Voltages at TP401, TP501 and TP502.

If you measure voltages close to 0V (no greater that 50mV) you can proceed to a sound check with speakers.
You don't need Q515 and Q517 to do this test.
Keep the volume level low. After 2 minutes do a quick check with the thermal camera and finger touch.

 

I checked the voltages.

TP501:
- to GND: OL.
+ to GND: -5.5 mV
+/-: OL.

TP502:
- to GND: -6 mV
+ to GND; -6 mV
+/-: 0 V

TP401:
RIGHT +/- : +10 mV
LEFT +/- : +13 mV


So i checked with sound... on LEFT channel the sound is distorted.
It is not distorted at RIGHT channel.

But i let it play for 5 minutes..... i can't see no other hot spots than earlier.....
It is the small transistors Q413,Q415,Q414,Q416 that obtain some heat... same with playing as with idling... they are about 50 degrees celcius

 

I checked the voltages.

TP501:
- to GND: OL.
+ to GND: -5.5 mV
+/-: OL.

Check the voltages again with the meter range raised so that you can get a valid reading.

Do you sinewave test at 400Hz with your signal generator and oscilloscope and measure waveform at TP501 and TP502.

 

Check the voltages again with the meter range raised so that you can get a valid reading.

Do you sinewave test at 400Hz with your signal generator and oscilloscope and measure waveform at TP501 and TP502.

Sorry, stupid me, i thought i did, but didn't get anything...but i just raised it one up, which wasn't enough.

Voltage at TP501:
- to GND: -5.1 Volt
+ to GND: -7 mV
+/- : -5.1 Volt

That's not right.......

It is -5 V in at Q509 Base, i checked R517 resistor, ok, -5 V at Q505 Emitter and Base, i checked R513 and R511, measured ok in circuit, I measured -5 V at Base and Emitter at Q501, i checked R501,R503,R465,R461,R509 measured ok in circuit.
I might be looking at the wrong places, just tried to see if i could find something

 

Work your way along the LEFT channel and see where the voltages don't match with the circuit or with the RIGHT channel, bear in mind that the supply voltage is now around ±48V.

 

I have measured voltages at all transistors in X4 LEFT channel, it seems ok, slightly lower voltages then in RIGHT channel, like it has been but i find one point where it's not correct

At IC401 pin 1. i measure -0.1 Volt, it's supposed to be +1.3
Compared to
IC402 pin 7, here i measure +1.3 V like it's shown in the schematic.

Seems like R431 goes open when energized, tests ok in circuit.. measured +7 V at one side at -0.1 V at the other side, compared to RIGHT channel R432 has +1.2 volt at both sides..

I guess it doesn't have to do with the -5 V problem.... but it's the deviation i could find..

 

What are the voltages on both legs of R427 and R428?

 

What are the voltages on both legs of R427 and R428?

R427: +7 V / +1.2 V
R428: +7.6 V / +1.1 V

 

This is not consistent with what you wrote in post #726.
You said R431 is showing +7V on one side and -0.1V on the other side.
R427 and R431 share a node which ought to be about 1.3V not +7V.

 

This is not consistent with what you wrote in post #726.
You said R431 is showing +7V on one side and -0.1V on the other side.
R427 and R431 share a node which ought to be about 1.3V not +7V.

Sorry. you are correct, I messed up the reading there! i might edit the post

Here are the correct readings, the minus voltage seems to vary a little, less after more power on/off (it was -0.1 V at R431/PIN1 in post #726)

R431: +1.24 V / -0.25 V
R432: +1.13 / +1.10

 

hmm.. how would we get further on this, my knowledge is not enough..

I have checked voltages around a little more..
Noticed at IC401 PIN4, i measure -7 Volt, if i follow in the schematic it goes through two resistors,
first R461, measures -7 V / -5.9 V, then R465 measures -5.9 V / -5.6 V and the -5 Volt is altso at Q501 Base and follows out to the X5 circuit. Checked the resistors, they measure ok in circuit, but what component should lower the voltage from -7 to -0.5 at Q501 ?

I checked at R462, measures - 7.6 V / -1.1 V

Also comparing R463 and R464 they measure very different.. kind of hard to see what the voltage should be out of IC401/402 at that point..

R463: -4.4 V / -4.7 V
R464: +1 V / +1 V

Are you getting tired of this thread MrChips? hehe

 

This amplifier is DC coupled, i.e. a voltage on the input produces a voltage on the output.
All DC coupled amplifiers require negative feedback. Without negative feedback the output would not stabilize and will hit the power rails.

I am conducting circuit simulation to find out where is the most likely place for the imbalance.
Negative feedback is provided via IC401 pin-2 and IC401 pin-6.

Let us repeat the voltage measurements and compare the LEFT and RIGHT channels.
Measure voltages at
TP401
L CH +
L CH -
R CH +
R CH -

TP501 +
TP501 -
TP502 +
TP502 -


IC401 Pins
1
2
3
4
5
6
7
8

IC402 Pins
1
2
3
4
5
6
7
8

 

All voltages measured to GND

TP401
LCH+: 0 V
LCH-: 0 V
RCH+: 0 V
RCH-: 0 V

TP501+: 0 V
TP501-: -5 V

TP502+: 0 V
TP502-: 0 V

IC401:
1: -0.15 Volt
2: 0 V
3: 0 V
4: -7.15 V
5: 0 V
6: 0 V
7: -4.7 V
8: +7 V

IC402:
1: +1 V
2: 0 V
3: 0 V
4: -7.6 V
5: 0 V
6: 0 V
7: -1.1 V
8: +7.7 V

 

Thanks for the readings.

Voltages at TP502 are good.

Voltages at TP501 are bad and not right. There is R547 + R549 across TP501, a total of 0.44Ω.
If you have 5V across TP501 then you have about 11A flowing through R547 and R549.

Check the resistance of R547 and R549 while sitting in-circuit (with power OFF).

With power ON, measure the voltage at each leg of R547 and R549 with respect to GND.

 

Measured R547 and R549 in circuit

R547: 0.2 ohm
R549: OL. seems to be open

Voltage reading
R547: 0 V / 0 V
R549: 0 V / -5 V

 

Ok. Replace R549 and repeat the tests.

 

While you're at it you should also measure the resistance or R569 and R571 while in-circuit (with power OFF).

 

Okey, so R549 was open, and also R569 had a little higher value then it should have, so i replaced R549 and R569.

But before further testing i made a little mistake i need to check with you first.

Sometimes when i have the board out, i forget to connect the power connectors to it CP606/CP607 before powering up, and to avoid a spark when connecting them as i have experienced earlier i like to drain the power supply capacitors.

I have another 100W bulb i have soldered cables to, and with power off i connect them to the CP607 plug and i drain the capacitors.
When i did this now, i didn't notice my soldered cable at the socket of the bulb had fell off, so i made a short circuit at the bulb, it threw a pretty good spark..hehe.. stupid me! I haven't checked the schematics yet, but if the cables goes directly to the capacitors i might not have damaged anything? Power was of course off..

 

I think you’ll be fine.
Go ahead and measure the voltages at TP401, TP501, TP502.

 

It was fine
Power ON.

Looks like the negative 5 volts has disappeared

Measured to GND:

TP501+: 0 V
TP501-: 0 V

TP502+: 0 V
TP502-: 0 V

TP401:
LCH-: 0 V
LCH+: 0 V

RCH-: 0 V
RCH+: 0 V