Sansui 661 Idle Current Issue After Recap

[T Somerville]

Your outputs aren’t the trouble I’d start with replacing the 2sa726 if you still have static next step is to isolate if the noise is from the pre amp section or output section to track it down noise is normally a transistor failure or bad joint.

If idle current isn’t stable with new trimmers it’s possible the driver transistors are not matched or one is leaking and should be changed however first try isolate the noise issue

Will replace those transistors tonight. How do I go about isolating the noise from the pre amp? There is no pre/main option for this receiver and I dont have a scope.
I think I have some bourns trimmers on hand to swap out. Will get back to you when works complete.

 

[quadmatrix82]

Will replace those transistors tonight. How do I go about isolating the noise from the pre amp? There is no pre/main option for this receiver and I dont have a scope.
I think I have some bourns trimmers on hand to swap out. Will get back to you when works complete.

Ah I hadn’t looked at one of these in a while and assumed it had the pre main outputs on the rear that makes that test a little more difficult but not impossible

Try the transistors first and make sure your meter is ok and the fuse as Hyperion suggested maybe leave the trimmers for now and just use contact cleaner to clean your existing ones

Unstable current suggests the bias transistor is faulty or some other transistors you replaced or remaining are not matched when they need to be as Hyperion suggested hope that helps

 

[T Somerville]

You say you replaced maybe 4 transistors in the pre-amp, what was the type number of the originals? 2SC1313 ? (as per the schematic). If it was, you know that KSC1845 has a different pinout? 2SC1313 = BCE from left to right (legs down) flat face towards you, whereas KSC1845 = ECB under the same conditions. So you would have to install the replacements the opposite way round from the originals for them to be correct.

BTW there are 4 transistors in the Phono/EQ amp, and 2 in the pre-amp - all are 2SC1313 according to the schematic.

It has been suggested to replace some 2SA726, with KSA992 which is fine, (TR01,03 & TR02,04?) however, did you know they need to be (Hfe) gain matched pairs?

Finally, there is a question mark about your DMM, it is possible that you may have blown the current range fuse, which obviously affects the operation of the current ranges, and with some meters affects the voltage ranges as well. So I think you need to verify correct operation of your DMM as a priority, before proceeding.

So im looking at the boards now and confirming the pre amp transistor originals were 2sc 1222 replaced with ksc 1845. Pin outs are the same. There was 6 in total.

The 2sa 726 on driver board were replaced with ksa 992 fta. When testing with the Atlas Peak the 2sa 726 hfe was 375 and the ksa 992 hfe was 475.
Is that close enough to be hfe matched?

Driver board replacement transistor pin outs confirmed to be correct.

Confirming the DMM works and the (1) fault code is when the reading is out of range. Thats concerning if the idle current is way to high for it to be red on 200ma setting