I have this old amplifier that needed a bit of work.
The sound output was a bit crunchy on one channel and there was a of lot cold solder joints.
I decided to refresh it and make it reliable for everyday use so I resoldered cold joints and replaced all electrolyte capacitors
The problem is that the amp after resoldering does not play. There is no protection led, but I think it's in protection mode.
After that I replaced
- TL494
- TL072 (instead of ba4558)
- IRFZ44 as per schematic instead of 50n06 that were originally on the board
- rectifiers
- TIP41 and 42
Both BA4558N are ok, sound goes to the R153. After I think that is grounded as there is 1.12v on the pin 1 of the U1 optocoupler.
There is 1.8v measured between the supply ground and signal ground.
Square wave is ok, but the rail voltages are a different: +33.3v and -29.5v. 16v voltages are +16.6 are -13.6v.
Input voltage is 12v.
Output transistors are ok, 1n4148 diodes are ok. I checked many resistors and they are within the spec. There is no voltage on speaker terminals.
Here's the schematic diagram https://elektrotanya.com/magnat_traxx_660_sch.pdf/download.html
What should I do next?
The sound output was a bit crunchy on one channel and there was a of lot cold solder joints.
I decided to refresh it and make it reliable for everyday use so I resoldered cold joints and replaced all electrolyte capacitors
The problem is that the amp after resoldering does not play. There is no protection led, but I think it's in protection mode.
After that I replaced
- TL494
- TL072 (instead of ba4558)
- IRFZ44 as per schematic instead of 50n06 that were originally on the board
- rectifiers
- TIP41 and 42
Both BA4558N are ok, sound goes to the R153. After I think that is grounded as there is 1.12v on the pin 1 of the U1 optocoupler.
There is 1.8v measured between the supply ground and signal ground.
Square wave is ok, but the rail voltages are a different: +33.3v and -29.5v. 16v voltages are +16.6 are -13.6v.
Input voltage is 12v.
Output transistors are ok, 1n4148 diodes are ok. I checked many resistors and they are within the spec. There is no voltage on speaker terminals.
Here's the schematic diagram https://elektrotanya.com/magnat_traxx_660_sch.pdf/download.html
What should I do next?
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I'm not 100% sure, there is no protection led.
If it's in protection mode there would be no square wave coming out of 494?
If it's in protection mode there would be no square wave coming out of 494?
In protection, I wouldn't expect to see the drive from the 494.
Do you have a scope?
What are you using for a signal source?
Do you have a scope?
What are you using for a signal source?
Yes, I have a scope. I use scope's internal signal generator.
I checked on two other amplifiers schematics. Pin 3 of the 494 goes to the protection led.
When I connect the remote wire, pin 3 raises to 4v for 2 seconds and then falls to 0.
That should signify that there are no errors and the PS is not in protection.
I checked on two other amplifiers schematics. Pin 3 of the 494 goes to the protection led.
When I connect the remote wire, pin 3 raises to 4v for 2 seconds and then falls to 0.
That should signify that there are no errors and the PS is not in protection.
With no RCAs plugged into the amp, what's the resistance from the input RCA shields to the primary ground terminals?
Do you see the input signal on pins 1 and 7 of IC3?
The amp doesn't appear to be in protection.
Do you see the input signal on pins 1 and 7 of IC3?
The amp doesn't appear to be in protection.
Resistance is 1.05 kΩ
Yes, there is signal on those pins. Signal disappears after the R153.
I also measured voltage on the pin 1, IC22. 1.3v when the remote is connected.
Yes, there is signal on those pins. Signal disappears after the R153.
I also measured voltage on the pin 1, IC22. 1.3v when the remote is connected.
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Remove the bridge.
Remove Q116 and Q216, one at a time, to see if having either out of the circuit allows audio to pass.
Also confirm that the emitter resistors are within tolerance.
Remove Q116 and Q216, one at a time, to see if having either out of the circuit allows audio to pass.
Also confirm that the emitter resistors are within tolerance.
Removed both transistors, no change.
Resistors are 4.6 Ω
I noticed that R601, located before TIP41 is very warm.
Resistors are 4.6 Ω
I noticed that R601, located before TIP41 is very warm.
Recheck the resistors (and your meter). The resistors are supposed to be 0,1 ohm.
DC voltage on pins 1 and 7 of IC22?
DC voltage on pins 1 and 7 of IC22?
Sorry, I thought you meant Q116 / Q216 emitter resistors.
Output emitter resistors are ok, 0.1Ω.
Pin 1 1.32v
Pin 7 1.35v
Output emitter resistors are ok, 0.1Ω.
Pin 1 1.32v
Pin 7 1.35v
Lift D21 and D22, one at a time. Does having either of those out of the circuit allow the amp to pass audio?
I lifted D21 once before, no change.
Now I lifted D22 and it works!
I replaced D22 and D23 and now the amplifier is fully functional.
Thank you for your guidance.
Now I lifted D22 and it works!
I replaced D22 and D23 and now the amplifier is fully functional.
Thank you for your guidance.