Fisher 100-T balance question

ronton3

ronton3
I have a restored 100-T preamp/tuner(caps, orange drops,solens, LCR, bridge rectifier, all power supply caps). everything works and it sounds great, the issue is the balance control. It will come into balance(I use the Sheffield XLO cd for testing), but the control must be turned to the right(Max B) almost to the 3 position. I would like for it to be in balance straight up. I have tried different 12 AX7s in the V-16 output amp position. Any ideas where I should look. Thanks ron
 
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Try the CD again with the cables reversed (L to R, and R to L)to rule out a imbalance in the CD PLAYER. If the balance offset is same with the cables reversed it's in the 100-T. Is the imbalance in all positions on the selector?? Have you DeOxit'ed the pots and switches???

Larry
 
Tests

Switching cables has no effect, if I use the switch to reverse the channels left and right change, but the level is still the same before the change(louder on the left side) and I still have to turn the control to the right to bring it in balance. FM is the same, but seems the right side is even worse. I rarely use the tuner portion, stations tune great, but there is whistling between channels. The deoxiting was done about 7 or 8 years ago when it was first restored, or at least I think it was. Thanks ron
 
Balance is before volume, but immediately before the balance is the channel switch (Norm/Rev) and the Hi and Lo Filter Switches. If it's been a couple of years or more since last DeOxit, it's a good time to go ahead and do them ALL again. (Sometimes it takes more than 1 application, especially on older gear) Swap V14 and V15 (Tone Control amp tubes) and see if you've got a weak tube (possible). Also swap V12-13.

Do you have a tube tester or access to one? If so Check all the 12ax7's. There are 2 phono amp, 2 tone control, and 1 output. V12-13 (phono), V14-15(Tone Control) and V16 (Final amps). I don't think V16 is the problem. More like V13 or V15 might be weak. FM on the right goes thru V13 and then V15 and then V16. Same as Aux. So the whole chain needs to be looked at.

Larry
 
Deoxit in progress

Thank you for the detailed instructions. Deoxiting and ProGold lubricating are in progress, I am doing the X202 at the same time. I have a 752 Hickok in working order and will report back after the swapping and testing. Thanks ron
 
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Another issue, may be related

The deoxiting was helpful in a general way but did not solve the balance problem, switching tubes and checking FM and AUX, got confusing so I am going to test. In the meantime the second side of the cap shown in the second pic was never soldered and I am not certain just where it goes, any advice would be welcome. Thanks ron
 

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I have one with the same issue...
mine had a cap can replaced and the MPX board realigned...
But to have the stereo signal balanced the indicator has to
be turned to 3 O'clock. On the scope the signal is the same
from both channels....

I am curious to see if a remedy(other than rotating the pot) can be found...:lurk:
 
Looks like thats the "safety cap" or as some call it "death cap" It keeps the voltage on the chassis on a non grounded unit to a safe level. I think it connects either at the fuse or n the UNSWITCHED Outlet. Let me see if I can find the schematic and I'll let yoou know for sure.
 
Bingo. Found it. It's C-118 as noted in the schematic drawing.
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Wow neat arrow

I don't know how you did it, but that arrow pointing to the fuse holder is such a neat thing. I thought it was 118 or 119 but wasn't certain where to put it. I now know that f1 stands for fuse, thanks for the lesson and help. Last night it got confusing trying to substitute and find the weak tube. This morning I took 2 matched 12AX7s' from a X100 and placed them in V14 & V15,no change. I placed them in V12 & V13 and proper balance was restored. So it was one of those two, and I will use the tester to determine which tube, but I won't know which place it was in. FM still seemed off some so I switched places with the 6AQ8s at the back and that seems to have helped there although I don't know why. Many thanks ron
 
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