Sansui 400...

I got this 60s receiver a few weeks ago at a radio show to work on and learn some SS repairs also...
Note on it said one channel was working,, and FM worked,,, I got a copy of the service manual and got both channels working with transistors and PS caps I had,,, I am waiting for permanent transistor subs from Digi,,,

The good,, the AUX input works fine with a CDP,,, AM works fine, FM works OK, but needs some attention... Bulbs work,, dial fuse lamps need replacing...

The bad so far,,,
1... FM works OK and comes in strong,,, tuning meter works, but orange lamp for tuning indicator only lights when FM is first selected and stations are dialed in... It only lasts 10-15 seconds then dims off, and won't come back on until AM or another selection is used a while, and then FM tried again...
Not sure if MPX stereo is working while light is on, as it isn't on long enough to listen,, It only last 10-15 seconds then dims off, and wont come back on until seems as if something inte ckt is going out of value/overheating??

2... I have measured Voltages at all the transistors on MPX and indicator boards, and can post the results...

3... Tuning meter doesn't move at all in AM...

I have a little experience with SS,, but not much with tuners, MPX and indicator boards,, so that's where I'm stuck now!!! I posted the service manual hoping to get some interest/help, as this old receiver really sounds good so far, and deserves another chance!!! I have a Sansui 800 to compare it to..

Thanks in advance!!!
 

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Nice vintage..


I wouldn't be surprised the tuner needs calibration. If you have the tools and measuring equipment you could try, the procedure is in the manual. Otherwise, find a tech who can do it, never start turning the post and coils at random.
 
Don't want to be intrusief and I understand this is a learning project but I wonder why you would swap the good transistors with replacements. They were chosen for a reason :)
"Intrusive" Didn't replace any good transistors,,, the ones I replaced had leads broken/corroded off... 2sc536s,, 2sc538s, 2sc458s,, Replaced with 2n3904s and 2n2222s I had on hand, to get it working... Waiting on Digi order as we speak.
 
I suspected TR503 yesterday,, took these readings with ohmmeter and a little components tester, but couldn't get any one to confirm them...
Still need to trace AM meter ckt... I can't access the lug on the switch yet...
Thanks for the assistance!
 

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Thanks much,, yep I took it out, tested and replaced it just to not lose it!!! I asked yesterday but got no responses! Do you think it's the indicator bulb problem? I looked for those(2SB54) and not sure if they real or not,,, prices are all over place...

I read it can be subbed with a 2N3906,, but the ckt would need to be modified,, I don't want to do that, trying to keep it as close as I can with reasonable parts... I have an old Fisher 220T I went thru maybe 10 years ago, with a lot of support, just needed the preamp board rebuilt, but it was easier to access than this one,,, may have been a year or so earlier also,,,

Yep,, this Sui dates to 1967 IIRC,, Ge was still used then I guess...

I'll continue tracing the AM meter problem also, while I look for a solution to this transistor,,, and keep posting progress and questions!
Thanks again for the help!!!
 
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Germanium's biggest flaw was leakage. Silicium's have build-in diapers. ;)
2N3906 is definitely not a sub.

Many 2SBxx can be substituted with AC151 as drop-in replacements, so if you find some, buy a few.
Original #s are best but hey, they're rare.
https://www.electro-andijk.nl/index...ronica/transistors/ac/ac151-transistor-detail
https://www.electronicparts-outlet.com/nl/2sb-series/2741-2sb54.html
Other subs could be 2N2431, 2N408.

Here is a nice asset to find subs: https://www.google.com/url?sa=t&rct...ivalents.pdf&usg=AOvVaw1gkOT3AMPbXAd9DBzF2_ZT

Also, siliciums measure +/- 0.6-0.7V across the diodes, germaniums more like 0.2V

Now that we know that germaniums are all over the place in this amp, the meter problem could also be related to them leaking.
 
Hi Netlist,,,
Thanks again for the info,,,
Well I read about the using 2N3906s somewhere on here with schematics and diagrams,,, but I don't think it was a good idea so I didn't save it,,,

That sub book you sent would be nice to have ,,, Like an RCA tube manual for transistors!!!

I'm not ruling out anything til I find the problem,,, Ge trans may be trouble,,, but they sound more like tubes than Si,,,

I think the AM meter problem is going to be harder to track down,, I spent an hour trying to access the switch to trace the meter wires, and inspect the wafers/contacts,,, but I just can't see it, and removing the switch isn't an option... The FM has another PCB between the meter and switch,,, AM is just switch contacts to meter,,, it shouldn't be this hard to fix!!!!

I think replacing 2sc54 with the same number will be best, but they aren't cheap + shipping,,, I think I'll continue working on the meter and indicator lamp problem, until the Digi order gets here,,, then replace the temporary transistors I used to get the amp going with match pairs, and look in to replacing small capacitors,,, If that all goes well,,, I'll order a 2SC54 for the FM meter...
Not planning on giving up!!
 
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