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Restored CA-1000 Hiss

Everything was working great…cased it up..then, no sound out of the left channel. Back apart and I couldn’t find the issue until I bypassed the filter board. I took the green set of wires to the loudness board and the left channel came back.

Something in the left channel path on the function board is messed up. And the 50 ur old solid wire is showing it’s age, I’ve shave to resolder so many broken wires at the boards.
 
I started to reflow connections then I noticed that the left channel wire had apparently pierced and melted the 2.2nf tantalum cap. The cap still measures 2.2nf but I probably need to order some. I will also reflow everything tomorrow. It’s too late tonight.

I will keep you guys updated…
IMG_4120.jpeg
 
Roger Gorke said:
then I noticed that the left channel wire had apparently pierced and melted the 2.2nf tantalum cap.
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Those look like poly film caps. C540 and 541. 2.2µf/16vdc.

OEM was tant's. Looks like they were swapped out at one time with MKS Wima's possibly.

There is probably nothing wrong with them if they still measure 2.2µf .
 
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Ugh…so frustrating…

Still the same…no left channel. Removed and cleaned all three switches…muting, treble and
Bass cut. Her’s the before and after removal of the switches. I can’t see any traces broken or touching where they shouldn’t.

With the filter board out of the circuit. Both channels work great. And…I do have continuity from the loudness control to the filter board…yellow wires.
 

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"I bypassed the filter board. I took the green set of wires to the loudness board and the left channel came back."

Could you explain exactly what you did. eg, Jumpered from white(L) wire in Green wrap on filter board to white(L) wire in ???? wrap on volumer board.

The green wrap wires go from filter to coupler boards
The yellow wrap wires go from volume to filter boards.
It would make sense to jumper from yellow to green
(apologies, just coming up to speed)
 
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Do the transistors on the left channel of filter board, Tr501, 503, 505, have the right biases as compared to right channel?
Do you have an oscilloscope to sniff around to see what happens to the signal after entering the filter board L-CH?

Edit: change all those 2.2uF caps in the audio path to eliminate any doubts. I’d put audio grade electrolytics just like the OEM. Your call of course. This is a simple board, either one or more Xistors were damaged during muting (the POP) or something physically went bad during handling of the board later.
 
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I don't have much, probably silicon, a scope would be handy (or audio probe).

With unit powered off unplugged you could continuity test between solder blobs marked, low filter switch set to off position, expect less than 5 ohms, this will continuity check the low filter switch.
 

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avionic said:
Pretty slim pickins around here. I'd stay with the Wima's. My 2 cents. :biggrin:
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I know a lot of people use them but for me, every time I use them I clearly lose high frequency response, like suddenly listening from behind a very thin curtain. Then I take them out and get my high notes back. At the end of the day it’s all subjective I understand. I’d change the L-CH ones with something to make sure there are no bad caps in the path anyway. :thumbsup:
 
Think we would all agree this would be a walk in the park if the OP had a scope. It need not be a new item and agree buying a vintage Tektronix is somewhat risky (RIFA...but if you could land a working TEK...) Not a fan of DSO. You can get junk/toy DSO's for about USD20-, yeah a waste of money, but for once in a blue moon use??? Failing that, you could make an audio probe for about USD10-, probably much less depending on spares at hand... Also maybe try tracing audio with a MM? But in the end we are "forced" to troubleshoot without good tools which means, on the balance of probability,,,, Yeah, I'm frustrated
 
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mbz said:
Could you explain exactly what you did. eg, Jumpered from white(L) wire in Green wrap on filter board to white(L) wire in ???? wrap on volumer board.
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The green wires go to the coupler. I connect those to the loudness circuit (where the yellow wires usually attach. THEN, everything works.

Does the filter board do anything other than mute and filter? Maybe a dumb question but at this point, I can live with it bypassed. I don't ever use those switches anyway. Unless I can find a working board. (unlikely)

Yeah, I wish I had a scope and knew how to use one. I am 99.9% sure it has something to do with the low filter switch, looks like it's FUBAR.

FUBAR switch.jpg
 
Roger Gorke said:
I did check the voltages between the two sides and they were pretty close…within a volt.
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Holy mother of god … what happened to that switch? Who did that? You’re looking at your problem right there most probably. If you can get creative and fix that slider clip, I think you’ll solve your issue. In the worst case, maybe you can bypass that switch alone?
 
mbz said:
Yeah, I'm frustrated
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Me too!!!

mbz said:
Think we would all agree this would be a walk in the park if the OP had a scope. It need not be a new item and agree buying a vintage Tektronix is somewhat risky (RIFA...but if you could land a working TEK...) Not a fan of DSO. You can get junk/toy DSO's for about USD20-, yeah a waste of money, but for once in a blue moon use??? Failing that, you could make an audio probe for about USD10-, probably much less depending on spares at hand... Also maybe try tracing audio with a MM?
Click to expand...
Is there a schematic or diagram for an "audio probe?" I thought about tracing the audio (AC) with a MM. Is that the/a correct way of tracing audio?

What are some good, reasonably priced new scopes? I looked on FB marketplace and found a Tek TDS320 for $200, a Tek 2235 for $160, a couple of BK scopes, and an LG OS-5020.

And finally, last night I again bypassed the filter board and the amp sounded fantastic. A razor sharp center image (Norah Jones) through some Dynaco A-25s.
 
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