Marantz 2325 Losing Right Channel Input Before Pre

[richardg0n]

Greetings AK,

I am losing the right channel input before the pre(PE01) regardless of input(PHONO, FM, AUX).

The unit was recapped/restored, including replacing broken Pre and Main RCA inputs in the rear, recapped Power Supply(P800), Phono(P400), Buffer Amp PH01, Dolby-Tone-Meter(PL01), Pre-board(P800), Multipath board(PU01), and Left and right amps(P700).

This issue happens shortly after the unit is turned on and warms up. The right input fades into silence(sounds like a transistor issue). I isolated the problem crossing the RCA Main and Pre Jacks in the back and am only getting input from the Left side Pre RCA. The Left and right amps are working when receiving input from the left Pre.

Troubleshooting so far:

Sending 1k tone to AUX and checking for input at right Pre(PE01) pin 8 - Input is lost after five minutes but still receiving left input signal on pin 7.

Cheked power at pin 10(PE01) after input loss - 35V

The input returns on pin 8(PE01) when engaging the Hi-pass filter on PU01 or S003 Mode Switch when switching to anything except for the right.

Looking at the schematic, pin 8(PE01) input runs through PU01 first. Thinking it may be a bad transistor, I Replaced all the transistors on PU01 except for HU01/HU02(I didn't have replacement parts but checked them with Peak atlas DCA55). All caps in PU01 were also replaced.

Any troubleshooting ideas or direction would be greatly appreciated. Thank you!

 

[AE Bob]

If the issue only occurs after the unit warms up, try using freeze spray.

 

[richardg0n]

If the issue only occurs after the unit warms up, try using freeze spray.

SOLVED! Connected oscilloscope to right main speaker terminal and sent 1k signal to AUX. Used freeze spray on three boards until I found the problem. Bad resistor and two transistors later and the 2325 is ready for a new home.

Thank you Bob!

 

[runningdog]

That's awesome! Which board had the bad resistor? The only electronics between the AUX inputs and the preamp inputs is the PH01 buffer amplifier, I see the PH01 board in your pic with the transistors that were replaced, is that where the bad resistor was?

The interaction with the Hi Filter switch is really interesting to me.as I am stuck on a 2325 (in a different thread and not meaning to hijack this thread) that distorts unless the Hi Filter is engaged.

 

[richardg0n]

That's awesome! Which board had the bad resistor? The only electronics between the AUX inputs and the preamp inputs is the PH01 buffer amplifier, I see the PH01 board in your pic with the transistors that were replaced, is that where the bad resistor was?

The interaction with the Hi Filter switch is really interesting to me.as I am stuck on a 2325 (in a different thread and not meaning to hijack this thread) that distorts unless the Hi Filter is engaged.

Yes, PH01. The culprits were a scorched resistor at CH28 and the transistors at HH09 and HH10. My guess is someone had previously installed the CAP at CH13 with the polarity reversed because of the known silkscreen error on the board which damaged the resistor and transistors. I recently made a mistake and forgot to reverse the cap at CH13 when installing and burned up CH28 on another 2325.