[Ron Ramirez]

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]

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.

[morzh]

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

[Ron Ramirez]

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.

[morzh]

Have faith! It's just a transistor sch, they do have higher parts count but are as simple as steamed turnips.

[BrendaAnnD]

Mmmmm steamed turnips.

[morzh]

That's the Russian expression for something that is as simple as it gets.

[Ron Ramirez]

Nearly a year and a half on...time to resurrect this thread.

I've bought another tuner board (actually two), and another output board. I just finished ordering the electrolytics I will need to rebuild these boards.

I would really like to get this one going again if I can as it looked so good when it was running. We shall see what happens.

Have faith! It's just a transistor sch, they do have higher parts count but are as simple as steamed turnips.

Easy for you to say. This thing has about 57,000 transistors, 86,000 diodes, and a million capacitors and resistors.

Okay, I exaggerate. A bit.

[morzh]

It would have even more were it built around a DSP. A few orders of magnitude more Of course it wouldn't be repairable then.
But measly 57,000 transistors....that's the low end.

[mikethedruid]

I guess I am very lucky. I have an old Marantz SR-4000 receiver-amp I bought new back in about 1979. Aside from having to clean the function switch and pots a few times, I have had to do nothing to it. It just keeps chugging along like the day I bought it. It has always been my main entertainment amplifier, still is. Besides my turntable, I have it hooked up to provide audio from my Blue Ray player and my computer if I watch a movie and want to have great stereo sound. The way I have it connected, I can also use it to convert my vinyl records and old 78s to digital with my computer. Great amplifier. Good luck with yours, Ron.

[Ron Ramirez]

Mike the Druid -

Don't laugh...but I have our living room TV and Blu-ray player hooked up to a Fisher 100-T Coronet tuner/preamp, and that is connected to one of those little Lepai power amps which are sold by Parts Express. Call it a shotgun marriage of tube (100-T) and solid state (Lepai). I don't listen to TV or music loud, so the Lepai serves the purpose just fine and the Bozak Urbans are happy with it.

I really think this 4230 was abused through its lifetime. It was probably cranked regularly. If I can get it going properly, it will never be cranked again as long as it is in my possession.

Mike Morzh -

This 4230 is far more complicated than any of my solid state Fisher receivers. Maybe because it is a 4-channel receiver that can be set for 2-channel operation (which is how I want to use it).

[Ron Ramirez]

Slowly, I've been removing everything from a third power amplifier board which will replace the left channel power amp board.

I finished removing parts Monday evening and began repopulating the board with new transistors and electrolytics last night.

Still have some transistors and electrolytics to go, plus all of the resistors. (I had replaced everything in the right channel power amp board and I want the left channel board to sound the same as the right.)

Very slow work...

[morzh]

Oy Vey.....

[Ron Ramirez]

Oy vey, indeed!

I have installed all of the new electrolytics, all of the new film caps (including a couple 1 uF film caps which replaced 1 uF electrolytics), all but five of the transistors, and all but two of the resistors.

I ran out of 330 ohm resistors. And I also needed three 2SC1327 transistors. Both have been ordered, from the auction site.

I'll install the replacement 1N34A germanium diodes and the two 2SC945 transistors tomorrow. I'll also check the varistor diodes to make sure they are OK.

And then, since I can't do much more with the audio amp board until after the next chemo treatment, I'll turn my attention to the tuner board I bought. I will replace all electrolytics, then install it in the receiver.

[Ron Ramirez]

1N34A diodes installed today, along with some replacement transistors I had forgotten about.

I also began work on the replacement tuner board. Two of its several electrolytics have now been replaced. I probably won't get the tuner board installed in the receiver until after I recover from the next chemo session. And I have to wait for parts for the amp board before I can finish it up.