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800C Volume Pot problem.

In Larry's case, he measured non-linear tracking of the volpot, didn't he?
In Bryantenn's case, he should measure both volume pots and the balance pot to see where the root of the problem lies.
I've used the balance pot at as extreme as the 3:00 position to even out problems that were either the volpot or the balpot. As long as the stereo image is centered, I've been Ok with it.

Measure at: Just on, 10:00 position, 12:00 position, 2:00 position. Usually, the volpot non-linearity affects the resistances at the 8:00, 9:00, and 10:00 positions.
 
Hey Don, even if someone gave me the right parts, it would still be over my head. :sigh:

I can detect no wiper motion on either the master or balance pots.
On/Off is the only thing verified with my meter.


Steve


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Thanks Don. :thmbsp:

:dammit::grumpy:

This is why I'm never going to update my 500C. Too much **** to deal with.
 
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Westy56 said:
Thanks Don. :thmbsp:

:dammit::grumpy:

This is why I'm never going to update my 500C. Too much **** to deal with.
Click to expand...

Post 16 lists the discrepancy. Defiantely a Volume control problem. Ideally there should be no more than a few ohms difference.

You think a 500C is BAD??? Take a look at this. 1/2 the depth in the chassis, 1" wider and same depth as an 800C. Sansui 1000A. I got it in NON WORKING Order. Recap and some tubes, and it's runnign. I did this one 2 years ago. This was my Cherry popper. It's still kickin ass and takin names.

BEFORE:
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After:
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I've since added a variation of the 4 pot mod, and two of the can's have been replaced instead of stuffed.

Larry
 
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Fishers are comparatively easy. The resistors rarely drift. Most work 45-60 years after the original manufacturing date - often with the original tubes.
They exhibit the following problems:
1. Aging power supplies.
2. Aging non-power supply related electrolytic caps
3. Coupling caps need replacing
4. Volume pot and balance pot issues
5. Dial string breaks occasionally.

But they don't have:
1. circuit drift due to resistor value drift
2. problems with the tuner circuitry unless it's been messed with
3. fire hazard problems
4. variations in sonic quality - You restore it and it'll be good - pretty much guaranteed.
5.Many almost impossible to get to spots
6. Lettering that wears off from a careful attempt at cleaning - either on the dial glass or the faceplate
7. shelf-queen-itis.

Just like any mechanical device, ones of this type have mechanical problems typical across the breed. Got a classic car? Talked to other classic car owners? Then you know what I mean.
 
audiodon said:
Steve,
Look where the wires go on the volpot. Those are your test points.
Click to expand...

Unfortunately, the ends of the wires to the vol. and balance are hidden inside somewhere.
The only exposed ones are for power.

:sigh:

The knob on the right is for balance. With the vol. set where it is in pic, I have channel balance.
As I turn up the vol. the balance control has to be moved closer to 12:00 to achieve balance.


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Steve

It is a volume control situation. If I turn on the loudness, the imbalance gets better immediately.
It is still way off, but confirms where the problem is.....I think. :scratch2:
 
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You know that that center channel/balance knob is two knobs tied together using a split shaft and each is separate from the other, correct? You're moving the balance part separately from the center channel part, right?

I'd look to cleaning the loudness switch first. It could have a dirty off position or be loose in its retainer clips. Clean the leads on that loudness button with a non-lubricating electronic spray cleaner. Sometimes you can just press on those metal retainers if the switch feels loose to your hand to tighten the contacts a tad. Try the unit after doing that before digging deeper into the unit.

To test your volpot, rest the unit upside down and remove the bottom chassis cover.
Pull off the volume knob, use a socket to undo the lock nut on the front and pull the volume control back into the chassis. Then you can access the wires.

The wires are in the mostly sealed back part. the farthest back part is the switch. The two in front of it that look the same and probably have three leads on each side are the volume pot pieces. Also, spray it into the two potentiometers on the volume knob and work it all the way from almost off to all the way on about 30 times or so.
 
audiodon said:
You know that that center channel/balance knob is two knobs tied together using a split shaft and each is separate from the other, correct?:yes: You're moving the balance part separately from the center channel part, right?:yes:

I'd look to cleaning the loudness switch first. It could have a dirty off position or be loose in its retainer clips. Clean the leads on that loudness button with a non-lubricating electronic spray cleaner. Sometimes you can just press on those metal retainers if the switch feels loose to your hand to tighten the contacts a tad. Try the unit after doing that before digging deeper into the unit.

To test your volpot, rest the unit upside down and remove the bottom chassis cover.
Pull off the volume knob, use a socket to undo the lock nut on the front and pull the volume control back into the chassis. Then you can access the wires.

The wires are in the mostly sealed back part. the farthest back part is the switch. The two in front of it that look the same and probably have three leads on each side are the volume pot pieces. Also, spray it into the two potentiometers on the volume knob and work it all the way from almost off to all the way on about 30 times or so.
Click to expand...

I'll pull the one on the other unit and test it. Maybe I'll be able to do the fix in circuit on my main one.

Everything this preamp touches turns to gold. For the first time my ST-70 sounds wonderful.
Up until now, this thing has only been used as my tuner. :dammit::withstpd:

Steve
 
I got the pot (saturday) from Don. Thank you Sir!!!!!!!!!. Pot is exact replacement. It's off by a few K but nowhere as severe as the original. I'll put it in 1st thing in the morning.

Larry
 
larryderouin said:
I got the pot (saturday) from Don. Thank you Sir!!!!!!!!!. Pot is exact replacement. It's off by a few K but nowhere as severe as the original. I'll put it in 1st thing in the morning.

Larry
Click to expand...

Good luck Larry.

Will you post a picture of the old pot when you remove it?


Steve
 
I put the new one in. It now has the left channel lower than the right. Balance is about 10:00 to balance it out. I oHmed out the pots before installing and the imbalance was about what Don had written. So now I have 2 pots, one right side dominant and the other leftside dominant. Time for some surgery after Son's wedding this afternoon. Plan on mapping out the resistive pads and taking the 2 closest matching and putting them in a pot case. I've gotten so I can take them apart and put together in my sleep, with my eye's closed. But they work better when I'm awake and have my eye's open. :D

The pots in the 800C - 500C- 400 are the same. But they are physically different than the X-202. I'll post a pic later.


Larry
 
Larry,
Tubes came yesterday and worked out fine.
Sorry the pot wasn't a slam dunk. I'll be interested to find out if combining the two does something for you. I didn't think the resistance variation was very high at all pot to pot.
 
Agree with your assessment. It shouldn't sound that unbalanced. Gonna map out all 4 wafers, plus the two in the short shaft Ambassador pot I have (Same as the 800C pot but with a shorter shaft). See if I can get two that are so close it's ridiculous. Then put them in the casings and go for it.

Larry
 
Hi Larry,
Hope that rebuild of the pots works out for you, it get's pretty annoying when
these pot have balance control issues.

Tube
 
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I got the 2 closest wafers installed about 2 days later. Sllight imbalance, but it's better than it was. Sometimes I wish there was an alps WITH A SWITCH on the back that would work. I refuse to "butcher"(my opinion) a perfectly good looking unit to install a power switch somewhere it wasn't designed to go unless it's the only choice I have left.

Welcome to the club Keith. I don't expect an unrestored 40 year old car to perform as original from the factory, why expect that from a piece of audio gear. Learn to live with it's idiosyncracies.

Larry
 
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