Marantz 4400 Troubleshooting Help

[Brent Davis]

Greetings, I am hunting down a short in my marantz 4400 but needed to turn here for some help. Here are the steps and results I had gotten so far with replacing components and my dim bulb tester:

- Got the unit from a garage sale as "not working." Hooked it up to Dim Bulb and bright as can be.
- Refurbished the P800 power supply then hooked it up to DBT......gets bright and then dims down.....but not all the way. Test volume controls and tone controls and none of them respond when turning the knobs. Cleaned the controls......same issue. No response on controls. Very little sound, if any coming out of speakers. I cleaned the remote/local switch.
- Gain on transistors on Tone Amp are low so I restore the PD01 Tone Amplifier. No results as volume and tone controls still wont respond to movement. Dim bulb lights up, then still shows small light.
- Restore the Pre-Amp PE01 (many transistors had low gain...........like 50hfe on a few of them). Tested on the dim bulb before installing the ground wire that goes to chassis. Dim bulb behaves how I want it! Then I attach ground wire to post on the PE01 and dim bulb still shows small light. Still little/no sound coming out of speakers.

- I have restoration kit ready for both the right and left amp boards. I have new filter caps ready to go.

- BUT, did anyone pick up on anything from the above that I should try before I continue to move forward?

 

[ocdecio]

First of all congratulations and kudos on using a DBT.

If you want the light to go totally dim you will need a 300W bulb, the 4400 idles at about 50W. There are no shortcuts with the 4400 and you can be losing signal anywhere and there are lots of places to look such as the little buffer amp board close to the preamp board. The tone board also needs to be looked at.

I would start putting it in quad mode and injecting a 1kHz/150mV signal to Aux/CD on each channel and following where it goes or stops as well. Monitor the Pre-Out RCA outputs with a scope. If you can't get signal on ANY channel that points to a defective power supply failing to deliver 35V to the boards or some other reason one or more of the many boards in the signal path are not being fed.

 

[Brent Davis]

Thank you! Yes, I use a 100W bulb so that would explain the amount of light on the bulb.
Appreciate the feedback and guidance. Ill follow those steps and continue this thread!

 

[Brent Davis]

Thank you! Yes, I use a 100W bulb so that would explain the amount of light on the bulb.
Appreciate the feedback and guidance. I’ll follow those steps and continue this

First of all congratulations and kudos on using a DBT.

If you want the light to go totally dim you will need a 300W bulb, the 4400 idles at about 50W. There are no shortcuts with the 4400 and you can be losing signal anywhere and there are lots of places to look such as the little buffer amp board close to the preamp board. The tone board also needs to be looked at.

I would start putting it in quad mode and injecting a 1kHz/150mV signal to Aux/CD on each channel and following where it goes or stops as well. Monitor the Pre-Out RCA outputs with a scope. If you can't get signal on ANY channel that points to a defective power supply failing to deliver 35V to the boards or some other reason one or more of the many boards in the signal path are not being fed.

Hooked up the scope and 1khz signal through the AUX. I had signs of life! But unhealthy for sure. See photo.

 

[Brent Davis]

All channels were similar