The caps are all new. Transistor sub is a question, as the 2SC369 has higher lc than likely modern replacements (such as 2SC1845). I don't know how to determine if this would be an issue in these circuits.
SX-1000TD Odd problem - hoping for some help
- Thread starter spark1
- Start date
The caps are all new. Transistor sub is a question, as the 2SC369 has higher lc than likely modern replacements (such as 2SC1845). I don't know how to determine if this would be an issue in these circuits.
Mañana
Made some progress.. There is a small board between the balance pot (the last stage of the control amp's output) and the input into the power amp section....W15-01. Not on the schematic nor mentioned anywhere in the service manual. Six small value caps and a few resistors
Decided to replace all, and touched up the joints on the balance pot. Seemed to help. Sound is more balanced now, and seems to be full range on both channels. Getting normal tone control and loudness function on both channels.
I can see (hear) why my friend has fond memories of this old receiver...it may not be as linear nor precise as later/better amps, but it has a nice sound...full and comfortable, warmish, but with good clarity and "punch". Sounds pretty darned good thru the bench speakers (Minimum 7s) in my small workshop.
I would still be interested in suggestions/thoughts as regards:
Decided to replace all, and touched up the joints on the balance pot. Seemed to help. Sound is more balanced now, and seems to be full range on both channels. Getting normal tone control and loudness function on both channels.
I can see (hear) why my friend has fond memories of this old receiver...it may not be as linear nor precise as later/better amps, but it has a nice sound...full and comfortable, warmish, but with good clarity and "punch". Sounds pretty darned good thru the bench speakers (Minimum 7s) in my small workshop.
I would still be interested in suggestions/thoughts as regards:
- Replacement of 2SC629 transistors
- Increasing the capacitance of the speaker output caps
- Any other updates or preventive maintenance I should do
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merlynski
Curmudgeon Electronicist
Here I was studying the schematic and making a plan of attack and suddenly it is fixed! Good for you!
I did a search on the Pioneer forum, no mention of the W15-01 PCB except in your thread. Is that something you could document and post a schematic and a picture of both sides?
I did a search on the Pioneer forum, no mention of the W15-01 PCB except in your thread. Is that something you could document and post a schematic and a picture of both sides?
I was too optimistic. Sound is better, but still a bit lower/thinner on right channel. Mild distortion/low level hash in that channel as well.
If I knew what to use I'd replace the 8 2SC629 transistors on preamp and tone amp and see if things get better.
I will sketch out a schematic and post pics of that mysterious little board this weekend. A Google search showed one for sale on eBay. It was represented as having come from an SX-1000TD. Here is link:
https://www.ebay.com/itm/PIONEER-W15-010-PCB-SX-1000TD-STEREO-RECEIVER-/112381484939?redirect=mobile
If I knew what to use I'd replace the 8 2SC629 transistors on preamp and tone amp and see if things get better.
I will sketch out a schematic and post pics of that mysterious little board this weekend. A Google search showed one for sale on eBay. It was represented as having come from an SX-1000TD. Here is link:
https://www.ebay.com/itm/PIONEER-W15-010-PCB-SX-1000TD-STEREO-RECEIVER-/112381484939?redirect=mobile
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uamauka
New Member
https://audiokarma.org/forums/index.php?threads/sx-1000tw-restore.786866/
See this thread for assurance on use of 1845 transistor in place of 369- ( where they show 458 - as on schematic). It seems to have worked for them. I'm still waiting for parts before finishing up mine.
See this thread for assurance on use of 1845 transistor in place of 369- ( where they show 458 - as on schematic). It seems to have worked for them. I'm still waiting for parts before finishing up mine.
Thx. I will take a look tomorrow.
Guess I will go ahead and replace the 2SC369s on the preamp and control amp.
If that doesn't solve it, I will replace transistors in the power amp section (if I can detemine suitable substitutes).
I think this is a case where an oscilloscope is just about required to isolate where the signal is getting corrupted.
If that doesn't solve it, I will replace transistors in the power amp section (if I can detemine suitable substitutes).
I think this is a case where an oscilloscope is just about required to isolate where the signal is getting corrupted.
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Replaced transistors on pre and control/tone boards. No joy.
Same as has been the case with other changes made, upon initial power up I thought the problem was finally resolved. But after running for 5-10 minutes the right channel output gets quite noticeably "thinner" than the left. Whatever is causing the problem apparently doesn't do so until warmed up.
The bass tone control and loudness function still provide quite a bit less boost on the right channel than on the left channel, once the problem manifests. They seem to work fine for the first few minutes.
I've gone through the cycle several times now...power off, let is set for 30 minutes or so, fire it up and all is good. Then, within 5-10 minutes, I'm back to lower output and distortion on the right channel.
I wonder if it could be either the speaker coupling or filter caps. Could they cause this kind of symptom? I will be replacing them when parts arrive next week.
Could it be one of the right channel output transistors? Is swapping them R2L/L2R worth the effort?
Same as has been the case with other changes made, upon initial power up I thought the problem was finally resolved. But after running for 5-10 minutes the right channel output gets quite noticeably "thinner" than the left. Whatever is causing the problem apparently doesn't do so until warmed up.
The bass tone control and loudness function still provide quite a bit less boost on the right channel than on the left channel, once the problem manifests. They seem to work fine for the first few minutes.
I've gone through the cycle several times now...power off, let is set for 30 minutes or so, fire it up and all is good. Then, within 5-10 minutes, I'm back to lower output and distortion on the right channel.
I wonder if it could be either the speaker coupling or filter caps. Could they cause this kind of symptom? I will be replacing them when parts arrive next week.
Could it be one of the right channel output transistors? Is swapping them R2L/L2R worth the effort?
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One other observation, FWIW...when comparing R to L using balance pot, in addition to being of lower output and sounding thinner (not as much bass), the right channel starts breaking up and distorting (clipping?) earlier than the left channel. In other words, at the same point on volume control, the right channel is distorting/breaking up while the left channel is still clear (no break-up, no distortion), and notably louder.
Discovered this when trying to see how much more volume had to be applied to get the right channel to be as loud as the left.
If there is a decent likelihood that the problem is the filter or output caps, I will wait until I get them in next week before trying anything else. If the caps are not very likely to be the cause, I'll try swapping the output transistors tomorrow.
Thoughts?
Discovered this when trying to see how much more volume had to be applied to get the right channel to be as loud as the left.
If there is a decent likelihood that the problem is the filter or output caps, I will wait until I get them in next week before trying anything else. If the caps are not very likely to be the cause, I'll try swapping the output transistors tomorrow.
Thoughts?
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merlynski
Curmudgeon Electronicist
Just a bit of humor - throwing things . . .
Do you see any DC building up at the outputs, like an output cap is leaking? Try monitoring the signal side of R41 with no audio, no speakers, just watch for DC leakage.
Do you have a signal tracer? How about another small audio amp, or an unused set of computer speakers to make a signal tracer.
On the channel that is failing monitor the center voltage, W15-027, pin 9. Should be about +41 volts (half of +B, +82vdc), see if it drifts off center. This is the same kind of thing like DC offset in a dual +/- supply amp, that splits the driver transistor and output transistor columns. Also monitor the bias to see if it is drifting as the unit warms up, DCV across R30. If those drift off it will tell you it is the output stage, if they are stable it is probably before the output stage.
Do you see any DC building up at the outputs, like an output cap is leaking? Try monitoring the signal side of R41 with no audio, no speakers, just watch for DC leakage.
Do you have a signal tracer? How about another small audio amp, or an unused set of computer speakers to make a signal tracer.
On the channel that is failing monitor the center voltage, W15-027, pin 9. Should be about +41 volts (half of +B, +82vdc), see if it drifts off center. This is the same kind of thing like DC offset in a dual +/- supply amp, that splits the driver transistor and output transistor columns. Also monitor the bias to see if it is drifting as the unit warms up, DCV across R30. If those drift off it will tell you it is the output stage, if they are stable it is probably before the output stage.
To monitor DC building up on the outputs, do you mean measure across the speaker terminals, with a load on them? Or on the collectors (cases) of the output transistors?
Or just measure at signal side of R41?
No signal tracer, but I'm game for building one.
Does monitoring center voltage serve same purpose as monitoring R41?
Or just measure at signal side of R41?
No signal tracer, but I'm game for building one.
Does monitoring center voltage serve same purpose as monitoring R41?
petehall347
the brandy coffee man
i just go for the output transistor cases .the collectors .
merlynski
Curmudgeon Electronicist
R41 is on the output (speaker) side of the output capacitor, if there is any real dc current leakage through the output capacitor it will drain through R41 and show up as a pretty constant dc voltage. If you have a speaker or additional load on the output it will draw down the leakage and make it less apparent.
That does not serve the same purpose as monitoring the center voltage, which is on the amplifier side of the output capacitor, and has the large dc voltage on it. It is electrically the same as the collector of Q4 or the + side of C8, the output cap.
You can monitor the center voltage with the amp sitting idle or you can play music until it distorts, then kill the input and measure the dc level while it is still warmer from being active.
That does not serve the same purpose as monitoring the center voltage, which is on the amplifier side of the output capacitor, and has the large dc voltage on it. It is electrically the same as the collector of Q4 or the + side of C8, the output cap.
You can monitor the center voltage with the amp sitting idle or you can play music until it distorts, then kill the input and measure the dc level while it is still warmer from being active.