Yes.....diodes D503.....D504....D505......D506
was dead.
No 24v.
After replacing no protect.
Only big white noise on preamp volume zero .
On all sources
was dead.
No 24v.
After replacing no protect.
Only big white noise on preamp volume zero .
On all sources
Last edited:
1. Disconnect the amplifier section (green lines)
2. Short 2 and 3 (green circles)
3. Do not have anything connected to the amplifier output (just remove F2 🙂)
4. Measure the voltage drops across: [R404, R406 & R407] [R420 & R419] and [R422 & R423] (write them on the circuit diagram that I attached below).
5. Check the voltage readings that I highlighted in blue - measure those test points and report back (write them on the circuit diagram that I attached below).
Good luck, don't short anything with the probes while taking the measurements !!
2. Short 2 and 3 (green circles)
3. Do not have anything connected to the amplifier output (just remove F2 🙂)
4. Measure the voltage drops across: [R404, R406 & R407] [R420 & R419] and [R422 & R423] (write them on the circuit diagram that I attached below).
5. Check the voltage readings that I highlighted in blue - measure those test points and report back (write them on the circuit diagram that I attached below).
Good luck, don't short anything with the probes while taking the measurements !!
Last edited:
Ok, that's additional information...
Diode D503 and capacitor C501 combination is your power supply rail for 24V DC. What regulates this rail to be exactly 24V is the Zenner D505.
If D503 and D504 were "dead"(what is dead?? diodes failed open, or failed short / shorted??), then something was shorting these rails in the pre-amp section.
I would focus on one section at a time.... start with the pre-amp section and disconnect the amplifier section fully, i.e. disconnect the power supply to amp sections as well.
Have a look at my previous post... use that as a guide, and then provide the voltage readings for the pre-amp section.
All adjust of power amplifier are ok
Positive and negative power voltages are 40...-40v
DC unbalance .....0v
ICq......15mV on 2 channels
Positive and negative power voltages are 40...-40v
DC unbalance .....0v
ICq......15mV on 2 channels
Yes.
Use a tone generator and start from the beginning... trace the signal and look for the first instance when the signal becomes noisy
There's a phono (MM) section, and tone control - with a pre-amp section.
Use a tone generator and start from the beginning... trace the signal and look for the first instance when the signal becomes noisy
There's a phono (MM) section, and tone control - with a pre-amp section.
White noise is on PIN 3 of 2 channels.
I desoldered all transistors....all ok.
Positive and negative voltage ok.....
Other side of tone board no white noise on pins 201....202....203....204....205.
I desoldered all transistors....all ok.
Positive and negative voltage ok.....
Other side of tone board no white noise on pins 201....202....203....204....205.
I understand that completely....
You have two options:
try to bypass the tone control and pre-amp section, and use the amplifier as the main amplifier only
or
.. take the amplifier to service and see if they can figure out where exactly the problem is
Good luck
I'm not used to retreating. I repaired quite a few amplifiers This circuit is easier to trace the audio signal. I will take this unit out and turn on the power. can you draw the signal path again on this diagram please
Red is the "main" signal from the volume potentiometer
Blue is the feedback signal to differential pair transistor and to tone volume potentiometers (via switches). The amplified main signal is used as a feedback signal
Good luck
Blue is the feedback signal to differential pair transistor and to tone volume potentiometers (via switches). The amplified main signal is used as a feedback signal
Good luck
I can not locate those 2 diodes...
Anyway, there are 3 DC rails, 24V each. They have to be clean...