Electronics > Repair

Marantz PMD430 portable cassette recorder - No Audio

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Bargainhunter:
I am having trouble with my Marantz.  I have no output with the Line IN, Line Out, Microphones or tape playback.  I do have the 4.5 volts and the 15 volts.  I do get a mum from the internal speaker when I probe the playback volume control so I know the output amp is working.  I am thinking the trouble may be in the muting circuit.  I have attached the schematic.  Since the sound affects both channels, it must be in a shared circuit.

Any help would be greatly appreciated.
[attach=1][attachimg=1]

floobydust:
What do the VU meters, LED's do? In either Rec or Play.

Bargainhunter:
The meters do not respond in playback or record.  The Rec LED lights on record but the peak LED does not light up even though I had the record level high.
The meter does indicate battery level when the button is pushed.  The Left meter does show a slight movement if I inject a tone at the volume control terminal.
I tried a microphone in the left and right mic inputs with no response.

floobydust:
I first spend a minute or two look for fractured soldering joints, really common in portable gear.
With so much not working, there are a few mute buses to check and it's a bit complicated.
For playback it mutes on either STOP (QU03), FF/REW (QU04), PAUSE (QU02). The VU meters are also muted in STOP. Shorted capacitor CU02 2.2uF/50V at QU03 would leave muting stuck activated as if in STOP mode. Measure the three voltages on QU03 to see if it's on, causing the problem. QU03 collector goes high to activate muting. Or at connector JK02 to see the muting signals there from the PLAY, PAUSE, FF/REW switches.
The mute switches are DTC124 SOT-23 NPN digital transistor with built in resistors.

David_AVD:
For old cassette player with a mechanical operated record function, always clean the record / play switch as they get dirty and oxidised with age and can cause no audio issues. Look for the long skinny switch that has a lever / wire from the record button.

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