Stage Line 500W amp repair, help please

Thread Starter

Rookieme

Joined Jan 26, 2021
308
New BA546 IC is in, no fans on when powered up, going to run it at lo power and let it warm up and see what happens
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
So it seems the left chanel gets hot faster than the right, but no fan at all now, not sure how hot to let this get
 

R!f@@

Joined Apr 2, 2009
9,781
Compare channel biasing value.
You could scope for oscillations too.

There should be a temp sensor mounted or touching the sink. If not then it starts at certain output volume
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
I was under the impression that Q16 and Q42 were the temp sensors for the fan control, however, shorting there base to 0v activates the thermal protect but does not activate the fan, also on the left chanel this only activates the warning LEDs, on the right this activates the LEDs and kills the output completely,
The left chanel heat sink is getting hot even without being driven by any input
 

LesJones

Joined Jan 8, 2017
3,701
For the left hand channel measure the following voltages with respect to 0 volts both with and without Q16 base shorted to
0 volts.

Q54 base
Q54 collector
Q2 base
Q2 emitter
Q2 collector
Q3 base
Q3 collector
Q3 emitter

IC3 pin 1
Q50 base
Q50 collector
Q50 emitter

For the left right channel measure the following voltages with respect to 0 volts both with and without Q42 base shorted to
0 volts.

IC3 pin 7
Q50 base
Q50 collector
Q50 emitter

Measure the voltage between Q22 base and Q1 base
Measure the voltage between Q40 base and Q23 base

Post the results of these tests.

Les.
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
ok les this is what I get

For the left hand channel measure the following voltages with respect to 0 volts both with and without Q16 base shorted to
0 volts.
Left channel Q16 base not grounded to 0V


Q54 base =0.160 vdc
Q54 collector =7.188 vdc
Q2 base =0.635 vdc
Q2 emitter =0.000 vdc
Q2 collector =0.109 vdc
Q3 base = 74.70 vdc
Q3 collector = 75.34 vdc
Q3 emitter = 75.42 vdc

IC3 pin 1 = 23.51 vdc
Q50 base = 23.90 vdc
Q50 collector = -26.23 vdc
Q50 emitter = 24.52 vdc

Left channel Q16 base grounded to 0V
Q54 base =0.695 vdc
Q54 collector =0.008 vdc
Q2 base =0.008 vdc
Q2 emitter =0.000 vdc
Q2 collector =76.35 vdc
Q3 base =76.98 vdc
Q3 collector =-5.569 vdc
Q3 emitter = 76.66 vdc
ICE pin 1 = 23.71 vdc
Q50 base = 24.10 vdc
Q50 collector = -26.68 vdc
Q50 emitter = 24.75 vdc

For the left right channel measure the following voltages with respect to 0 volts both with and without Q42 base shorted to
0 volts.


Right channel Q42 base not grounded to 0v

IC3 pin 7 = 23.85 vdc
Q50 base = 24.21 vdc
Q50 collector = - 26.62 vdc
Q50 emitter = 24.90 vdc

Right channel Q42 base grounded to 0v
IC3 pin 7 = 23.96 vdc
Q50 base = 24.25 vdc
Q50 collector = - 26.65 vdc
Q50 emitter = 24.95 vdc

Q22 base and Q1 base =0.00 vdc with Q16 base grounded to 0v and 4.17 vdc with Q16 not grounded


Q40 base and Q23 base =0.00 vdc with Q16 base grounded to 0v and 4.22 vdc with Q16 not grounded
 
Last edited:

LesJones

Joined Jan 8, 2017
3,701
The first tests that goes up to Q3 collector is to understand why an over temperature condition is not shutting down the left hand channel. The circuit is working as it should up to Q3 collector. We will need more tests to sort this out but will leave this until later.

The tests around IC3 are to understand why the fan is not coming on when an over temperature condition is simulated by shorting Q16 or Q42 base to emitter. The outputs of IC3 are not going low when they should do. We need to do some test on the inputs of Q3 to sort this out. So do these tests.

For left hand channel.
measure the voltage on the following pins of IC3 with Q16 base emitter junction not shorted and then shorted
Pin 2
Pin 3
Pin 4
Pin 7

For right hand channel.
measure the voltage on the following pins of IC3 with Q42 base emitter junction not shorted and then shorted
Pin 6
Pin 5
Pin 4
Pin 7

The tests between Q22 and Q1 base and between Q40 and Q23 are to understand why the left hand channel is running hotter than the right hand channel. More tests are required to sort this out. We will deal with this later.

Do the tests for the fan problem.

Les.
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
Here are the results of the tests you requested,


Left channel Q16 not shorted

IC3
pin 2 = 0.571 vdc
pin 3 = 14.78 vdc
pin 4 = - 15.02 vdc
pin 7 = 0.157 vdc

Left channel Q16 shorted

IC3
pin 2 =0.000 vdc
pin 3 = 0.508 vdc
pin 4 = 0.002 vdc
pin 7 = 0.156 vdc

Right channel Q42 not shorted

pin 6 = 0.663 vdc
pin 5 = 0.483 vdc
pin 4 = 0.002 vdc
pin 7 = 0.159 vdc

Right channel Q42 shorted

pin 6 = 0.000 vdc
pin 5 = 0.509 vdc
pin 4 = 0.002 vdc
pin 7 = 6.665 vdc

pete
 

LesJones

Joined Jan 8, 2017
3,701
I think that you have IC3 inserted the wrong way round or you are counting pin numbers incorrectly.
The voltage readings make no sense. Pin 4 is the negative 15 volt power rail so I would have expected it to remain at about -15 volts at each of the 4 time that you tested it. (I made a mistake putting pin 7 down as the positive 15 volt power rail I should have said pin 8) This is a link to the BA4560 datasheet so that can confirm the way the pins are numbered. The view of the IC is from above in the datasheet. If you have inserted it the wrong way round you have probably destroyed it as the supply pins would be reversed.

Les.
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
I think that you have IC3 inserted the wrong way round or you are counting pin numbers incorrectly.
The voltage readings make no sense. Pin 4 is the negative 15 volt power rail so I would have expected it to remain at about -15 volts at each of the 4 time that you tested it. (I made a mistake putting pin 7 down as the positive 15 volt power rail I should have said pin 8) This is a link to the BA4560 datasheet so that can confirm the way the pins are numbered. The view of the IC is from above in the datasheet. If you have inserted it the wrong way round you have probably destroyed it as the supply pins would be reversed.

Les.
i am fairly confident its installed the correct way round, as i used an IC socket i can refit the old one and the fan comes back on, i am also counting the pins correctly, would you like me to do the test again but this time use pin 8 and not 7?

cheers
 

LesJones

Joined Jan 8, 2017
3,701
I have corrected the +15 volt test pin but I have also added two extra test points.
Also try these tests with nothing plugged into the socket.
I have just seen your post #512. The socket is fitted correctly.

For left hand channel.
measure the voltage on the following pins of IC3 with Q16 base emitter junction not shorted and then shorted
Pin 2
Pin 3
IC4 pin 2
Pin 4
Pin 8

For right hand channel.
measure the voltage on the following pins of IC3 with Q42 base emitter junction not shorted and then shorted
Pin 6
Pin 5
IC4 Pin 6
Pin 4
Pin 8

Did you buy the BA4560 from a reputable supplier ? I am wondering if the items supplied could be some other device remarked as BA4560.

Les.
 
Last edited:

Thread Starter

Rookieme

Joined Jan 26, 2021
308
I have corrected the +15 volt test pin but I have also added two extra test points.
Also try these tests with nothing plugged into the socket.
I have just seen your post #512. The socket is fitted correctly.

For left hand channel.
measure the voltage on the following pins of IC3 with Q16 base emitter junction not shorted and then shorted
Pin 2
Pin 3
IC4 pin 2
Pin 4
Pin 8

For right hand channel.
measure the voltage on the following pins of IC3 with Q42 base emitter junction not shorted and then shorted
Pin 6
Pin 5
IC4 Pin 6
Pin 4
Pin 8

Did you buy the BA4560 from a reputable supplier ? I am wondering if the items supplied could be some other device remarked as BA4560.

Les.
No I did not by from a reputable supplier, it was an amazon purchase, I did get 10 of them and have tried another with the same results,

Will do these tests and posy my results
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
ok this is what i get

left channel Q16 not shorted-IC3 IN
IC3
pin 2 = 0.570 vdc
pin 3 = 14.76 vdc

IC4
pin 2 = 14.61 vdc
pin 4 = 0.002 vdc
pin 8 = 14.82 vdc

Right channel Q42 not shorted-IC3 IN

IC3
pin 6 = 0.568 vdc
pin 5 = 0.654 vdc

IC4
pin 6 = 0.650 vdc
pin 4 = 0.002 vdc
pin 8 = 14.81 vdc


Left channel Q16 shorted-IC3 IN

IC3
pin 2 = 0.577 vdc
pin 3 = 0.000 vdc

IC4
pin 2 = 0.000 vdc
pin 4 = 0.002 vdc
pin 8 = 14.80 vdc

Right channel Q42 shorted-IC3 IN

IC3
pin 6 = 0.576 vdc
pin 5 = 0.000 vdc

IC4
pin 6 = 0.000 vdc
pin 4 = 0.002 vdc
pin 8 = 14.80 vdc


left channel Q16 not shorted IC3 REMOVED

IC3
pin 2 = 0.574 vdc
pin 3 = 14.75 vdc

IC4
pin 2 = 14.75 vdc
pin 4 = 0.000 vdc
pin 8 = 14.79 vdc


Right channel Q42 not shorted IC3 REMOVED

IC3
pin 6 = 0.568 vdc
pin 5 = 0.648 vdc

IC4
pin 6 = 0.648 vdc
pin 4 = 0.002 vdc
pin 8 = 14.79 vdc
 
Last edited:

LesJones

Joined Jan 8, 2017
3,701
From the way you you have shown the results in post #515 I think you may have misunderstood (Or I was not clear enough.) in post #514. I think after taking the readings on pins 2 & 6 of IC4 you have taken the readings on pins 4 and 8 of IC4 rather than IC3.
I think there is a problem with the -15 volt supply to pin 4 of IC3. In previous posts the reading on IC3 pin 4 has been close to zero volts except for the first reading in post #509 when it was close to -15 volts. You need to investigate the cause of this.

The reading of close to + 15 volts on IC3 pin3 / IC4 pin2 indicates that Q16 base emitter junction is open circuit OR it's emitter lead is not connected to zero volts. You also need to investigate this problem.

Les.
 
Hello, probably Q26 reads dead short circuit from bass to emitter but I'm not sure so try it and it should work as it should. Regards and let me know if I helped later
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
From the way you you have shown the results in post #515 I think you may have misunderstood (Or I was not clear enough.) in post #514. I think after taking the readings on pins 2 & 6 of IC4 you have taken the readings on pins 4 and 8 of IC4 rather than IC3.
I think there is a problem with the -15 volt supply to pin 4 of IC3. In previous posts the reading on IC3 pin 4 has been close to zero volts except for the first reading in post #509 when it was close to -15 volts. You need to investigate the cause of this.

The reading of close to + 15 volts on IC3 pin3 / IC4 pin2 indicates that Q16 base emitter junction is open circuit OR it's emitter lead is not connected to zero volts. You also need to investigate this problem.

Les.
please see post #515 again,

not sure why but i do now have 15vdc at pin 3 on IC3

all other readings are correct
 

LesJones

Joined Jan 8, 2017
3,701
Having +15 volts on IC3 pin 3 indicates that either the base emitter junction of Q16 or it's emitter is not connected to zero volts. This will mean that over temperature will not be detected on the left hand channel. (You had a similar problem with the emitter connection of Q42 at around post #396.)
What was causing the loss of -15 volts on pin 4 of IC3 ? When you say "all other readings are correct" do you mean that the fan now works when shorting the base to emitter on either Q16 or Q42 ? ( When you are shorting the base to emitter of Q16 you may also be making contact between the emitter on the 0 volt track.)

Les.
 

Thread Starter

Rookieme

Joined Jan 26, 2021
308
OK chanced my arm and replaced the Ba4560 IC3 for a TL032 opamp i had lying around,
so now the fan works when Q16 or Q42 is shorted to 0v, i think the ba4560s i got are duff
 
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