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SX-1000TD Odd problem - hoping for some help

I know exactly what you mean. I was looking at buying an older Tek 475, two channel, 200MHz analog scope, there was one on the evilbay for about $425 with shipping. And that is not a bad price for what it is. Clean looking, 100% seller, said freshly calibrated. Looked really good. And it is a model I have used before. But for that money you can buy a new (chinese or other-wise) modern one with all the bells and whistles. I have a 60Mhz digital, fine for audio, but I don't much care for it. But is is better than no scope, and it was given to me by a friend, so I use what I got. I have spent so much time in front of those old analog scopes I don't even need to think about how to use it, the new-fangled ones, with menus and readouts just feel complicated.
 
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I don't even know how to use one. It would be a good thing to learn, before actually buying one.

I'm going to go down to the shop today and do a micro-level examination of all solder joints and traces. Problem seems to come and go (mostly come), which to me suggests either a bad switch/pot, a bad transistor or a bad joint/trace.

Pots and switches don't seem to be the problem, since I can't ever get any of them to provide even momentary effect on the problem. Transistors are all new (except outputs), so they are low likelihood.
 
I agree with your conclusions. That intermittency also supports the oscillation theory, sometimes it starts, sometimes it doesn't.
It does not rule out any of the other things you mentioned either, though. Or a cracked trace, or intermittent cap problem.
There are free downloadable software oscilloscope apps that use the sound inputs of a phone, tablet or computer. But they are limited to the audio range of the sound circuitry in the unit. Might help you get familiar with the concepts, though.
There are hardware imported units around $150. If you are just looking at audio anything above 20MHZ will do, if you are thinking about FM receiver signal work you need at least 100MHZ, 200MHZ is better. Two channels is a must in my mind, and an external trigger option (usually there).
 
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Just to make sure I am on the same page, unit has passed the DBT and are on full mains power, correct?
Are the output transistors installed or uninstalled?
 
Yes, they were set after initial repair, again after distortion repair, and again after new components. Both are fairly stable after, especially after warm up. Left channel drifts up and down by a few mV once in a while...never by more. Set bias at 30mA (manual says 20ma).
 
I have reread this whole thread.
Is the lack of Bass control and Loudness effect still present on the R channel?
 
W15-047anno.png
Look closely (test if possible) the components in the blue box, above, especially the bass circuit. The audio comes into the R channel tone controls through C18 after the purple arrow. The higher frequency signals follow the red arrow through the Treble control, the low frequency signals follow the green arrow through the Bass control. They come out the other side and are summed together again in the node at the purple box. If there is an open or out of tolerance component in the base section, even with the bass control centered, the signal will be diminished in the lower frequencies. An open trace can cause similar failure. This operates independently of the High Cut and Low Cut filters.
 
The loudness and bass function seem to have little effect on the right channel (the problematic channel). I will go over this part of the board again.

Sorry for slow response...been out of town.
 
So I started working to identify that section of the control board, and realized that the board in this unit is very different. This one has more capacitors, with different values, and different resistors. Also, the circuit itself is different. It does use the same transistors.

I then spent some time looking at the control board from other versions of the SX-1000 and could not find one that matched. Documentation on this unit is relatively scarce.

I will keep trying to find a schematic or board layout that matches the one in the unit I'm working on.
 
In looking at the schematic for the control amp board of the SX-1000TA (W15-006), it appears to be quite similar to the one in my unit. This might make sense, given that my unit also has the W15-001 notch filter board, which appears in the 1000TA schematic, but is not in the 1000TD service manual or schematic.

I will spend some time this afternoon trying to match my control amp board to the one in the SX1000TA schematic to verify that they are indeed the same.
 
I noticed that discrepancy in other SX-1000xx threads I looked at. Yours is the first I have participated in, directly.
I will help however I can . . .
 
uamauka said:
larryderouin: Thanks, checking the other manuals turned out to be a useful tip. I had downloaded the 395 and the sx-100TW manuals but they were identical. The sx-1000TD manual had nothing new to offer, but sx-100TA manual shows a W15-006 board which closely resembles my w15-031 board. The w15-006 board has a couple extra capacitors. The sx-1000TA scematic also shows my w15-010 board. Now, of course this would be even more helpful information if I could properly read scematics, but who knows maybe I'll get there. At any rate, I'll be needing to order up a few more capacitors when I get there. I have to fix the short I made in the main amp board first.

As to the desoldering station, I'm not doing a lot of this kind of work, but I made the determination that I don't have the steady hand and patience to succeed on this project with just a solder pump and braid. So I ordered one. Did I mention I'm a fan of tools?

Bruno Primas: Yes, replacing caps and transistors is the plan. I have lots of close up pictures so hopefully I won't get too confused. Its reassuring to hear your 395 turned out quiet, that's what I'm hoping for. Other than the noise floor this 395 is in really nice shape. Maybe it won't be a foot stool after all.
Click to expand...

This is the best I found on AK Pioneer, probably the same you did.
 
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