SX-1010 question

[KA3JRT]

Hi, everyone... I am restoring an SX-1010, and have worked my way through the "usual suspects" of known defective components. I am still having a problem with erratic tripping of the protection circuit, so there is more work to do. Looking at the BOM list that was put up a while back, I see that some parts are now obsolete, especially the main filter capacitors and at least one of the transistors. Does anyone have an updated list?

TIm

 

[kwayde]

You should find the problem and fix that problem before you restore.

 

[markthefixer]

You should find the problem and fix that problem before you restore.

Right!!!

which of the "usual suspects" have you replaced?

Plus there are multiple "lists" floating around. If you don't reproduce the one you are using for us, at least POINT to it.

Calling yourself KA3JRT implies a Radio Amateur License, is that so?

 

[merlynski]

Is the protection circuit tripping while playing music or while just sitting there with no input?

 

[KA3JRT]

To answer the questions... I have replaced the transistors and electrolytic capacitors on the control amplifier board, the transistors and electrolytic capacitors on us equalizer board, the 2SA726 and 2SC1451 transistors on both amplifier boards, as well as the electrolytic capacitors and the trimpots on those boards. I have completely rebuilt the power supply regulator board and the protection board. The DC offset and bias adjustments are correct. The receiver drops in and out of protection at random times, usually for a second or two; it seems to need to warm up for a while before the problem starts.

The list that I am going by is from a post by Junfan, on 3-17-16. Yes, I am a ham, licensed since the early 1980s. I'm an experienced bench technician, so I am used to this kind of work.

 

[merlynski]

Your description of symptoms typically points first to the relay driver transistor, Q7, originally a 2SC1384, on the AWM-082 Protection PCB. Did you already replace it with a KSC2690AY?
If the cause of the relay dropping was coming in through a properly operating Protection circuit it would stay dropped for the normal 3-6 second time delay.
A detected power amp fault will show as the dcv on the cathodes of D5, D6, or D7 being pulled negative from their normal voltage of about +17 to +20vdc. An AC loss on pin 12 will also cause the relay to drop. Any of those conditions would reset the timer by discharging C6.

 

[zebulon1]

I would double check the solder connections on the protection board.
Something seems fishy.

 

[KA3JRT]

Yes, the relay driver transistor has been replaced. I'm now test running it, and waiting for it to cut out. I did go over the connections on the protection board, and replaced the two blue Sanyo electrolytic capacitors. So far, so good.

 

[KA3JRT]

I am still fighting it! This evening, I installed the two replacement power supply filter capacitors. It cut out two or three times, and the left channel made a little pop. After that, it was fine. All the connections seem OK, and no amount of prodding anywhere will make it trigger. It does drop out for about 3 or 4 seconds each time.

I'm a long experienced tech, but this one is driving me nuts.

 

[merlynski]

3 or 4 seconds is likely the protection circuit normal delay. If the return delay is the same every time, and you are getting a pop out of the speakers just as the relay drops, that points at an amplifier fault rather than a protection circuit fault.

 

[KA3JRT]

Well, it seems to be fixed. I replaced all of the transistors on both audio driver boards, reset the bias and offset, and resoldered a lot of connections. I wound up using the TTA04B and TTC04B transistors to replace the 2SB528 and the 2SD358, and they work fine. I also replaced both main filter capacitors as a preventive measure.

It has been playing for four days, with no problems.