Sansui SM-320m
- Thread starter mark long
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Just remove all tubes and use DBT on first run...
Mike244
Active Member
mark long
Active Member
i tried a replacement on this tube already. no output on any source or tuner. Power is functional, dim bulb 12/15/40w bulbs all light up like Christmas with tubes inserted, power is stable with them all removed. removing 1 tube at a time with dim bulb doesnt reveal the source of the issue. Tome switch crackling between mono chan 1/2. detoxit did not improve the situation. these are 6ohm 6w speakers. replaced all tubes with known working ones, no change in behavior. Dim bulb is pegged immediatley. Could be bad filter caps, IDK. Pretty depressing as these non-pcb receivers are like freddy kruger ripped up my soul.
Oof. A rats nest comparable to the AU-70 integrated in there. I know it's no fun redoing point to point work like that. That said, you have an excellent example of a very rare receiver there. Certainly worth getting up and running again. I'm struck by his clean the inside of the unit is, usually these are loaded with dust and the steel chassis is all discolored from age. Must've been properly stored, or at least kept covered, for a long time.
Mike244
Active Member
Are you have multimeter or tester? Can you check AC on secondary power trafo winding ? Can you check DC after rectifier? on main caps, on B+ output transformer? Tube amps easy to fixing - you just need going step by step....
And of course - remember safety rules - this baby have dangerous voltage inside!!!!!
And of course - remember safety rules - this baby have dangerous voltage inside!!!!!
mark long
Active Member
i have a meter and a in-circuit capacitor tester. there are cracks on the underside of each main filter cap. ill start by testing those. Though I'll be honest and say this may end up on a bench for repair by someone with the correct tools. Also, just curious, the yellowing on the frame..is that heat treating or age?Are you have multimeter or tester? Can you check AC on secondary power trafo winding ? Can you check DC after rectifier? on main caps, on B+ output transformer? Tube amps easy to fixing - you just need going step by step....
And of course - remember safety rules - this baby have dangerous voltage inside!!!!!
Mike, it sounds like you know your stuff on these old rigs, can you point out the winding you would like a measurement from? The schematic is microscopic.
mark long
Active Member
SM-320M / Serial: UL780
mark long
Active Member
so the repair folks called me today and said the am/fm tuner is dead and not fixable...they said the copper coil for the tuner is broken and its not fixable because its "hair size". I have no idea where this coil is so i asked them to send me a picture of this bad component. again this is confusing to me because doesnt this receiver have two separate tuners thus two separate coils? I'm not happy since i've invested quite a bit of money in this repair. anyone know if this is something i can repair or replace myself? I have a 120x camera microscope so i intend to take a closer look at this issue when i get it back. RIght now it will require an external tuner but the aux inputs should work fine and output audio...however this being the first of the multiplex receivers means this restore is basically a dud.
Ouch. I've had a couple of cases (not in hifi equipment) where inductor coils came off a board, breaking off the coil lead wires. In both cases there was just barely enough to solder on new tails with additional coil wire and remount them. One was on a 3 kW broadcast studio UPS I still use here. The other was on a big ass linear power supply I repurposed for running some specialized computer gear.
Not sure if a repair of the coil you have is feasible, or if a suitable substitute could be found/made. Please post an update once you've put it under the scope.
Not sure if a repair of the coil you have is feasible, or if a suitable substitute could be found/made. Please post an update once you've put it under the scope.
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mark long
Active Member
they said i can either pay for the repairs for getting the aux input working or remove their repairs and send it back minus return shipping. I'm opting to pay the return shipping and having them "revert" their fixes for the PS and Amp. Not worth investing any more money into this receiver if the AM/FM is bad. Once I get it back I'll take a look at the coils they said are bad.
Not every investment turns out to be a winner but the smart move is to know when to move on I guess. We're talking over 800$ in labor/parts, not going to happen for what is basically a tube amp at this point. And I think their offer is fair considering I paid for a diagnostic with the assumption they can fix any issues that arised, regardless of part requirements...obviously they couldn't meet that promise and gave me the option to bail. Id say they will likely rethink agreeing to fix these really old receivers in the future after this..
Not every investment turns out to be a winner but the smart move is to know when to move on I guess. We're talking over 800$ in labor/parts, not going to happen for what is basically a tube amp at this point. And I think their offer is fair considering I paid for a diagnostic with the assumption they can fix any issues that arised, regardless of part requirements...obviously they couldn't meet that promise and gave me the option to bail. Id say they will likely rethink agreeing to fix these really old receivers in the future after this..
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Damn. At least they gave you an out to minimize the $ hit. I'm a bit surprised they didn't first get the power supply sorted enough so they could test the tuner, then move on to the output stage once it was known the tuner was functional. That's how I'd approach it, but then I'm not a professional tech, so maybe that wasn't a practical approach.
Kind of a shame, as is the likelihood they will now turn down taking on future work on gear like this. There is already a dearth of decent techs versus demand, so good ones getting burned and shying away from complex repairs is a real loss.
Kind of a shame, as is the likelihood they will now turn down taking on future work on gear like this. There is already a dearth of decent techs versus demand, so good ones getting burned and shying away from complex repairs is a real loss.
mark long
Active Member
the only schematic on the internet practically is mine, and that's plastered under the hood of the case. I did lookup a 67 sansui 3000 and it has a 455kc if. but as you said it's hard to know for sure for this one.
https://audio-circuit.dk/downloads/sansui1/Sansui-3000-rec-sm.pdf
i'll have to pull it when it arrives and examine. https://ibb.co/MMN8gPR
https://audio-circuit.dk/downloads/sansui1/Sansui-3000-rec-sm.pdf
i'll have to pull it when it arrives and examine. https://ibb.co/MMN8gPR
