w zener

[Ed22]

sorry haven't find either NTE129...

is there something that could do the job here?

http://www.musikding.de/index.php/cat/c60_Transistors.html

sorry for that...

thanks very much,

Ed.