All things G1176 - the new "repost" thread.

[gswan]

I doubt it has anything to do with the GR amp.
You can disable it and still measure a change on the FET gate, and there should be no change on the Anode of either of the FDH333 diodes.

 

[a2d]

on CR3 with the release pot full CW I have a reading of -1.493 and on CR4 -1.501
and with the release pot  full CCW on CR3 -.880 and on CR4 -.876

 

[Chrome Heart]

It all started with Q1 and Q10 in the right/ wrong way, I didn't know that they are not the same as the screaning
I've had every component in the GR meter driver amp and GR control amp out and tested and reinstalled,
I even replaced all the BC107's I going to switch out Q6,Q7,Q8,Q9 and see what happens

Yes. Q1 and Q10 could be in the wrong way (if you orient them according to the print on the PCB)  using the 2N5457 FETS  as opposed to the BF245A because the pins are reversed. I dont know if that would damage them or not. Did you replace them?

 

[gswan]

on CR3 with the release pot full CW I have a reading of -1.493 and on CR4 -1.501
and with the release pot  full CCW on CR3 -.880 and on CR4 -.876

This is on the Anode or Cathode of these diodes?

 

[a2d]

yes I did have them in the wrong way in the beginning, I did replace them, I got a good matched set from HB

It all started with Q1 and Q10 in the right/ wrong way, I didn't know that they are not the same as the screaning
I've had every component in the GR meter driver amp and GR control amp out and tested and reinstalled,
I even replaced all the BC107's I going to switch out Q6,Q7,Q8,Q9 and see what happens

Yes. Q1 and Q10 could be in the wrong way (if you orient them according to the print on the PCB)  using the 2N5457 FETS  as opposed to the BF245A because the pins are reversed. I dont know if that would damage them or not. Did you replace them?

 

[a2d]

ummmm the side with the stripe lol

on CR3 with the release pot full CW I have a reading of -1.493 and on CR4 -1.501
and with the release pot  full CCW on CR3 -.880 and on CR4 -.876

This is on the Anode or Cathode of these diodes?

 

[gswan]

Great. That's what I thought. That would be point 19.
Can you measure the following:
-10V rail.
Voltage across R83.
Voltage on wiper of Qbias (ie point 18) at each extreme of the Qbias pot.

 

[a2d]

Great. That's what I thought. That would be point 19.
Can you measure the following:
-10V rail.
Voltage across R83.
Voltage on wiper of Qbias (ie point 18) at each extreme of the Qbias pot.

as for the voltage across R83 do you mean measure each side to grnd or probe  each side of the resistor

Gswan I'm very greatfull for your help!!!

 

[gswan]

One side of R83 should already be attached to GND, so the voltage across it will be WRT GND unless it is floating.

 

[a2d]

ok I'll check

 

[a2d]

ok my negitive 10v rail is -9.85v
across R83 1.945v
voltage on bias full R -2.918 full L 0.6mV

Great. That's what I thought. That would be point 19.
Can you measure the following:
-10V rail.
Voltage across R83.
Voltage on wiper of Qbias (ie point 18) at each extreme of the Qbias pot.

 

[gswan]

ok my negitive 10v rail is -9.85v
across R83 1.945v
voltage on bias full R -2.918 full L 0.6mV

Something wrong here.
-V rail looks OK.
The voltage across R83 should be the same as the voltage when the Qbias pot is fully R (in your case).
Check that the pot is correctly installed, there are some jumper/links for certain types of pots I think. What type did you use? Check that the pot is correctly in circuit and connected to the junction of R83 and R82.

 

[a2d]

yes its the same -2.85v across R83 and bias fully Rt and pad 18 I think I made a typo last post sorry

 

[a2d]

on pad 18 there is -2.913v with bias CW and release  CCW with te release CCW there is -2.903v the is good i think

 

[gswan]

on pad 18 there is -2.913v with bias CW and release  CCW with te release CCW there is -2.903v the is good i think

That looks good. The pot is not upsetting the bias at the Qbias trimmer point. It is further up the chain.
Check the values of R7 and R8 as well, just in case.

 

[a2d]

I'm just about to start testing that section of the circut,
I was convinced that the issue was in the GR part but I guess not
R6,7,8 are good

 

[gswan]

First measure the voltage swing when turning the release pot at point (7) and then again with the connection from (7) to the FET disconnected.

 

[a2d]

can I disconect it at the pot?

 

[gswan]

Yes, we want to measure the voltage swing at the intersection of the two pots with the FET circuitry connected and then disconnected to ascertain whichg part of the circuit is causing the disruption.

 

[a2d]

ok release pot full CCW -3.61v and full CW 1.07v