I am not sure if i have either of those resistors, i will have a rummage through my box of bits tomorrow and see what i can find

 

T4 and T9 are the amplifiers ground line. (Marked 0vP) The outputs T5 and T10 seem reasonable.
If you look at the schematic you will notice that The missing components are marked "N.F." (Not fitted.) These are probably fitted in a higher power version of the amplifier.
For the right hand amplifier if you connect the negative of a 1.5 volts cell (AA or AAA) to the 0vP rail and the positive to In - R (The junction of R77 an R69) via a 1.8 or 2.2K resistor I would expect the output of the amplifier to read about -4.5 volts.
The same should happen if this is done to the corresponding points on the left hand channel. If the polaritu of the 1.5 volt cell is reversed the output should go to about +4.5 volts.

Les.

When you say connect the negative to 0vP, is that T4 and T9 ?

 

Ok, replaced Q28 with the old good one, now it powers up with no fault LED,s at all, however F2 LED is on dimm but not blowing the resistor, think i am at the end of my knowlage now lol

Oh and this was down to a faulty fuseable resiater

 

The resistor is not really necessary, it is just to limit the current in case you connect to the wrong place. I suggest not using resistor much below 1K. If we call the value of the resistor that you use RX then the expected output voltage should be about - (12000 x 1.5)/(2000 + RX) (Notice the - sign at the start of the formula. It indicates that the output voltage will be the opposite polarity to the 1.5 volt cell) The 4.5 volts I quoted was based on a 2 K resistor and 1.8K and 2.2K are the nearest standard values.

0vP is just what they call the amplifier ground. (Which may not be connected to the mains safety ground.) This will also be connected to the outer of any coaxial input sockets such as phono or BNC.

Les.

 

Grounds can be confusing at times. On this unit there are numerous points that are at 0V.

T35 from transformer
T21, T26
0V
0VD - digital
0VA - analog
0VREF
Chassis
0VP(L) - T20 - power amp Left Channel
0VP(R) - T22 - power amp Right Channel
T4 - speaker Left Channel
T9 - speaker Right Channel

Eventually they all go back to 0V at T21.
You should confirm this by testing with an ohmmeter on the lowest range with power off.
Confirm that the Chassis shows 0-ohms to any or all of the above and you can use this as your 0V reference for voltage metering.
This should also show continuity with the EARTH pin on your AC power plug.

 

Grounds can be confusing at times. On this unit there are numerous points that are at 0V.

T35 from transformer
T21, T26
0V
0VD - digital
0VA - analog
0VREF
Chassis
0VP(L) - T20 - power amp Left Channel
0VP(R) - T22 - power amp Right Channel
T4 - speaker Left Channel
T9 - speaker Right Channel

Eventually they all go back to 0V at T21.
You should confirm this by testing with an ohmmeter on the lowest range with power off.
Confirm that the Chassis shows 0-ohms to any or all of the above and you can use this as your 0V reference for voltage metering.
This should also show continuity with the EARTH pin on your AC power plug.

That is very helpfull, thank you

 

If you are getting close to 0V at the channel outputs T5 and T10 that is good. That is what we are hoping to get.
The next step would be to do a signal test. For this, you will connect a signal source to the inputs. Now is the time to find a PC audio amp, single channel will do. Also see if you can find a cheap speaker that you don't mind destroying.

You will also need a small electrolytic capacitor, 10-100μF will do (almost any voltage 16-50V).

 

@MrChips
Keep it up.

 

The resistor is not really necessary, it is just to limit the current in case you connect to the wrong place. I suggest not using resistor much below 1K. If we call the value of the resistor that you use RX then the expected output voltage should be about - (12000 x 1.5)/(2000 + RX) (Notice the - sign at the start of the formula. It indicates that the output voltage will be the opposite polarity to the 1.5 volt cell) The 4.5 volts I quoted was based on a 2 K resistor and 1.8K and 2.2K are the nearest standard values.

0vP is just what they call the amplifier ground. (Which may not be connected to the mains safety ground.) This will also be connected to the outer of any coaxial input sockets such as phono or BNC.

Les.

Will one of these do ?

 

Yes. That should give a voltage reading between the output and 0vP of about 3.6 volts.

Les.

 

T4 and T9 are the amplifiers ground line. (Marked 0vP) The outputs T5 and T10 seem reasonable.
If you look at the schematic you will notice that The missing components are marked "N.F." (Not fitted.) These are probably fitted in a higher power version of the amplifier.
For the right hand amplifier if you connect the negative of a 1.5 volts cell (AA or AAA) to the 0vP rail and the positive to In - R (The junction of R77 an R69) via a 1.8 or 2.2K resistor I would expect the output of the amplifier to read about -4.5 volts.
The same should happen if this is done to the corresponding points on the left hand channel. If the polaritu of the 1.5 volt cell is reversed the output should go to about +4.5 volts.

Les.

I assume i will have to reinstall Q28 for this test ?

 

Attached the battery and a 3k resister to the left chanel as advised by @LesJones
Black probe on T26 chassis, red probe on T5 meter reads --3.064vdc

 

Reinstalled Q28 and repeared the test for the right chanel, meter reads --3.008

 

I had not realised that you did the previous tests with missing components. Are there any other missing components ? We need to know the ACTUAL schematic, not just the schematic as it should be.

Les.

 

I had not realised that you did the previous tests with missing components. Are there any other missing components ? We need to know the ACTUAL schematic, not just the schematic as it should be.

Les.

No everyting that should be fitted is now fitted

 

In my quick calculation of the expected outout voltage I had ignored the effect of R77. adding the effect of that the calculated reading should be 3.2 volts. The actual reading is close enough to that. Repeat the test with the cell reversed. If you get close to + 3.2 volts reading then all of that channel power amplifier is working to some extent. We won't know if it is fully working until we feed it into a dummy load and drive it fully. (Is the rated load impedance 4 ohms in none bridged mode ?)

 

Test repeated with the polarity reversed,
R/C= 3.50vdc
L/C= 3.09vdc

 

I am surprised that there is a significant difference in the readings between the channels as the gain setting resistors (R67 and R79) are 1% tolerance. What voltage output did you get on the left hand channel when injecting a positive signal ?
Edit. I did not realise that you had swapped channels between posts #52 and #53. I thought you had just replaced the missing transistor.
Les.

 

The left chanel was --3.064vdc

 

With the battery attached the o/p voltage seems to slowly climb on the left chanel, not sure if the right side did this