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Marantz SR440 tuner

I got a Marantz SR 440 in for repair with no display. The 12 volt 3 terminal regulator was out, and i replaced it and the 12 volt rail came back to life. AFter the replacement, the front panel display came back to life, But, the unit randomly locks up where you cannot change the radio channel. other times it works ok. I don't have a print on this yet, but the power rails seem to be ok. Quick EST check shows OK. I resoldered anything that looked suspicious. Any tips on this old beast? The front panel CPU supply shows 4.85 volts with little ripple.

Bob

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Reply to
Bob Urz
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I think I'd look to the front panel itself - a tact switch leaky or partially pressed, inhibiting the front panel function. A leaky capacitor on the front panel could do the same thing. Also check the crystal, it could be cutting out, and the reset line, if you can find it. Could be getting pulled down somewhat.

Mark Z.

Reply to
Mark D. Zacharias

Switches seem to feel ok. No mushy ones or partially depressed ones. The CPU does seem to be going in LA LA land somehow. If i had the print i could track down the reset pin and find out how its done. I did not see a dedicated chip on the front panel that does it. I wonder if the

4.85 volts is too low. It seems to be a simple zenar regulator.

Bob

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Reply to
Bob Urz

Well. i think i fixed it. on the tuner board (not front panel control board) there was a steel land that grounded the board to the chassis. i cleaned and retorqed it and it seemed to keep working. Then i soldered it.

Bob

Bob Urz wrote:

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Reply to
Bob Urz

Sounds like a home run. Let's keep our fingers crossed.

Mark Z.

Reply to
Mark D. Zacharias

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