DD Z1a damaged

[Achim1409]

Pin 1 of IC 203 also good Signal. Pin 2,3,5,6,7 nothing. IC 102 Pin 13 also nothing. So maybe IC203 damaged?

 

[Perry Babin]

Which pin drives the cap that feeds the input to the driver board?

 

[Achim1409]

A little bit confusing, because not everything is marked in the diagramm.
Ok.Signal passing tru C175 (50V,10uf) : minus from that cap is going to Q102m(K30A).
one Pin of K30a is connected to ground, the center pin is going to resistor R105m.
According diagramm it should go to Pin 14 of IC102, but it seems much different. I will recheck.

 

[MrSllez]

It might be possible that you have a bad transformer that shorts when moved?



There is a guy on youtube called "barevids" and he does amplifier repair videos. It might be helpful to watch some or ask him about his opinion. Here is the link if you are interested: YouTube

 

[Achim1409]

Hello, thanks for that video. I will look later. But i think there is something more wrong. Because if i twist and press the transformers, nothing happen. Without rectifiers inside everything is ok. There is no audio at the moment and bad noise.
If somebody may have a diagramm for that pre-amp section for Revision2. I have a diagramm only for newer one.

 

[Achim1409]

ok, i think i found. Its going to pin 13 of IC102. There is a ceramic capacitor wich is parallel with Pin 14.

 

[Perry Babin]

I'm guessing that it's a TL074. Pin 13 is an input to the op-amp. The 4 corner pins are the output pins.

 

[Achim1409]

Yes, TL074L

 

[Achim1409]

on all 3 corners i have a signal. Except on 14, there is only dc

 

[Perry Babin]

What is the DC voltage on pins 12, 13 and 14?

 

[Achim1409]

Pin 12 0V, Pin 13 -4V, Pin 14+ 5V

 

[Achim1409]

Pin 12 0V, 13 -4V 14 +6v

 

[Perry Babin]

Let's disable the output stage. Discharge the rail caps and Connect a jumper between the collector and emitter of Q10 on the driver board.

Does that change the voltage on that op-amp?

 

[Achim1409]

Output disabled, still the same voltages.

 

[Perry Babin]

If you do as you would if measuring the voltage on pin 13 or pin 14, if you let the probe short pin 13 to 14, does the voltage go to 0v?

 

[Achim1409]

in that moment when both are shortened, it dropped to 0V

 

[Perry Babin]

Find the op-amp that's driving pin 13 and post the voltage on the 3 terminals for that op-amp.

 

[Achim1409]

IC203 (MC4558) Pin5 0V, Pin6 0V, Pin7 -14V

 

[Achim1409]

On Pin1 ive got a Sinewave. Pin 2 and 3 0VDC and no signal
Ive got on Supply about 30Vdc. On all OP Amps. But Input at that Board is only 15VDC

 

[Achim1409]

I changed that op amp. Now a got this signal on the drive board.
Input is 100Hz Sine with 6Volt.