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I strayed, maybe someone can help.

Richs_Trains

Richs_Trains

Well-Known Member
Okay, so I have a ton of Marantz stuff, I love it, but every now and then I stray. This tine it is an Optonica SM 3205 amp. Optonica was Sharp's attempt to compete with the big boys in the 70's. I have a 4646 and it is built like a tank with three power supplies (one for each amp and one for the pre-amp), so I thought I would take a chance on this one I only spent $37.50 for it, so if it's a fail, that's okay. I hooked it up on a DBT just to be safe and it passes, but there is no audio from any source. This is probably beyond me, but I thought somone might have worked on these before and would like to see if it will run again. Any help or info (can't find an SM for this one either) Thanks as always Rich

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Best to check the Dc offset at the speaker terminals to see if you're getting anything. Then get some additional fuses to replace the two that are visible and any others we don't see in your pics. Looks like the left one is marked 1A 125v and the other is 4A 125V. Keep the DBT in though to protect against more damage.
 
Left channel 13.1mv / right channel 10.5mv. Went ahead and re-capped because it was so accessible I now have very low volume on both channels. I have de-oxit all controls and switches and the headphone jack.

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Unfortunately, no, my tech said to put signal into the 'record out jacks' and that would bypass the pre amp, but wouldn't it be at full volume then? I did find a hardcopy of the SM, $20, should have it Wed. Thanks all, I know this isn't a Marantz, but I hate to see any classic go to the recycle bin. Rich
 
how about headphone volume... make sure to check grounds by doing voltage drop test at the actual ground pins and chassis, or transformer center tap. the amps adjust, so im guessing its a delivery problem or pre amp failure, but im only going by how a marantz flows. start by tapping in a set of headphones right to the amp output on the board, with also removing the wire to eliminate any speaker output delivery shorts.
 
check the fuses ..
maybe try touching the coupling caps briefly to main amp to see if test speakers hum .
 
I just don't have headphones right now, but guess they are kinda helpful in diagnosing problems, so I'm going to get some today. Thanks Rich
 
Hope you enjoyed the weather Airtime! Got headphones, same condition on headphones, volume very low, have to turn up to 3/4 just to hear it. Controls function, but volume is non-existent. Thanks Rich
 
Well than it's time to start tracing. You can use a DMM to trace a signal. Any signal like a CD will do. Start at the input jack and trace it to the first board or connection and see at what point the signal drops out or stops being amplified. I would say measure the PS voltages and maybe you'll get lucky and see if something dropped out? But without a schematic, for me anyway, it's just guess work doing that.

I usually cheat and just go to the volume pot itself. It can give you a quick idea if anything is getting up that far. It should be more of a signal that at the input point. Unless you are dealing with a passive front end. Check the any switch that controls speakers, muting, that kind of stuff first as well.

If it's both channels it's either a power issue or come control that crapped out; Also check the output transistors if there is any voltage on the legs of those things. Those are Darlington packs (of shorts?) and you are going to have to cross reference that number to a replacement to find an available data sheet.

Yeah it's cooling down here. Hitting the mid to low 90's. Good hiking weather!!
 
It is both channels and they are Darlingtons, I have found some, but don't know if they are fake. I have the SM coming 'snail mail' this week. I don't usually get units other than Marantz, but I have an SM-4646 and it is a very nice unit, so I took a chance on this one for $35.00. The build on this one is nice also. Couple of really nice features ... the bottom has a large access panel which exposes the complete underside of the PC board, BOTH sides of the board are silkscreened with the component orientation and designation, positive and negative terminals are represented both with a + symbol on the + side and a 'white half moon' on the negative side, and whether it is good or bad design, I liked having everything on one PC board that was completely accessible from both sides. I hope we can get it going, I will try to scan and post the SM when I get it. Thanks all for your help. Rich
 
I have an Optonica SM-1515 with one channel out. I eliminated the Darlingtons as the issue by switching them as well as the predrivers with no luck. I am going to check back to see where your problem was and see if it might apply to mine.

These Optonicas are sure well built and look good with the fluted knobs. I am anxious to see if they sound good as well.
 
One time I had my hands on a Optonica receiver. Built quality and the sound was excellent. I mean real good!

Did you start tracing out were the signal drops out
 
I have not started yet, according to tracking the SM is half way here. Should have it by the end of the week and then I'll go back to the Optonica. I hope we can bring it back. Rich
 
Guess I need to wait for the SM, tried to replace the burnt out meter lights using some bi-pin marantz lights. Must be wrong voltage, they are quite dim. :(
 
Ok, the manual came today and it is for the wrong model :(, so now I have to argue with the seller. Hopefully the right one will be here soon!
 
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