Amp keeps going into protection mode

[Rick79]

O.K.
Please mark that point on the "dial".

Now open D10 (cut it like you did for D8).
With both D8 and D10 open,does the amp go into protection?If it does, at what point?

Measure with the DMM in "diode mode test" D8,D10 and invert polarity, what do we get?

O.K.
Please mark that point on the "dial".

Now open D10 (cut it like you did for D8).
With both D8 and D10 open,does the amp go into protection?If it does, at what point?

Measure with the DMM in "diode mode test" D8,D10 and invert polarity, what do we get?

 

[Rick79]

OK I cut D10 so both D10 & D8 are disconnected. Amp goes into protection at the same point like it was when just D8 was cut.
D8 reads .612 ohms & nothing flipped
D10 ohms .616 ohms & nothing flipped

 

[dorke]

O.K ,
Now cut D9 .
With all 3 diodes D8-D10 cut .Does the amp go into protection?If so at what point?
Measure D9 as you did for D8 and D10,what do we get?

 

[Rick79]

O.K ,
Now cut D9 .
With all 3 diodes D8-D10 cut .Does the amp go into protection?If so at what point?
Measure D9 as you did for D8 and D10,what do we get?

OK with D8, D9 & D10 disconnected, the amp doesn't go into protection at all, I can turn the volume up real high.
D9 reads .618 and nothing flipped.

 

[dorke]

Now cut D11 and measure it.

 

[Rick79]

Now cut D11 and measure it.

OK I did, amp doesn't go in protection and D11 reads .620 and nothing whith probes flipped

 

[dorke]

All diodes measure fine(about 0.6 and flipped Infinity).
Please measure R2 ,R3,and R8 (in circuit) and flip the probes.

What kind of capacitors have you bought?
They should be low ESR and I guess audio grade as well.
Could you please show a photo of the "old and new" ones.

 

[Rick79]

All diodes measure fine(about 0.6 and flipped Infinity).
Please measure R2 ,R3,and R8 (in circuit) and flip the probes.

What kind of capacitors have you bought?
They should be low ESR and I guess audio grade as well.
Could you please show a photo of the "old and new" ones.

Check R2 R3 & R8 in Diode mode? Amp off?

The pair in one photo are the old capacitors. The single ones in the other photos are the new ones.

 

[dorke]

Check R2 R3 & R8 in Diode mode? Amp off?
In diode mode and in ohm mode

 

[Rick79]

Check R2 R3 & R8 in Diode mode? Amp off?
In diode mode and in ohm mode

In Diode mode...
R2 nothing & nothing flipped
R3 .085 & nothing flipped
R8 1.439 & nothing flipped

In Ohms Mode...
R2 9.81
R3 97.1
R8 46.3

 

[dorke]

R3 reading of 0.085 is too low, that makes Q2 a suspect.
Can you please confirm that reading?
If it confirms ,then de-solder Q2 ,take it out and measure it in Diode Mode.
Note Q2 connections on the board before you take it out.
Check between B-E and B-C and C-E and flip (a total of 6 measurements).

on the capacitors:
The Capacitors you bought are from Marcon ,a good Japanese company(if genuine).
But,the date code is very old 1992 ...
In fact, that company was bought by another firm somewhere in the mid 90's.
Is there any way you can check capacitance and ESR somehow elsewhere?

 

[Rick79]

R3 reading of 0.085 is too low, that makes Q2 a suspect.
Can you please confirm that reading?
If it confirms ,then de-solder Q2 ,take it out and measure it in Diode Mode.
Note Q2 connections on the board before you take it out.
Check between B-E and B-C and C-E and flip (a total of 6 measurements).

on the capacitors:
The Capacitors you bought are from Marcon ,a good Japanese company(if genuine).
But,the date code is very old 1992 ...
In fact, that company was bought by another firm somewhere in the mid 90's.
Is there any way you can check capacitance and ESR somehow elsewhere?

Sorry, that zero was supposed to be a six
R3 reads .685
No, I have no other way of testing capacitors.

 

[dorke]

O.K
We shall re-solder the diode gradually,and test while we do that.

We now have all diodes cut ,correct?

Let's Start with re-soldering D9,going into protection?
If so, at what level?

 

[Rick79]

R3 reading of 0.085 is too low, that makes Q2 a suspect.
Can you please confirm that reading?
If it confirms ,then de-solder Q2 ,take it out and measure it in Diode Mode.
Note Q2 connections on the board before you take it out.
Check between B-E and B-C and C-E and flip (a total of 6 measurements).

on the capacitors:
The Capacitors you bought are from Marcon ,a good Japanese company(if genuine).
But,the date code is very old 1992 ...
In fact, that company was bought by another firm somewhere in the mid 90's.
Is there any way you can check capacitance and ESR somehow elsewhere?

O.K
We shall re-solder the diode gradually,and test while we do that.

We now have all diodes cut ,correct?

Let's Start with re-soldering D9,going into protection?
If so, at what level?

Yes, they are all still cut.
OK, I just soldered D9 back. The amp doesn't go into protection at all

 

[dorke]

O.k
add D8

 

[Rick79]

O.k
add D8

OK, I added D8. Amp doesn't go into protection mode at all

 

[dorke]

Can you please measure the DC voltage (2V range) on R2 at minimum-volume and max-volume volume.

 

[Rick79]

Can you please measure the DC voltage (2V range) on R2 at minimum-volume and max-volume volume.

.003 minimum
.090 maximum

 

[dorke]

That is fine.
Now add D10.
protection?

 

[Rick79]

That is fine.
Now add D10.
protection?

OK, I added D10. Amp Goes into protection