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Marantz 4230 - Epilogue
#16
Yes, this Marantz uses four M8513A-O varistor diodes in parallel with each bias trimpot. They all tested good (out of circuit) with the diode test of my DMM.

Since the bias on the right channel was initially so high, I made initial adjustments to both right channel trimpots to get the bias down. Then, I waited the requisite 30 minutes to let the unit fully warm up, and then made the final adjustments.
--
Ron Ramirez
Ferdinand, IN
Я этого не понимаю
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#17
Well, it's buttoned back up and is now in service next to my workbench, where it has (temporarily) taken the place of my Fisher 432. So far, so good. It is behaving itself and has shown no further inclinations of releasing the magic smoke.

The only issue I notice now? The right channel is louder than the left. Not by a huge amount, but noticeable if the front balance control is set to the very center. Moving it somewhat to the left balances the channels.

The left channel audio amp board still has all of its original transistors, only the electrolytics have been replaced and three of the film caps. On the other hand, the right channel audio amp board has all new transistors, all new resistors, and all new film and electrolytic caps. Only the diodes, trimpots, and ceramic caps on the right channel board are original.

It looks very impressive and sounds very good overall.

I'll try to post a photo later.
--
Ron Ramirez
Ferdinand, IN
Я этого не понимаю
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#18
It is easy to check with a scope, inject standard signal and se the difference. I bet on resistors. Semiconductors usually do not result in different gain, resistors do, especially those in the feedback loop and the input divider if present. Well, maybe the input DC chopping capacitor.
If it only requires slightl balance adjustment, I wouldn't fret it, after all this is why you have the knob Icon_smile
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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#19
For anyone interested...this has turned into the Marantz that refuses to stay fixed.

First, the left channel started making odd noises when the unit was first turned on that went away after it was on for a few minutes. No magic smoke releases, just a low rumbling through the left speaker that, as I said, went away after a few minutes.

Then...I turned it on a few days ago to find that FM was all but dead...very weak...as if it had no antenna connected (it did).

So...it is back on a shelf collecting dust again. It might remain there for the next five months. Maybe longer. Maybe I'll just cut my losses and sell it as-is to someone who wants to tackle a real tough dog project or use it for parts.
--
Ron Ramirez
Ferdinand, IN
Я этого не понимаю
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#20
Have faith! Icon_smile It's just a transistor sch, they do have higher parts count but are as simple as steamed turnips.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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#21
Mmmmm steamed turnips. Icon_smile
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#22
That's the Russian expression for something that is as simple as it gets.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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