Loud hum through speakers - Yamaha CA-1000

I've done a bit more work:

I replaced all the capacitors on the power supply board. The hum is still there, but is quieter. It got quieter when I replaced the four larger caps (C705-708). However, I put back in the original four and it was still quieter. I know that's weird. Since the large caps on the electrolytic board are rather expensive, I can't justify replacing them as a guess right now. Especially when it seems more like a grounding issue.

I'm really having trouble finding any potential pinched, broken, etc. wires or problematic solder connections. Any tips?
 
How about the two largest caps..
Just for shits and giggles- by-pass the coupler switch with a patch cord pre-out to main-in
 
I've done a bit more work:

I replaced all the capacitors on the power supply board. The hum is still there, but is quieter. It got quieter when I replaced the four larger caps (C705-708). However, I put back in the original four and it was still quieter. I know that's weird. Since the large caps on the electrolytic board are rather expensive, I can't justify replacing them as a guess right now. Especially when it seems more like a grounding issue.

I'm really having trouble finding any potential pinched, broken, etc. wires or problematic solder connections. Any tips?

It could also be a bad cap in the power supply,can't rule it out.Look at the bottom side of the two large caps for signs of possible venting.
 
Verify all these ground lines read continuity from the "star ground" to there various destinations as well as "chassis ground". Including the various lines marked E,ES and EM.
 

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I'll do my very best checking the ground lines but I'm quite a novice at reading schematics. I can't figure out where the "star ground" is on the actual board. Are you able to mark where it is on the attached image?
 

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Are there screws on the circuit board. A lot of times those will be loose enough to cause a ground problem. One time when I was working on an amp I had the bottom panel off,fired it up it hummed like He11. Finally figured out that it did not like my carpet covered steel bench. When i tipped it on it's side hum went away.
 
Thanks for the info avionic. I won't be able to get to it for a few days but will post back once I do.

Are there screws on the circuit board. A lot of times those will be loose enough to cause a ground problem. One time when I was working on an amp I had the bottom panel off,fired it up it hummed like He11. Finally figured out that it did not like my carpet covered steel bench. When i tipped it on it's side hum went away.

I'll have another look around to see if I haven't tightened something properly.
 
I've finally taken the time to test the "star ground" and "chassis ground" at all the various points and everything seems fine. I also reflowed the solder on the two big caps (which have bypass caps) and no change.

Any other ideas?

If not, and I can't find a good local tech, I might want to send it to you avionic if you're available. What is a guesstimated turnaround time right now?
 
I recently aquired a Kenwood KA-7100. So I switched off the coupler on the CA-1000 and attached the preout jacks to the AUX input of the KA-7100.

There was a very faint hum in the speakers. It is probably 3X quieter than when the speakers are connected directly to the CA1000. I'm not sure if it was 120hz but it was definitely higher than 60hz.

However, while the volume knob on the CA1000 did affect the volume of the music, it didn't affect the volume of the hum. (The KA7100 produces no hum itself into the speakers.)

Does this give any clues? To recap some pertinent information from previous posts—when the CA1000 is directly connected to speakers, and when the coupler is on the CA1000 produces a very audible 120hz hum into the speakers, when the coupler is off it produces a quieter 60hz hum (but still louder than when it was connected to the KA7100).

Thanks.
 
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Revising an old thread


Tracing/testing ground wires.
Amp powered off/unplugged

Remove metal shields on function and tone boards.

Check Function board GND track from from phono 1 & 2 inputs (P1&P2
on trackwork) No burnt track.

RED multimeter probe connected to PHONO GND connection.
In turn, measure resistance at each of the following points
Note, test at solder joint/blob or metal tab not at bare wire

Function Board, white outer wrap, middle (clear insulated) wire
Function B, orange wrap, middle (clear) wire
Function B, brown wrap, middle (clear) wire
Function B, red wrap, middle (clear) wire
Volume B, orange wrap, middle (clear) wire
Volume B, brown wrap, middle (clear) wire
Volume B, red wrap, middle (clear) wire
Volume B, yellow wrap, middle (clear) wire
Electrolytic B, tab/pin EM
Electrolytic B, tab/pin ES (2 pins, test each)
Electrolytic B, tab/pin E (4 pins, test each)
Speaker A, Black speaker post Left then repeat for right
Left Power amp, black wire, pin "E" repeat for right power amp
Left Power amp, black wire, pin "e" repeat for right power amp
AUX-1 RCA connector, outer, either L or R channel
PRE-OUT RCA connector, outer, either L or R channel
Power supply/relay board, solder blob E

Expect 1-2 ohms, the measurements at the RCAs may be higher
due to oxidation.

I assume you don't have an oscilloscope, maybe an audio probe
would be helpful/more on that later
 
Thanks so much for visiting this thread mbz and for your suggestions! I have the CA1000 out and ready to test and will start as soon as I can. I’ll report back.

I don’t have an oscilloscope or audio probe.
 
Ok...

Function board GND track as you described in the other thread looks fine.

All of the test points measured between 2.8-3.1 ohms. As reference I measured from one phono ground connection to the other and it measured 0.9 ohms.

So it seems like there are no broken connections at the points you specified. However, is the higher ohm reading significant?

It might be worth saying that two of the four E’s on the electrolytic board were a little more finicky to get a reading. One in particular was more problematic. I would get a reliable reading on the upper part and some points on the lower part, but some other points would get nothing. It doesn’t look cracked or anything else problematic.


Check Function board GND track from from phono 1 & 2 inputs (P1&P2
on trackwork) No burnt track.

RED multimeter probe connected to PHONO GND connection.
In turn, measure resistance at each of the following points
Note, test at solder joint/blob or metal tab not at bare wire

Function Board, white outer wrap, middle (clear insulated) wire
Function B, orange wrap, middle (clear) wire
Function B, brown wrap, middle (clear) wire
Function B, red wrap, middle (clear) wire
Volume B, orange wrap, middle (clear) wire
Volume B, brown wrap, middle (clear) wire
Volume B, red wrap, middle (clear) wire
Volume B, yellow wrap, middle (clear) wire
Electrolytic B, tab/pin EM
Electrolytic B, tab/pin ES (2 pins, test each)
Electrolytic B, tab/pin E (4 pins, test each)
Speaker A, Black speaker post Left then repeat for right
Left Power amp, black wire, pin "E" repeat for right power amp
Left Power amp, black wire, pin "e" repeat for right power amp
AUX-1 RCA connector, outer, either L or R channel
PRE-OUT RCA connector, outer, either L or R channel
Power supply/relay board, solder blob E

Expect 1-2 ohms, the measurements at the RCAs may be higher
due to oxidation.
 
Did you remove the function board at any stage, eg, to determine measurement points
for adjustment. 2.8-3.1ohms is just a little high for my liking.

The grounding is via that rear/RCA board to the chassis (black wire). From there it
goes via the function board to the rest of the amp. All GND connections pass through the
function board. Since all resistance measurements are about the same, expect the problem
to be early in the chain.

Check black GND wire is secure to chassis, serrated/lock washer used?
Also check the solder connection of this wire to the RCA board.

Check Resistance between Phono GND and any solder blob on GND plane (highlighted).
If it's less than 2.8-3.1ohms then remove function board connector and clean pins.

upload_2018-7-8_15-32-55.png
 
Thanks mbz!

I tested the GND plane as you highlighted to the right (tested many solder points) and didn’t find anything different. However, I’m unsure about the highlight to the left. I know one of those pins/solder blobs you asked me to test earlier, but it looks like you highlighted the trace below the group of five solder points. If you meant that trace, I can say that the leftmost solder point and the connecting point to the right fail when testing.

I did turn something up that might be significant. In the photo below the two circled areas I think should be ground pins—they connect to the centre clear-wrapped wires going to the function board.

I tested the circled one on the left and it was measuring about 0.2 ohms. Then I tested the circled one on the right (and the adjacent pins in case I got it wrong) and there was nothing.

This brings up two things. 1) Why are the ohms so much higher at the solder blob at the function board? 2) Why is there no GND to a pin on the right?
 

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As reference I measured from one phono ground connection to the other and it measured 0.9 ohms.
I assume if you touch the probes together you get about 0.8ohms, so the 2.8-3.1ohms is annoyingly high.

If the measurements on the function board ground plane (highlighted in above pic above the word "Function") was 2.8-3.1 ohms then the problem is earlier on.
Check the solder connection at P1 GND highlighted. I've also highlighted the GND track that sometimes burns.

upload_2018-7-9_11-14-19.png

The highlight on those 5 pins was for the connector that should be cleaned if the GND plane measurement gave less than 2.8ohms, not the case, so move on.

Regarding you pix. The left pin P1 GND (0.2ohms) is connected to the chassis, this confirms that connections from here to the chassis are ok.
The right pin P2 GND is open, this is expected, it's purpose is to provide the GND connection to Phono 2. You should clean/deoxit the left pin in particular.
Also give the socket/female a bit of a spray.

With 0.2 ohms between left pin (female) and phono GND and 2.8-3.1 ohms between function board GND plane point to,
- clean left pin (male and female)
- check solder connection of GND P1 on function board. Maybe post a hi res pic of this area.
 
I really appreciate your continued help!

I sprayed deoxit on the connector and pins in question and it solved the high ohm issue :) I realised my former 0.9 measurement was a mistake. I’ve been getting closer to 0.2 ohms on solid connections and after spraying I’m getting 0.4 ohms or less everywhere on the function board. On the other test points you gave I’m getting 1.2 ohms or less.

However, the hum remains...

I’m not sure if you saw that plugging an RCA cable into the pre-out jacks reduces the hum a lot. Probably to 30% the volume.

I’ve attached a photo of the function board as you requested.
 

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The pix of the function board looks ok, there is some coating removed, the problematic area is highlighted.

upload_2018-7-10_10-6-33.png

Good that the resistance measurements are under control. The 2.8-3.1 ohms was just a little too high.
The observation with the pre-out/main in and RCA cable is a good one, though puzzleing. Kinda suggest
the RCA is completing the GND path with coupler switch ON, however the GND path is not part of the
coupler switching. Will have a look at this.
 
The observation with the pre-out/main in and RCA cable is a good one, though puzzleing. Kinda suggest
the RCA is completing the GND path with coupler switch ON, however the GND path is not part of the
coupler switching. Will have a look at this.
The sucker bet is that you have a bad solder connection(s) at the pre-out/main in RCA's.
Again with the measurements. Coupler switch ON, no RCA cables, measure resistance between Left Pre out GND/outer to Left Main in GND.
Repeat Left Pre out GND to Right Pre OUT GND and then to Right main IN GND. And finally Right Main in GND to Left Main IN GND. Expect less than 1 ohm for all.
Repeat the above with coupler switch off.
 
I did the testing you suggested and all combinations measured 0.4 ohms or less.

I really appreciate you continuing to make suggestions. It’s frustrating that this is so elusive (for me, at least) and I appreciate you persevering. I suspect if the unit were in your hands you could find whatever needs to be found relatively quickly.
 
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