SX-850 AWR-101 Resistor question

hertzdonut

Press Play and Stand Back
This morning, my SX-850 went silent right in middle of the first cut of Van Halen's first album. (Well, it was pushing out about 50% volume at the time...:banana:) The protection relay did not click back on, and I knew there was an issue. Waited a few minutes, applied power again, but still silence, regardless of mode (Phono, Tape, etc)

I opened her up and saw this on the AWR-101 Power Supply board. Looks like a toasted resistor. I was trying to identify it, is it R6? I'm putting an order in to Mouser for new caps and transistors, and wanted to add the correct resistor to my list. If it is R6, is this the correct one?
Resistor 293-150-RC

I notice there is no sleeve included, and Mouser doesn't seem to list them. Is it important to have that?

Thanks!

-Jeff

 
The sleeve isn't mandatory, it was to suppress flames.

You need to check the resistance of it, yes it is R6, and it does dissipate some heat - heat that would otherwise be dissipated by Q5. So the color of the sleeve is not much of an indicator.

I certainly hope the list is the upgraded one, with enhanced Q5, Q6 & Q7 in to-126 cases.
 
You need to rebuild the entire power supply board along with the protection board.
 
The sleeves on the resistor and the legs are re-useable. They are just flame retardant fiberglass and will discolor with heat. DeSolder one leg of the resistor off the board and THEN measure it.

You can order fiberglass sleeving. Or just reuse the old one.
 
Thanks for the input, guys. Flame suppression...yeah, I think I'll stick with that little bit of security! :yes:

Mark, thanks for the heads-up, I'll check the resistor tonight. Larry, thanks, I'll pop one leg off and measure it that way. And regarding the list, I believe this is current and covers all caps and transistors (Q5, Q6, and Q7 are all in TO-106 cases)

Oh, one question: Mouser shows 647-UHE2A471MHD (caps for C10 and C11) on backorder. I don't know what qualifies as a proper substitute. Any suggestions?

Thanks!

-Jeff

Power Supply Board (AWR-101)

AWR-101: C10: 470uF 80v ACH-038, CEA: 647-UHE2A471MHD 470uF 100v
AWR-101: C11: 470uF 80v ACH-038, CEA: 647-UHE2A471MHD 470uF 100v
AWR-101: C12: 2200uF 35v ACH-060, CEA: 647-UPW1V222MHD6 2200uF 35v
AWR-101: C13: 1000uF 25v CEA: 647-UPW1E102MPD6 1000uF 25v
AWR-101: C14: 220uF 10v CEA: 647-UPW1V221MPD6 220uF 35v
AWR-101: C15: 470uF 63v CEA: 647-UPW1J471MHD 470uF 63v
AWR-101: C16: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
AWR-101: C18: 47uF 50v CEA: 647-UPW1H470MED 47uF 50v
AWR-101: C19: 47uF 35v CEA: 647-UPW1V470MED 47uF 35v
AWR-101: C20: 100uF 63v CEA: 647-UPW1J101MPD6 100uF 63v
AWR-101: C21: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
AWR-101: C23: 100uF 35v CEA: 647-UPW1V101MPD 100uF 35v

Q1: 2SD313P: 512-KSC2073H2TU
Q2: 2SB507P: 512-KSA940TU
Q3: 2SC1318: 512-KSC2383OTA
Q4: 2SA720: 512-KSA1013YBU
Q5: 2SC1318: 512-KSC2690AYS
Q6: 2SA720: 512-KSA1220AYS
Q7: 2SC1318: 512-KSC2383YBU
Q8: 2SD313: 512-KSC2073H2TU
Q9: 2SD313: 512-KSC2073H2TU
Q10: 2SC869: 512-KSC2383OTA
 
Between bites of my sandwich at lunch, I managed to grab my DMM and do a quick check on the R6 resistor. The numbers quickly climbed up and and locked in on 150.0. I guess there's nothing wrong with it after all.

Granted, I hadn't desoldered one leg it per Larry's suggestion, but I'm guessing it will read the same. Or I could be completely wrong. It's happened before, just ask my wife!:nono:
 
That resistor in it's circuit should read ok, no reasonable sneak current paths capable of lowering or spoofing the reading. Depends upon the circuit.

Doesn't surprise me, they get hot, and rarely fail, while they CAN discolor the sleeve...

647-UPW2A471MHD was the original cap, the upM was a sub for out of stock when that list was made.

It would be a good idea to do the protect board as well, save on shipping costs, and since you are "in there"...

Protection Circuit Assembly (AWM-062)

AWM-062: C1: .22uF 10v CSSA: 667-ECQ-V1H224JL2 .22uF 50v
AWM-062: C2: .22uF 10v CSSA: 667-ECQ-V1H224JL2 .22uF 50v
AWM-062: C3: 330uF 6.8v CEA: 647-UPW1A331MPD 330uF 10v
AWM-062: C4: 330uF 6.8v CEA: 647-UPW1A331MPD 330uF 10v
AWM-062: C5: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWM-062: C6: 100uF 16v CEA: 647-UPW1V101MPD 100uF 35v

AWM-062: Q6: 512-KSC2383YTA
AWM-062: Q7: 512-KSC2690AYS
512-1n4004 added. pins 9, 10(cathode, the banded end)
 
Excellent, thanks Mark! I'll hunt up that sub, and yeah, it probably would be a good idea to bring that protect board up to snuff. And tsd is probably on the money too.
 
won't see it before early next week, have a great 4th weekend. :D

I have some pyrotechnics to dispose of / celebrate.. this is the first 4th of July after a certain law was implemented that I had worked for extensively (more than all of this century - it LONG predates my AK involvement) and I swore that when it came to pass, I was gonna make a LOT of noise. We snatched quite a plum out of the teeth of the Chicago Democrat machine.
 
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Thanks, Mark, you too!

And enjoy making things go boom. On purpose, no less. :thmbsp:

Also, congrats on the plum-snatching. That in itself is worth at least one 16-shot Emerald City cake.
 
OK, parts rolling in today. Cool.

I hate to ask a dumb question, but...As I reviewed the list, I then searched the 850 schematic, the block diagram, the actual board itself (AWM-062), and I have no idea where that rectifier goes (512-1n4004: pins 9, 10. cathode, the banded end); I mean, I know Mark spelled it out at pins 9 and 10, but obviously I'm overlooking notation somewhere, because I'm not seeing any indications of numbers (other than post numbers, of course)

What am I missing?

Jeff
 
OK, parts rolling in today. Cool.

I hate to ask a dumb question, but...As I reviewed the list, I then searched the 850 schematic, the block diagram, the actual board itself (AWM-062), and I have no idea where that rectifier goes (512-1n4004: pins 9, 10. cathode, the banded end); I mean, I know Mark spelled it out at pins 9 and 10, but obviously I'm overlooking notation somewhere, because I'm not seeing any indications of numbers (other than post numbers, of course)

What am I missing?

Jeff

512-1n4004 added. pins 9, 10(cathode, the banded end)

This means to wrap the leads around the pins on the board it goes to pin 9 and pin 10 and the banded end is on 10
 
Ohhh, so I'm not replacing any diodes, just adding a new one to bridge between pin 9 (what I was actually calling a post) and pin 10.

Simple enough. Thanks, goat67! :thmbsp:
 
While you are there stick a 1N4004 at D8, and check all other diodes on that board.
 
Recap and transistor replacements done, both boards.

Powered up, still no click of the relay, no sound. Lights all working, FM tuner Stereo lights illuminate when tuning into a station.

Ohhh-kay. On to measurements...my results are in parentheses. Red is suspect, green is good.

AWR-101 board, these are regulated voltages, unless otherwise indicated. the voltage readings are ground referenced:
pins 2 & 3 +5.4v dc (+.5v dc, 5 min later: +.7dc, 10 min later: +1.5v dc)
pins 4 & 5 +13.9v dc (+13.8v dc)
pins 6 & 7 +51.5 v dc (+51.6v dc)
pins 8, 9 & 10 +36.5v dc (+37.4v dc)
pin 11 +28v dc (+29v dc)
pin 13 -13.5v dc (-13.2v dc)
pin 14 -51.5v dc (-50.5v dc)
pin 15 -19v dc (-18.4v dc)
pin 17 - raw unregulated dc to the outputs, (-44.3)
pin 18 + raw unregulated dc to the outputs (+44.3)

AWM-062 protection board
pin 11 +36.5v dc (+37.5v dc)
pin 2 -13.6v dc (+13.8v dc)
pin 12 7.5v AC (+7.4v AC)
pin 1 audio input, good would be dc millivolts, bad can go up to over 30v
(+.047v dc)

pin 3 audio input, good would be dc millivolts, bad can go up to over 30v
(+10.5v dc)


I don't know why pins 2 & 3 on AWR-101 kept slowly climbing. If I had more time, I would've left the receiver on and checked again in 30 minutes.
Based upon the info I've gathered above, what's my next step?

Thanks in advance!

-Jeff
 
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two separate problems.

pins 2&3:
Pins 4 & 5 exonerate the D11 zener, so R21, C14, R22 are suspect. Check for a reversed C14. Check the resistances if C14 in correctly.
Then check that Q9 and Q10 are also installed correctly.

pin 3:
This is why I like ALL protection board pin voltages, pin 7 and 8 voltages might have been useful.

Didn't you try to set the dc offset on the channels? Assuming everything was done correctly in that channel.
OK, before that
check/post the voltages at each end of VR1 and VR2. just look at the voltage at each end, do not disturb the wiper. four measurements.
let's see if the adjustment capabilities of each pot is in the correct voltage range.
 
two separate problems.

pins 2&3:
Pins 4 & 5 exonerate the D11 zener, so R21, C14, R22 are suspect. Check for a reversed C14.
Checked C14, verified installed correctly.


Check the resistances if C14 in correctly.
R21: 3.3
R22: went to 2.4, continued to slowly climb. I didn't wait 10 minutes to see where it would stop.


Then check that Q9 and Q10 are also installed correctly.
Q9 and Q10 checked and verified installed correctly.


pin 3:
This is why I like ALL protection board pin voltages, pin 7 and 8 voltages might have been useful.
You call, I haul.
Pin 7: +10.6v dc
Pin 8: +10.6v dc


Didn't you try to set the dc offset on the channels? Assuming everything was done correctly in that channel.
No, I've never done that procedure. I had to search the service manual just to find where VR1 and VR2 are!


OK, before that, check/post the voltages at each end of VR1 and VR2. just look at the voltage at each end, do not disturb the wiper. four measurements.
let's see if the adjustment capabilities of each pot is in the correct voltage range.
Because I've never messed with these before, I was unsure what qualifies as "each end". So I made my best guess and stuck my negative probe to bare chassis, and then touched separately 8 pins on that board. If that's not the right way to measure, please let me know exactly where, and I'll be happy to redo.
Pin 9: 0v dc
Pin 10: +.05v dc
Pin 12: +.07v dc
Pin 13: +.03v dc

Pin 24: 0v dc
Pin 25: +10.4v dc
Pin 27: +10.4v dc
Pin 28: +10.4v dc
 
I meant to go to the actual pots on each channel, which have 3 separate connections each, one on each end and the independent, movable tap. Probably only easily accessible from the bottom of the board, unless you reference other components (R11, R13 for vr1 R12,R14 for vr2 , right next to each other all ends closest to the pot itself) connected to it and find their leads up top.
R11, R12 are 100k brown black yellow gold,
R13, R14 are 9.1k white brown red gold

The schematic and the board do NOT agree on these component designations.... Grrrrrr.... I AM REFERENCING FROM THE BOARD DRAWING AND THE TRACES ON THE BACK.

Those pots inject a counter voltage/current into the input along with the signal, that when adjusted correctly, gets the DC output voltage of the amp to 0.000v
This counter voltage/current is very small, and there are OTHER components hooked up to the pot to limit the voltages applied to the ends. If one of these components has a problem, the adjustment range is too wide, and you could get what you are seeing.
 
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