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Scott 340b no right channel

The best way to troubleshoot this would be to input a 1KHz sine wave into the Extra input and go through the unit with an oscilloscope to see where the signal is being lost.
 
Yeah i know but i havnt yet saved up to by an oscilloscope plus ill have lesrn how to use one. Ive been saving up for more trouble shooting and repair gear. I need to find a decent tube tester and scope once i have some extra cash
 
Unfortunately theres not really any techs in my area to helpnwith troubleshooting so im pretty much on my own besides you guys and gals here. Which has definitely gotten me out more than a few jams since i started working on my own gear.
 
Sorry it took me so long to crack this thing back open but looks lile you were right on the 220k resistor. It was completley busted. Going to look through my stash for a replacement now.20210424_151241.jpg
 
No spares in the stash so im going to order a pair jow and just replace both. Thanks for all the help guys! Hopefully ill be reporting back in a few days with a working receiver!
 
Good call, Gadget! Now that we know what to look for, you can just about see that broken resistor peeping out from underneath the black cable in the last photo in post #1.
 
i was honestly not figuring on a broken one, but I've had screen resistors go way off value and cause this kind of thing before. I was figuring on something similar here but a busted one would do it too
 
Alright so my resistors came in the mail today and I decided for good measure I might as well swap both sides since I had a pack of 25 now anyway. After getting them swapped and powering it on I finally was able to get sound from both channels! As an added bonus I can now hook up the speakers the normal way instead of bypassing the phase switch since I cleaned the damn thing 5 times while trying to figure out this dead channel haha. Well thanks again guys! This is now the 6th or 7th full restoration I've completed thanks to help from all you wonderful folks here at audiokarma!
 
Let's see, out of curiosity how many have I finished so far... the first was a fisher 500b, followed by a sansui 1000a, a pilot 240 (the power supply had already been rebuilt on this one but I did everything else), a pair of radio craftsmen c400 monoblocks, a sherwood s8000 III for a friend, and now the scott 340b!
 
Well dang, looks like I spoke too soon! After initial testing and bias monitoring i decided to hook it up to my cornwalls and really test it out. Everything sounded great on the tuner and extra input but when I decided to put a record on and the right channel is still gone on the phono section! I tried all of the different phono hookups on the reciever and although the left side sounds great the right is still dead. Looks like it's back to the drawing board with this one....
 
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well that will be a problem isolated to the phono section. Since both channels work on all other inputs, everything from the source selector to the speakers is fine. Problem is between the phono input and the source selector. Swap the phono tubes first and see if anything changes.
 
Yeah that's the plan when I take it back down tomorrow. The aux input sounds great and I havmt been able to get myself to unhook it yet. I feel like I'm getting so close! Hopefully I'll get it figured out tomorrow
 
Sweet! It ended up being a dead tube. After swapping phono tubes the left side died and right started playing again so I took out the old "Silvertone" tube and replaced it with an RCA from my stash. Shes singing beautifully now and I'm breaking it in with Rage Against The Machines S/t album. Lots of punchy bass with this thing!
 
Haha well the finally fix was easy but man this was probably the most difficult restoration I've done so far. Ran into alot of problems along the way, mostly my fault but luckily its singing now and honestly I feel like I've bonded with it haha. The final steps felt like an ER surgeon telling "Dammit, dont you die on me!!!!" Hahaha
 
having worked on enough "can of worms" things I understand what you mean. Nothing like saying "this has to be the last thing" over and over and over again.
 
gadget73 said:
the tabs aren't critical, just group the connections how they were. Nothing special about it being a square or a circle or whatever if all the sections are the same value and voltage.

can't help on the specific wiring questions, never worked on one of these but if it worked before and you didn't change anything, I doubt thats the problem.

some random thoughts in no special order that may help narrow down the problem area

Usually when I have a dead channel, the first thing I do is swap tubes side to side just to rule that out.

Would be very possible for the speaker switch to be messed up, and wiring around it would easily prove it out. Try it from the 4 to the 16 ohm tap and see what you get.

try messing with the tape monitor switch if you have not. If thats messed up it can cause no signal on one or both channels. Quick and dirty way of taking that out of the picture is to simply run an RCA cable from tape out to tape in. At that point it won't make any difference what the switch is doing or not doing.


Do the output tubes on the non-working channel bias normally? Not sure what the specs are, but you want to see something at the bias test point (pin 5 on the output tubes), ideally something that is basically the same as what you read at the working channel's test point.

If none of that leads anywhere, jumper the two grids of the first tube in the power amp section together. 340b should be pin 2 on V3 and V103. If you get signal on both channels, the problem is before the power amp. If not, you have something going on in the power amp.
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What a fantastic tip for bypassing often-problematic tape monitor switches. That little nugget is a real gem. Many thanks for sharing ✅
 
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