I used a 4.7k ohm 10 watt resistor from the RF power supply to chassis ground and it read 41mv across the resistor?

Something doesn't jive here. I assume you disconnected the power to the RF module before installing the 4.7k-ohm resistor.

According to the voltages you supplied in the first diagram, the voltages across the 2.7k-ohm resistor (28) is 24.7 - 9.6V = 15.1V
The current through resistor (28) is 15.1V/2.7k-ohm = 5.6mA
The load represented by the RF module = 9.6V/5.6mA = 1.7k-ohm

Now if you replace the RF module with a 4.7k-ohm resistor, the voltage across this resistor should be
24.7V x 4.7k /(2.7k + 4.7k) = 15.7V

where as you are telling me you are reading 0.041V.

Are you sure it is not a 4.7-ohm resistor?

 

I lifted one leg each on resistor 31 & 37, I measured the input voltage at 9v still but when I measured 39 with one leg lifted it reads 18.6v at the power input? I haven't done resistor 43 yet,I thought I had better tell you about this reading first.

You can reinstall R31, R37 and R39.

Measure the voltages at both legs of R39.

Measure the voltages at both legs of R43.

 

Something doesn't jive here. I assume you disconnected the power to the RF module before installing the 4.7k-ohm resistor.

According to the voltages you supplied in the first diagram, the voltages across the 2.7k-ohm resistor (28) is 24.7 - 9.6V = 15.1V
The current through resistor (28) is 15.1V/2.7k-ohm = 5.6mA
The load represented by the RF module = 9.6V/5.6mA = 1.7k-ohm

Now if you replace the RF module with a 4.7k-ohm resistor, the voltage across this resistor should be
24.7V x 4.7k /(2.7k + 4.7k) = 15.7V

where as you are telling me you are reading 0.041V.

Are you sure it is not a 4.7-ohm resistor?

Sorry,your right its a 4.7 ohm resistor! At first glance it looked right 4.7 with the ohms omega symbol and a K? Ill grab one from in town and get back soon.

 

Sorry,your right its a 4.7 ohm resistor! At first glance it looked right 4.7 with the ohms omega symbol and a K? Ill grab one from in town and get back soon.

No. Save yourself the trouble for the time being. Measure the voltages in post #22.

 

R38 has been replaced. It should be 4.7k-ohm. I see 47k-ohm in your photograph.

 

You can reinstall R31, R37 and R39.

Measure the voltages at both legs of R39.

R38 has been replaced. It should be 4.7k-ohm. I see 47k-ohm in your photograph.

Yay! That resistor was the problem,Thank you for pointing that out Mr Chips and every-one else for their ideas and suggestions too. I don't know how I did that because I usually measure resistors just to be sure before I solder them in? Anyway Ive got 15v now, the radio works,the transistor measures OK. The only other thing is one channel wont balance properly? Should I start another thread to deal with that or continue here?

 

Continue here.

 

OK, I have done everything I could think of to get this problem solved.Il try and describe it the best I can,Ive replaced the balance and volume pots,it didn't make a difference so I cleaned and installed the originals back because they have screw in threads for mounting the radio back in the console. The left channel is working as it should,but with the right channel and the balance set in the middle as it would be normally and if I have the volume turned right down I can still hear it at a moderate level and by turning the balance further to the right it(the balance) acts as a volume pot and gets louder?This was the original problem Ive been trying to fix from the start.Ive re-soldered all the grounding points except for the ones on the chassis itself because my soldering iron isn't up to it and they look alright anyway?Ive gone over the tone and driver boards with a fine toothed comb but I'm missing something somewhere?

 

Hello,

Does the radio have a mono/stereo button?
If so what happens when you press that?

Bertus

 

Hello,

Does the radio have a mono/stereo button?
If so what happens when you press that?

Bertus

Yes it does have a push button Mono-Stereo but nothing happens when I push it in?

 

Hello,

Does the radio have an external audio input?
If so, what happens when put signal in (like from an mp3/ipod etc.).

Bertus

 

What happens if you set the balance to the middle , and short the outer terminals of the balance control together?

 

Hello,

Does the radio have an external audio input?
If so, what happens when put signal in (like from an mp3/ipod etc.).

Bertus

The console is in a shed down the road from me,Ive taken the radio section out to repair it at home.The console has a record player in it but when I played a record on it it did the same thing with the one channel out of wack? All the inputs go to the same place.Radio,record player TV and guitar.

 

What happens if you set the balance to the middle , and short the outer terminals of the balance control together?

I put an alligator clip across the balance terminals, now the sound only comes out of the left channel at moderate to fairly loud ,if I turn the balance pot either left or right the sound cuts out.(it only works in the middle position)The volume pot wont work at all with the clip across the balance terminals.

 

Hello,

As you have two amplifiers, you can compare voltages between them.
You could compare the voltage accross R34 with R36, these should be about the same.
(this would give you the bias current in the amplifiers).
You could also compare the voltage accross R32 and R33.

Bertus

 

Hello,

As you have two amplifiers, you can compare voltages between them.
You could compare the voltage accross R34 with R36, these should be about the same.
(this would give you the bias current in the amplifiers).
You could also compare the voltage accross R32 and R33.

Bertus

I don't know what you mean Bertus,The resistor numbers only go to 17 on the driver boards? Qh,I see what you mean but number 33 is a thermistor? Its bolted to the chassis Ill measure across them and check.

 

Hello,

The mentioned resistors are not on the board, but near the power transistors:

Bertus

 

We can do some extensive signal tracing with the equipment you have.
But it means working on the radiogram in the shed or relocated.
Do you have access to a soldering iron and your computer link to AAC where ever the radiogram is located?
I don't want you to be trekking back and forth to the shed.

Actually, for now the tests involve simple jumpering across two points similar to what Dodgydave has suggested in post #32-34.
You have a jumper wire with alligator clips. Do you have jumper hooks instead?

 

I put an alligator clip across the balance terminals, now the sound only comes out of the left channel at moderate to fairly loud ,if I turn the balance pot either left or right the sound cuts out.(it only works in the middle position)The volume pot wont work at all with the clip across the balance terminals.

Shorting the balance out, puts the same signal into both amps, sounds like the right amplifier is at fault,

 

Assuming that you can work on the system, here is the plan of attack.
You are going to test the integrity of the system using only your ear as your diagnostic tool.

You are going to test:

Left Channel VOLUME control
Left Channel TONE module
Left Channel DRIVER module and AMP

Right Channel VOLUME control
Right Channel TONE module
Right Channel DRIVER module and AMP

BALANCE control

STEP #1

Unsolder the connection feeding into terminal E on both LEFT and RIGHT DRIVER MODULE.

STEP #2

Set BALANCE control to mid point.

Connect jumper wire from terminal E of LEFT DRIVER MODULE to either leg of R28 on LEFT TONE MODULE.
Listen to LEFT channel speaker and verify that VOLUME control works as expected.

Connect jumper wire from terminal E of LEFT DRIVER MODULE to either leg of R28 on RIGHT TONE MODULE.
Listen to LEFT channel speaker and verify that VOLUME control works as expected.

STEP #3

Repeat STEP #2 using jumper to terminal E of RIGHT DRIVER MODULE.
Listen to RIGHT channel speaker and verify that VOLUME control works as expected.

To be continued...