Rebuilding Protection Board Didn't Help?

[ZeroJunk]

Protection board on SX-1010 still cutting out occassionally even after re-working. DC offset is 4 or 5 mV at most. Bias is 50 mV after it settles. I can record the min/max DC offset while it's playing if that will tell us anything.

Thanks for any suggestions.

 

[ZeroJunk]

Well, it's been playing now for about an hour at 1/3 volume and is hanging in there. Pin 13 on the regulator board is 32.4V instead of 35V but the rest are on the money. I have it turned up on it's side playing. Just wondering if there is something squirrly on the regulator board that stays cooler in this position that could cause it to go in to protection if it gets hotter.

 

[markthefixer]

Watch the pin 1 and 3 voltages to see if they are guilty.

When it goes into protection, does it STAY, or just momentarily pop out and back in? If it stays it's easier to track down, BUT we can lift some of those diodes to eliminate other inputs.

If it's on board, then just do the two 2sc945's and the 2sa733 with

512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.06 ea
512-KSC1845EBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.06 ea

 

[ZeroJunk]

Well, it looks like it's not going to trip now until I put the cover back on it.

I recorded the min/max voltage on pin one and three.

Pin three over a 1/2 hour period was -3.2 to 6.8 mV

Pin one was -70.4 to 120.8 mV But, the peaks are almost instantaneous and it's hard to catch them with your eye.
I guess I should add the redings are with music playing. With volume at zero pin one is stable at 3.2 mV and pin three at about 2 mV.

I'll let it play all afternoon and see if it will go in to protection. It was staying in from fifteen or twenty seconds to several minutes when it tripped.

It's been playing now for six hours and no problem. Why do I know that as soon as I put the cover back on it will trip.:scratch2:

 

[markthefixer]

Well, it looks like it's not going to trip now until I put the cover back on it.

I recorded the min/max voltage on pin one and three.

Pin three over a 1/2 hour period was -3.2 to 6.8 mV

Pin one was -70.4 to 120.8 mV But, the peaks are almost instantaneous and it's hard to catch them with your eye.
I guess I should add the redings are with music playing. With volume at zero pin one is stable at 3.2 mV and pin three at about 2 mV.

I'll let it play all afternoon and see if it will go in to protection. It was staying in from fifteen or twenty seconds to several minutes when it tripped.

It's been playing now for six hours and no problem. Why do I know that as soon as I put the cover back on it will trip.:scratch2:

The circuit makes allowances for the ac content of the waveform, and really will only trigger when the ac and dc badly diverge.

You COULD aim a hairdryer around a bit to see if you can drive it over the edge...
How about posting one of your excellent pictures of the power supply, plus I'll take a bit of time later to see what transistors could benefit from a beefing up or heatsinks.
I had an intermittent on maddarts 1010 for the tuner power that was driving me nuts, until I apparently cleared it up by replacing the power transistor and the series resistor (which both tested ok), you may just want to do something similar.

 

[ZeroJunk]

As you can see it's original. Has a little cooked look to it doesn't it?

I don't know whether this tells you anything, but the problem showed up originally when I was A/B ing the tuner with an external tuner through the aux. at low volume to see the difference in quality. Coincidence?

 

[markthefixer]

My primary suspicion is Q8, it takes 56v and through a 330 ohm resistor turns it into 35v, which runs the protection circuit, including the relay.

Q8 is an itty bitty to-92 package, a to-126 package would be a lot better. It can dissipate 1.2 watts when bare and 10 watts heatsunk.

This is the same mod as the infamous Q5 & Q7 on the sx-950.

use a
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
or
512-KSC2682YSTU to-126 ecb 180v .1a 1.2/8w 200mhz 100-320hfe $0.31 ea

I had been recommending the 2682, as the circuit wouldn't pull over 100mA, but the 2690 doesn't seem to sacrifice anything, and can handle more current. Plus the 126 case has no exposed metal that could short, thus any added heat sink would be electrically cold, unlike a to-220 case.

If you want to go nuts, you could get either:
512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
or go whole hawg and use:
863-MJE15033G pnp to-220 bce 250v 8a 50w 30mhz hfe:70 $0.87
863-MJE15032G npn to-220 bce 250v 8a 50w 30mhz hfe:70 $0.87
in place of the d313's (Q1,Q7:npn) and the b507(Q4np) on the heatsink aready.

I would worry slightly about the 1/4 watt series resistors R11,R12 & R21 at 10 ohms and R20 at 3.3 ohms, because if they were abused they just might have been made intermittent instead of popping outright, like a fuse.

But I would expect that just a Q8 replacement is warranted.

 

[ZeroJunk]

Thanks, the 35 volts was the worst variance from spec., actually started off at about 31 and slowly came up. I'll switch out Q8 and see what happens.

These old receivers have a sweet sound. I actually like it better than my SX-1250.

Thanks for your time.

 

[ccheath]

These old receivers have a sweet sound. I actually like it better than my SX-1250.

Interesting, I have the same thought. I thought I was crazy.

 

[ZeroJunk]

Interesting, I have the same thought. I thought I was crazy

More than that, I was comparing it back and forth with a F99X through the aux. input that did very well in the shootouts and the internal tuner in the SX-1010 was noticeably fuller and just as sensitive.

 

[ZeroJunk]

Confounded thing. I replace Q8 and everything played right along, perfect 35 volts. I put the covers back on and put it in the shop where I am most of the time. It played about 20 minutes and shut down. I flipped the switch off waited a few seconds flipped it on and it came back on. Then it played maybe 30 minutes and cycled off. I flipped the switch off waited a few minutes flipped it back and it came back on. Now it's been playing for 7 hours, no problem. I'm just going to leave it on 24 hours a day until it quits. Unless I get bored, then I may take a hair dryer to it. Thought about soaking it in salt water and dropping it off the house.

 

[markthefixer]

sx-1010 AWR054 power supply rebuild

I'll get a under 5(? w/o shipping) buck list together to do the power supply pass transistors and a few resistors. That's how I conquered maddarts power supply problem.

I should have just stressed that from the start.

Q4 2sb507
one 512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

Q1 Q7 2sd313
two 512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54 ea

Q8 2sc1384 (ecb)
one 512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
or one 512-KSC2682YSTU to-126 ecb 180v .1a 1.2/8w 200mhz 100-320hfe $0.31 (preferred, the current is below 0.1 amp)

Q5 Q6 2sa628 (BCE)
two 512-KSA1013YBU to-92 ecb 160v 1a .9w 50mhz 160-320hfe $0.17 ea

Q2 Q3 2sc869 (bce)
two 512-KSC2383YBU to-92 ecb 160v 1a .9w 50mhz 160-320hfe $0.17 ea

D8 D9 wz-032
two 512-1N5257B Fairchild 33 V, 0.5W zener $0.05 ea

D10 wz-014
one 512-1N5244B Fairchild 14 V, 0.5W Zener $0.05

two ten ohms 1/4 watt metal film 660-MF1/4DC10R0F 0.06 ea
one 3.3 ohms 1/4 watt metal film 660-MF1/4DC3R30F 0.06

was the power supply recapped?
ok, here's the caps:
C7 & C8 470uf (80v) 100v 647-UPW2A471MHD $1.87 ea
C10, C11 100uf (63v) 100v 647-UPW2A101MHD $0.87 ea
C12 & C13 100uf (35v) 63v 647-UPW1J101MPD1TD $0.37 ea
C14 47uf 50v 647-UPW1H470MED $0.25
C18 1000uf (35v) 50v 647-UPW1H102MHD1CV $0.98
C19 220uf (16v) 35v 647-UPW1V221MPD $0.41
C20 & C21 2200uf 10v 647-UPW1A222MHD $0.80 ea

extra parts just in case somebody's looking :
D1 D2 D3 D4 SIB01 100v 1amp
D5 D6 D7 1S1885 100v 1amp
512-1n4004 conventional rectifier 1a 400v $0.06 ea

 

[ZeroJunk]

was the power supply recapped?

No, I was hoping to get by without it. But, I guess I had better just rebuild the whole thing.



How do we know that it is the power supply and not something going south in the amp? The lack of any noise or distortion?

 

[markthefixer]

No, I was hoping to get by without it. But, I guess I had better just rebuild the whole thing.



How do we know that it is the power supply and not something going south in the amp? The lack of any noise or distortion?

Part of it. We would have to run some wires outside the closed case, power supply and protection inputs - and the thing would have to STAY in protection. Or use the hairdryer and NOT be sure that whatever we find was caused by the more intense hairdryer heat.

As it is, we are whittling down the possibilities - we're pretty sure we can trust the protection circuits now, so we either exonerate the power supply by a lot of time intensive monitoring or remove the likely culprits that have proven guilty in other units.

Why do you think EW, Rabbi Rich and others run their "finished" work so long - to find these little pests that like to hide...

 

[ZeroJunk]

OK. I'll get the stuff ordered and get on it. Thanks for the list.

 

[Stereo_75]

Hey Zerojunk if you can post some pics of your work, this is fascinating, all of us can learn from this.

OK. I'll get the stuff ordered and get on it. Thanks for the list.

 

[ZeroJunk]

Stereo 75, I'll get to this eventually. I have 18 chainsaws in the shop, most need a piston or piston and cylinder. I have been spending most of my extra time on those, and that's where I use the SX-1010. It has not gone in to protection and has been running all day for several days. I know these things don't fix themselves, but it's hard to get motivated when it is working perfectly. I'm reallly posting this because I know as soon as I say something it will get contrary again.:yes:

 

[ZeroJunk]

Well, the SX-1010 started going in and out of protection again. Ordered evrything to rebuild the power supply board yesterday.

Just curious, is it worthwhile to beef up the heatsink as some have done? Opinions?

 

[markthefixer]

If you have good ventilation around it, there are quite a few out there that haven't baked their power supplies to death.

BUT if you can figure out how to bolt on some extra fins, it definitely won't hurt.

 

[redd6054]

This might be a silly question , can a small computor cooling fan be used some-how, in the case maybe so that it is hidden? taken off of the transformer somewhere?
cheers Wolfgang