DD Z1a damaged

[Perry Babin]

There should be no DC on pin 1. It's connected to the audio ground via a resistor. It's a 10k (R10) on the 2-21844 board. It may be the same on this one.

 

[Achim1409]

iam just checking your tutorial for the dwm3640. According to this, Pin 1 should go over 10k to LM211 Pin 2. If i measure From Pin1 to A-Gnd (16) i have 6,2kOhm

 

[Perry Babin]

My fault. I'm swamped with work right now and shouldn't be trying to do tech support when I don't have to do so properly. The 10k and R10 should have made you question it right away.

Pin 3

 

[Achim1409]

Ok, from Pin3 to A-Grnd i have 10k...
How that 074 should work. If i have on Pin 2 and 3 no DC or signal, on Pin 1 should also nothing. If i have a difference between pin 2 and 3, the difference will be on pin 1. Is that correct?
Should on Pin2 and 3 always a little dc to reduce noise?

I cant find, where the A-Grnd should connect to the preamp. Maybe there is the problem.

 

[Perry Babin]

I just realized. That op-amp is supplied with no more than ±5v. Where is the 8-10v coming from?

 

[Achim1409]

other question, from where the 5 v should come? I have only KA78T12 for 12V, and 7815ct and 7915ct

 

[Achim1409]

ok, found this small regulators. There are still ok and producing 5V. Tomorow i will check why there is 10V on the supply of that op amp.

 

[Achim1409]

Ok i had to check otherwise i cant sleep. +5V from the regulator is reaching v+ from that op amp. If i measure from - of that amp i got 10v. From where i got - for that op amp. In my diagramm there is no ground . Only 5+,-5,+15, A-grnd, a-in

 

[Achim1409]

As i can see, A-Grnd is the connection between -5 and +5 V. I got that Voltages on the drive board. If i measure from The OP Amp V+ to A-Grnd i have my 5V. If i measure from V- OP-Amp to +5v i got 10V. How is that possible?

 

[Achim1409]

Checked a little bit today.Negativ from that op amp is connected to cap. C6 and C9. These are parallel to negativ and positiv from that opamp. From C9 is connection to Q3. I think is an A2 but not sure. According measurment it seems ok. Any suggestions?
Also there is a direct connection to Pin 17. -5V.
So if i have +5 and -5 there must be 10V...
Did i made a mistake?

 

[Perry Babin]

V- Do you mean negative rail?

Q3 is likely marked 2A. MMBT3906

For anything before the emitter of Q1 and Q3, you use the audio or secondary ground. For anything from the collector of Q7 and Q9 to the 21844, you use the negative rail for most voltage measurements.

 

[Achim1409]

I dont understand that circuit. On Pin 8 of opamp i have +5V from the regulator. To Pin 4 of that opamp i have-5V from the other regulator. That is all correct. Between this both Pins i measure 10V. That is also correct. How the Voltage should drop to 5V if i have no ground?

 

[Perry Babin]

Please rephrase:
How the Voltage should drop to 5V if i have no ground?

The circuit for the 2-21844 is shown on the class D type 3 page. They are very similar.

 

[Achim1409]

yes, i have that picture in front of me. You said, that this op amp should only have 5V.
Now i have -5 and +5. The difference is 10V.
If i measure between A-Grnd and +5V , than i have +5V.
If i measure between A-Grnd and -5V, than i have -5V.
So normaly it makes more sense if they connect Pin 4 to A-grnd and Pin 8 to +5V. Then i have my 5V.
I dont understand whats wrong here.

 

[Achim1409]

According to you, that i should have only 5V, then somewhere the A-Grnd is missing.

 

[Perry Babin]

Only 5v where?

 

[Achim1409]

your post 125.
On the op amp should only +-5V. From where the 10V are coming...

 

[Perry Babin]

I think you were using the wrong ground reference. The 8v on pin 3 was a problem. If you use the audio ground, is it at 0v?

 

[Achim1409]

ok, i have to check. I used ground from the shunt.

 

[Perry Babin]

Those shunt resistors are on the negative rail. On low voltage, they are only about 20v below ground. Normally, they would be about 100v below ground.