Derek92994's 700 Ser II White Oak conversion

[laatsch55]

Why are pin three's of the Backplane Boards not connected to Pin three's of the Control Board?

1st gen backplane board...

 

[Gepetto]

Why are pin three's of the Backplane Boards not connected to Pin three's of the Control Board?

It came from here Mark. The PL400 backplane needed this change to support full comp operation properly. This is a 700 but was wired this way.

 

[derek92994]

Quick feed then will get into this, will Re check rail fuses, voltages and follow instructions joe gave.

 

[derek92994]

Cleaned the board....

 

[derek92994]

Pic Without Flash of clean board

 

[derek92994]

Can I clean the side of the board with the components on it with 98% alcohol without hurting the components themselves?

 

[laatsch55]

Yes...

 

[derek92994]

D80 Zener Lifted

Same Results:

VR1:
C 20.2 Volts, Sometimes 7.6, Sometimes 7.6 Then 20.2 for a short time after power down.
A 0 Volts
R 2.5 Volts
VR2:
C 0 Volts
A -20.5 Volts
R -17.0 Volts

I Will now clean the side of the board with the components on it.

 

[Gepetto]

D80 Zener Lifted

Same Results:

VR1:
C 20.2 Volts, Sometimes 7.6, Sometimes 7.6 Then 20.2 for a short time after power down.
A 0 Volts
R 2.5 Volts
VR2:
C 0 Volts
A -20.5 Volts
R -17.0 Volts

I Will now clean the side of the board with the components on it.

You have removed D80 as a potential culprit. Since it regulates properly some of the time and flakey the other times the focus now turns to:
Is R85 intact (not cracked, burned, etc.)?
Does R85 have a solid 100V on one side when you are getting the 7.6V output or is it also dropping?
Does the collector of Q1, the MJE15032 have a solid 100V on it?

If all those things check out, the focus narrows to a flakey VR1.

 

[derek92994]

The R85 is slightly darker than R80 (Pics are before/after cleaning)

R85:

R80:

 

[derek92994]

will do the voltage tests....

 

[derek92994]

You have removed D80 as a potential culprit. Since it regulates properly some of the time and flakey the other times the focus now turns to:
Is R85 intact (not cracked, burned, etc.)?
Does R85 have a solid 100V on one side when you are getting the 7.6V output or is it also dropping?
Does the collector of Q1, the MJE15032 have a solid 100V on it?

If all those things check out, the focus narrows to a flakey VR1.

0.75 Volts on top end of R85, and for some strange reason 0 volts on the C Pin of VR1

 

[Gepetto]

0.75 Volts on top end of R85, and for some strange reason 0 volts on the C Pin of VR1

blown pico fuse?

 

[derek92994]

blown pico fuse?

Lee got me to test the picos on the backplanes, where are the picos on the control board please?

 

[derek92994]

Those Tests I did with VR1 C Pin and R85 were with zener diode lifted

 

[Gepetto]

The pico fuses are on the backplane. With your probing around could you have accidentally blown he positive rail pico fuse?

you are probing in a sensitive area

 

[mlucitt]

It came from here Mark. The PL400 backplane needed this change to support full comp operation properly. This is a 700 but was wired this way.

Got it. (Thanks Lee) I could not see the Backplane Rev version in the picture.

 

[laatsch55]

Got it. (Thanks Lee) I could not see the Backplane Rev version in the picture.

I had been blowing q7 on the pig regularly, this was in response to that..q7 went after other components of course...

 

[derek92994]

The pico fuses are on the backplane. With your probing around could you have accidentally blown he positive rail pico fuse?

you are probing in a sensitive area

I doubt it, I have a good eye and was very steady at the time. I noticed changes after resoldering the back of the board, mainly the left meter pegging, but now its both meters pegging and staying that way on power up. (Edit) "After" I cleaned the component side of the board thats when I noticed C Pin on VR1 was dead. I will re test the picos, ohms I think? And report back after breakfast.

 

[derek92994]

Before I started filming, was testing the left hand side top left pico, without any power to the amp, and my ohm meter just kept going higher and higher (wtf?) very strange.

I have filmed the pico tests separately, and have shown as much as possible in terms of meter range/connections, power up/down etc. I'm an electronics novice so I have no idea wtf is going on with this beauty.