While the Output relay is switched on briefly, Pin 26 reads 2V, then reverts to 0V when the Standby lamp comes on

It is getting late here and I am leaving the amp alone for the moment. I hope my information is helpful in identifying possible faults and thank you again to Dodgydave and Peterdeco for their advice so far, and thank you in advance to anyone else out there who may have some guidance I can follow. Good night for the moment

 

Don't turn the volume control up while testing.

For the following test, turn the volume to 0, the lowest setting.
Disconnect all speakers.
Measure the voltage at the following locations with respect to GND.

TP303
TP305
TP304
Tp306

 

Don't turn the volume control up while testing.

For the following test, turn the volume to 0, the lowest setting.
Disconnect all speakers.
Measure the voltage at the following locations with respect to GND.

TP303 = -0.05V
TP305 = 0.05V
TP304 = 4.7V
Tp306 = 4.4V

Ok, I measured the above voltages on the TPs, with the DMM COM lead on GND

 

Ok, I measured the above voltages on the TPs, with the DMM COM lead on GND

...and thank you for your help Mr Chips

 

Thanks for the measurements.
These indicate that the RIGHT channel is out of balance.

Unplug the unit from AC mains.

Here is the layout of ICQ control board.
Are you able to post well focused photos of the top side and bottom side of this board?

I would like you to unsolder one leg of R708 and lift the leg off the board.
(An alternative is to snip one leg of R708 halfway along the leg. This way we can solder the leg later.)

Apply power with no speakers and volume set to 0.

 

MrChips, I've uploaded photos of the board as requested, are these clear enough for you ? I have to go out now and I will take care of R708 a little later and report back. Many thanks

 

MrChips, I've uploaded photos of the board as requested, are these clear enough for you ? I have to go out now and I will take care of R708 a little later and report back. Many thanks

Ok, I desoldered one leg of R708, plugged back into the mains and switched on the amp. It goes through the preheat sequence then the Output red light switches On and stays On. So far so good , what does that tell us please and what should I do next ?

 

Looks like Right channel is down , locate transistors Q310, 312, 314, 316 and measure the Base and Emitters of these.

Follow the circuit
diagram on Pg 14, and compare the readings.

 

Looks like Right channel is down , locate transistors Q310, 312, 314, 316 and measure the Base and Emitters of these.

Follow the circuit
diagram on Pg 14, and compare the readings.

Thanks Dodgydave, I will take those measurements tomorrow and report. All the best

 

Also take a look at adjustment trimmers VR301 and VR302 and draw (or photograph) the set position of these two trimmer resistors. Write down the position of the trimmer, e.g. 10 o'clock. Do not change the settings.

Locate resistors on the amplifier board:
R304
R302
R312

Carefully (don't short your meter probes to any other point) measure the voltage with respect to GND on the LEFT leg and again on the RIGHT leg of each resistor. (Volume at 0, no speakers, power ON).

R304 LEFT LEG =
R304 RIGHT LEG =
R302 LEFT LEG =
R302 RIGHT LEG =
R312 LEFT LEG =
R312 RIGHT LEG =

 

Thank you both. I really appreciate all your guidance, and I’ll be able to take these measurements later today and report back.

 

Here is the photo of VR301 and VR302. I would say the position of both trimmers is identical at 8.10 clock hands position.

Here are the voltage readings for the transistors - these voltages were not steady but kept changing as I held the probe on the circuit
Q310 B is 4.4V and E is 4.9V
Q312 B is 12.5V and E is 12.5V
Q314 B is 8.2V and E is 8.7V
Q316 B is 14-16V and E is 13-15V

Here are the resistor readings, I measured these twice in a ten minute interval and all voltages had shifted by 2V each in that period, more negative
R304 L is -39.0V and R is -38.1V
R302 L is -20.2V and R is -38.1V
R312 L is -38.9V and R is -39.2V

 

Definitely something not right with Q316.. should be Negative reading, can you check Q306 and Q308 B/E readings.

 

Ok, Q306 B is 10.4V and E is 11.4V, Q308 B is 5.4V and E is 5.2V

 

Forgot to attach the photo of the trimmers, here it is

 

Q308 Base should be at -2V, looks like Q304 isn't turned on enough or the preset Vr302 and Q302 are faulty.

Does the voltage alter when you adjust Vr302 on Q308 Base..?

 

Q308 Base should be at -2V, looks like Q304 isn't turned on enough or the preset Vr302 and Q302 are faulty.

Does the voltage alter when you adjust Vr302 on Q308 Base..?

I’ll try these new measurements tomorrow and report back. Many thanks !

 

Many of your voltages are way off including the supply voltages. Usually one of the first things we check is the supply voltages. I assumed that you had already done that. Perhaps I read that on a different thread.

Measure the positive and negative supply with respect to GND.

+V at the cathode of D403 or D404 (shown in red)

-V at the anode of D401 or D402 (shown in purple)

Be very careful here. You are expecting to see +54V and -54V. One slip and you and the amp are toast.

Make sure that you always read and record positive and negative signs correctly.

 

Many of your voltages are way off including the supply voltages. Usually one of the first things we check is the supply voltages. I assumed that you had already done that. Perhaps I read that on a different thread.

Measure the positive and negative supply with respect to GND.

+V at the cathode of D403 or D404 (shown in red)

-V at the anode of D401 or D402 (shown in purple)

Be very careful here. You are expecting to see +54V and -54V. One slip and you and the amp are toast.

Make sure that you always read and record positive and negative signs correctly.

View attachment 224912

Hi MrChips. I did not take any voltage rail measurements before, but I took them just now. They are:
at D402 (RED point) is +39.8.4V
at D402 (PURPLE point) is -39.8.4V

 

Hi MrChips. I did not take any voltage rail measurements before, but I took them just now. They are:
at D402 (RED point) is +39.8.4V
at D402 (PURPLE point) is -39.8.4V

In case it is relevant, I am using as my GND point the external GND terminal on the rear of the AM, next to the Phono inputs, which makee it easier for me to hold the GND probe steady whilst I measure with the DMM Input probe