low volume in left channel SANSUI 600L

[tarmacrar]

hello

i have a problem in the left channel of my sansui 600l

when i select FM radio the left channel is weak (volume lower) than right channel !!??
when i activate the mono button i get the sound ok right and left (same level)

this problem is in FM radio (i cant check AM because i don't have any reception where i live )
same with PHONO IN
but in AUX IN everything work fine in stereo and mono ???

i have tried an other set of speakers i have cleaned the pots and selectors
problem persists

any guidance, help I'll be thankfull

 

[bolero]

I believe the FM tuner uses the phono preamp circuit, minus the RIAA section in the 600L. So that narrows it down to the phono preamp?

Did you gain match the transistors you replaced, between LR channels?

I suppose it may possibly be the switch contacts. Doublecheck your soldering work, look for cold joints?

Good luck!

 

[tarmacrar]

hi bolero
you mean hfe ? all the transistors are identical hfe 480 ~
please correct me if iam wrong

 

[bolero]

Yeah, it's good to measure the actual parts though & match them as close as possible. From what I've researched. Although I think some circuit designs aren't so critical?

It may just be a bad solder joint. If you trace the signal & compare L/R it might find the culprit

 

[tarmacrar]

yeah but in aux every things work fine ??? crazy radio

 

[bolero]

Exactly: that means the problem is somewhere in the phono section. Aux is a different area of the circuitboard

 

[tarmacrar]

ok can you please show me where is the phono section ?

transistors that i have changed are TR 601-602-603-604 and TR701-702-703-704

 

[bolero]

TR 60x is phono section

TR 70x is line/aux section

 

[bolero]

I just thought of something: VR 601 is the FM balance adjustment. I don't think that would affect the phono LR balance though?

 

[tarmacrar]

so i have checked all those transistors all seems to be ok solder is ok

im lost

 

[tarmacrar]

it's the MPX separation in the (block diagram) i never touch it

 

[bolero]

Ps I wouldn't start messing with the actual tuner: it's probably nothing to do with tuner alignment, since the phono signal is affected too. And you don't want to get into that mess

 

[tarmacrar]

yes i agree with you

i don't know what else i have to check ...

 

[bolero]

Did you recap it too?

I think you need to start measuring signal & comparing L to R to find where it's getting lower

 

[tarmacrar]

no i did not recap it
all what i have done is the transistors replacement

 

[tarmacrar]

ok i found the culprit
as bolero said the problem was in the phono section

I believe the FM tuner uses the phono preamp circuit, minus the RIAA section in the 600L. So that narrows it down to the phono preamp?

Did you gain match the transistors you replaced, between LR channels?

I suppose it may possibly be the switch contacts. Doublecheck your soldering work, look for cold joints?

Good luck!

due to oxidation / dirt / invisible layer of insolent in the base leg of the transistor TR601 the solder is present , so visibly is soldered but no strong electric conductivity...
whats made me crazy is that when i switched on the receiver the first time after i replaced those transistors it's work fine for more than 2 hours ... i think is when i switched off the receiver and the transistor get cold the solder and the leg recontract witch lead to that bad conductivity... this is the result of my investigation...

after this experience i highly recommended my self and everyone's to clean the legs of any part they want to solder with isopropyl or any alcohol before soldering even if the part is NEW to avoid as much as possible this kind of bad surprise

Thank you very much bolero you helped me a lot and I was really pleased to have your help
thank again

 

[bolero]

Good news!!

Congrats, glad I could help