Hartke A70 blow the fuse

[Fabrizio]

yes it is -16vdc

[Fabrizio]

This is the voltage I read across the circuit. Using the multimeter with black to the hearth and red to the junction.

[Jazz P Bass]

A few of those are redundant, but better than nothing.

Now move on to the output transistors.
Base & Emitter voltage.

It would also help if you measured the Base & Collector voltages of that lower NPN: it looks like Q4.

[Fabrizio]

Hi jazz bass,

sorry for late reply. These are the readings in Vdc :

Q12 B=-41.6 C=45 E=-42
Q9 B=-42 C=-44.7 E= - 42.6
Q4 E=-44.9 C=-43 B=-44.8

Thanks for helping

[Fabrizio]

Hi Guys, could you help me please? Any suggestion/troubleshooting is welcome

[Fabrizio]

sorry mistake those are the correct readings

Q12 B=-22 C=44,2 E=-42
Q9 B=-42 C=-44.7 E= - 42.6
Q4 E=-44.9 C=-43 B=-44.8

[Jazz P Bass]

That schematic is really hard to read.

The base of Q12 must be a positive voltage.oltaGE

Follow the path.
The B+ rail voltage comes doen through two resistors to the base of Q12.
Is the lower resistor open?
If it is not, then the bias transistor on the heatsink is probably at fault.

[Fabrizio]

Hi Jazz bass,

the schematic is on the top of this thread on a pdf file. Bill52 posted it.
Those resistors 60 and 61 are ok not open or shorted.
For bias Transistor you mean Q6 ?
I did test it before and looked ok
with the diode test. I ordered this by the way and as soon it arrives I will change it to see if is that.

[Jazz P Bass]

Now that I have a schematic that I can read.....

You have more problems than a bias transistor.

Something on the lower rail is shorted.
Q9's Emitter is full on.

[Fabrizio]

Hi jazz Bass,

First I would like to let you know how I measure the Voltage(just in case I am doing something wrong)
I measure the voltage by putting the black(-) on junction J10A on the negatif. and the red on component.

Then I looked at the emitter of Q9 and Resistors are fine(R64,56,55,48 are all ok not shorten) Am I missing something ? What else should I check?? Thanks

[Jazz P Bass]

Have you double checked Q4?
Have you lifted (leave them lifted) one end of D6 & D7?
Check D12 & D13. If they show as shorted but they are not, then Q11/12 and or Q5/9 are shorted.

[Fabrizio]

i did check q4 and it was ok not shorted.
I have lifted one end of D6,D7,D12,D13 and checked with diode test on the multimeter., everything ok.

[Jazz P Bass]

Leave all of those diodes lifted & power it up.

Something is putting votage on Q9's emitter.

[Fabrizio]

Hi Jazz Bass,

I lifted all diodes and power it up .

Now the readings are:
Q12 b= - 43 c= 46,3 e= - 43.5
Q9 b= - 44 c= - 46 e= - 43.5

What do you think?

[Jazz P Bass]

What do I think?

I see - voltage on the base of Q12.
It should be about 0.50 volts positive.

Check Q5 for a short.