EH Deluxe Electric Mistress SAD1024 question

[newperson]

Hi,
I am messing around with a non effect putting out one of these.  It is the older wide body with internal power transformer.

I think the 1024 is bad, but I would like to double check.

My question is should I get signal out of the sad1024 if there is input signal? Pins 2 and 15 both have input signal and 5,6,11,12 have nothing out.  Could another IC be bad and cause the lack of signal output? 

It has a cd4013, lm311, ua741, lm324, and 4885.  It goes through the 741 and 4558 before the input of the 1024.  I am not really educated on the cd clock and 324 op amp and 311 comparator.




the 1024 pinout can be found here:
http://www.geofex.com/

and the schematic here:
http://www.generalguitargadgets.com/diagrams/dmistsc.gif

[Mark Hammer]

There are three broad classes of reasons why the SAD1024 could still be good and yet you're nopt hearing anything:

1) The BBD is not biased correctly.  BBDs need to receive audio sitting atop a DC bias voltage.  If the bias is off, they don't pass audio.

2) Something may be amiss with the trimpot that sets the output level of the BBD, shunting signal to ground.

3) The BBD is simply not being clocked, so the "brigade" stops at the first bucket.  Here, the 4013 is your likeliest culprit, since the entire circuit runs off 15vdc.  And while CMOS chips like the 4013 will run just fine (and are spec'd for) 15vdc, once things get much above that they are not guaranteed to last.

[Govmnt_Lacky]

Do you have an oscope?

Check for the clock input on SAD pins 3, 8, 10, and 14. That can rule out a bad 4013 chip or its connection to the SAD BBD.

[Thomeeque]

Do you have an oscope?

Check for the clock input on SAD pins 3, 8, 10, and 14. That can rule out a bad 4013 chip or its connection to the SAD BBD.

If you don't have an oscope, simply measure* DC (!) voltage at these pins, you should get cca 7.5V (VCC/2). If you will see 0 or 15V there, clock circuitry is somehow defective.. Give us then DC voltages at all pins of 311 and 4013 chips for further analysis.. T.

* Set it to FILTER-MATRIX mode and adjust maximal RANGE first.

[newperson]

Helllo all,
Thanks for the replies.

I went ahead and put in a new 311 and 4013 just to see.  No change to the effect working.

Here are the readings:

sad1024

1 ground = 0vdc
2 in a = 4.4vdc
3 ck 2a = 7.4vdc
4 nc = 0vdc
5 out a = 14.2vdc
6 out a' = 7.8vdc
7 vdd = 14.2vdc
8 ck1a = 7.4vdc
9 vbb = 14.2vdc
10 ck 1b = 7.4vdc
11 out b' = 14.2vdc
12 out b 7.9vdc
13 nc = 0
14 ck 2b = 7.4vdc
15 in b = 4.4vdc
16 nc = 0


cd4013

1 q1 = 7.4vdc
2 q1' = 7.4vdc
3 clock 1 = 14.3vdc
4 reset 1 = 0vdc
5 d1 = 7.4vdc
6 set1 = -0vdc
7 vss = -0vdc
8 set 2 = -0vdc
9 d2 = -0vdc
10 reset 2 = -0vdc
11 clock 2 = -0vdc
12 q2' = 14.8vdc
13 q2 = -0vdc
14 vdd = 14.8vdc

lm311

1 ground = 0vdc
2 in + = 3.4vdc
3 in - = 2.4vdc
4 vcc = 0vdc
5 balance = 14.8vdc
6 balance/strobe = 14.8vdc
7 output = 14.3vdc
8 vcc = 14.8vdc


How do you check what the bias should be?  And the other information mark posted?  Or do these readings suggest the 1024 is dead?

Thanks again,



From mark:
1) The BBD is not biased correctly.  BBDs need to receive audio sitting atop a DC bias voltage.  If the bias is off, they don't pass audio.



2) Something may be amiss with the trimpot that sets the output level of the BBD, shunting signal to ground.

3) The BBD is simply not being clocked, so the "brigade" stops at the first bucket.  Here, the 4013 is your likeliest culprit, since the entire circuit runs off 15vdc.  And while CMOS chips like the 4013 will run just fine (and are spec'd for) 15vdc, once things get much above that they are not guaranteed to last.

[Thomeeque]

sad1024

1 ground = 0vdc
2 in a = 4.4vdc
3 ck 2a = 7.4vdc
4 nc = 0vdc
5 out a = 14.2vdc
6 out a' = 7.8vdc
7 vdd = 14.2vdc
8 ck1a = 7.4vdc
9 vbb = 14.2vdc
10 ck 1b = 7.4vdc
11 out b' = 14.2vdc
12 out b 7.9vdc
13 nc = 0
14 ck 2b = 7.4vdc
15 in b = 4.4vdc
16 nc = 0

Clock seems alright, maaaybe inputs (2 in a/15 in b) are missbiased, datasheet says that typical optimal input bias is +6V for 15V clock, you may try it..

Good luck, T.

[newperson]

No change withe the bias adjustment.

Do you think at this point you would agree with the conclusion the 1024 is dead?

Thanks again,

[newperson]

I would like that thank everyone for suggestions on this repair.  I found the problems and would like to report them in case it might help someone else.

The 324 IC was partly bad and needed to be replaced.
R15 47K resistor was bad.  It drifted to 230K.  Replaced.
1024 was bad.

[Govmnt_Lacky]

Wow!! Good job findings those. Especially the resistor. Bad resistors can cause huge headaches for debugging.