Help —SX-838 disaster

[merlynski]

Protection pcb AWM-025.

Pin 2, -13vdc: -13.07vdc OK
Pin 11, +35vdc: +32.47vdc OK
Pin 1, 0vdc: +9.27vdc bad positive dc offset
Pin 3, 0vdc: -8.38vdc bad negative dc offset
Pin 10, +35vdc: +32.47 OK
Pin 9, about +9vdc: 8.18vdc is the relay pulled in? With those offsets this should be 0vdc. Unless they are cancelling each other out, but that still leaves the combined input to the detector (base Q4) at +0.89vdc, which should drop the relay.
Cathode D5, about +20vdc or more: +16.5vdc
Cathode D6, about +20vdc or more: +16.71v dc
Cathode D7, about +20vdc or more: +17.01vdc

Pin 5 +0.02vdc should be about the same as pin 1 ??
Pin 6 - 0.17vdc should be about the same as pin 1 ??
Pin 7 -8.36vdc expected related to pin 3 offset
Pin 8 -8.51vdc expected related to pin 3 offset

My readings are in blue. Please note that D3 cathode is reading 0.018; D4 cathode -0.588 - - - yes that is negative
Measure ACV on pin 12, 7.5vac: 7.54vac. -0.21vdc OK
Has this unit worked properly for you in the past? Has someone else worked on it before you?

Please post dc voltages from the -031, pin 1, 2, 5, 20, 24, 25.

EDIT: I reread the whole post and saw it has been yours for a long time.

 

[dustmaker]

Protection pcb AWM-025.

Pin 2, -13vdc: -13.07vdc OK
Pin 11, +35vdc: +32.47vdc OK
Pin 1, 0vdc: +9.27vdc bad positive dc offset
Pin 3, 0vdc: -8.38vdc bad negative dc offset
Pin 10, +35vdc: +32.47 OK
Pin 9, about +9vdc: 8.18vdc is the relay pulled in? The relay seems to function correctly. I hear it engage about one second after powering on. With those offsets this should be 0vdc. Unless they are cancelling each other out, but that still leaves the combined input to the detector (base Q4) at +0.89vdc, which should drop the relay.
Cathode D5, about +20vdc or more: +16.5vdc
Cathode D6, about +20vdc or more: +16.71v dc
Cathode D7, about +20vdc or more: +17.01vdc

Pin 5 +0.02vdc should be about the same as pin 1 ??
Pin 6 - 0.17vdc should be about the same as pin 1 ??
Pin 7 -8.36vdc expected related to pin 3 offset
Pin 8 -8.51vdc expected related to pin 3 offset

My readings are in blue. Please note that D3 cathode is reading 0.018; D4 cathode -0.588 - - - yes that is negative
Measure ACV on pin 12, 7.5vac: 7.54vac. -0.21vdc OK
Has this unit worked properly for you in the past? Yes. Has someone else worked on it before you? Yes/probably. I started off gung-ho and bought a bunch of caps and transistors and replaced a lot of parts on the 031, 025 and 011. When it wouldn’t work, I figured it was best to start over. I was able to buy parted out replacements for those three boards so I replaced all three boards to get the receiver back to an initial stage. I don’t know the history of those boards. The 031 looks like it had work done on it but the 011 and 025 look original. After replacing everything, I re-found this forum

Please post dc voltages from the -031, pin 1, 2, 5, 20, 24, 25.

EDIT: I reread the whole post and saw it has been yours for a long time.

Pins on the the -031
P1. 41.6
P2. -41.5
P5. -8.47
P20. 9.45
P24. -41.5
P25. 41.6[/QUOTE]

 

[merlynski]

Yes/probably. I started off gung-ho and bought a bunch of caps and transistors and replaced a lot of parts on the 031, 025 and 011. When it wouldn’t work, I figured it was best to start over. I was able to buy parted out replacements for those three boards so I replaced all three boards to get the receiver back to an initial stage. I don’t know the history of those boards. The 031 looks like it had work done on it but the 011 and 025 look original. After replacing everything, I re-found this forum

OK, that history helps. I was wondering if there are mis-connected wires, so knowing you replaced the boards tells me to be aware of the possibility when I see readings that don't match.

Pins on the the -031
P1. 41.6
P2. -41.5
P5. -8.47
P24. -41.5
P25. 41.6

Power supply feeds to the board for output transistors look good.
Remove the output transistors Q11, 12, 13, 14 from the heatsink and set them aside. Make note of which came from where.
Recheck orientation of the transistors on the AWH-031. Something is causing serious dc on the output pin 5 and 20. That has to be fixed before we can finish the protection pcb. If you find any installed incorrectly replace them, as they likely have been damaged when powered up.

-031 Pin 20, 14, 9, 17, 18 dcv also please.

Note that there are low resistances (0.5Ω) connected between/to some of these so measure very carefully on lowest Ω range and compare wire colors at both ends. If there is a mis-wire please correct it, but let me know where it was connected before correction. That will also help clear things up.

Check for wired connection from AWH-031 pin 22 to AWM-025 pin 6 (0Ω)
Check for wired connection from AWH-031 pin 23 to AWM-025 pin 5 (0Ω)
Check for wired connection from AWH-031 pin 4 to AWM-025 pin 7 (0Ω)
Check for wired connection from AWH-031 pin 3 to AWM-025 pin 8 (0Ω)

Check for wired connection from AWH-031 pin 20 to AWM-025 pin 1 and Relay pin 5 (0Ω)
Check for wired connection from AWH-031 pin 5 to AWM-025 pin 3 and Relay pin 7 (0Ω)

Note that when you add information inside a quote from a previous post in a new post it does not display properly, the post looks like it only contains the quote.

EDIT: correct typos

 

[dustmaker]

Yes/probably. I started off gung-ho and bought a bunch of caps and transistors and replaced a lot of parts on the 031, 025 and 011. When it wouldn’t work, I figured it was best to start over. I was able to buy parted out replacements for those three boards so I replaced all three boards to get the receiver back to an initial stage. I don’t know the history of those boards. The 031 looks like it had work done on it but the 011 and 025 look original. After replacing everything, I re-found this forum

OK, that history helps. I was wondering if there are mis-connected wires, so knowing you replaced the boards tells me to be aware of the possibility when I see readings that don't match.

Pins on the the -031
P1. 41.6
P2. -41.5
P5. -8.47
P24. -41.5
P25. 41.6

Power supply feeds to the board for output transistors look good.
Remove the output transistors Q11, 12, 13, 14 from the heatsink and set them aside.
Recheck orientation of the transistors on the AWH-031. Something is causing serious dc on the output pin 5 and 20. That has to be fixed before we can finish the protection pcb. If you find any installed incorrectly replace them, as they likely have been damaged when powered up.

-031 Pin 20, 14, 9, 17, 18 dcv also please.

Note that there are low resistances (0.5Ω) connected between/to some of these so measure very carefully on lowest Ω range and compare wire colors at both ends. If there is a mis-wire please correct it, but let me know where it was connected before correction. That will also help clear things up.

Check for wired connection from AWH-031 pin 22 to AWM-012 pin 6 (0Ω)
Check for wired connection from AWH-031 pin 23 to AWM-012 pin 5 (0Ω)
Check for wired connection from AWH-031 pin 4 to AWM-012 pin 7 (0Ω)
Check for wired connection from AWH-031 pin 3 to AWM-012 pin 8 (0Ω)

Check for wired connection from AWH-031 pin 20 to AWM-012 pin 1 and Relay pin 5 (0Ω)
Check for wired connection from AWH-031 pin 50 to AWM-012 pin 3 and Relay pin 7 (0Ω)

Note that when you add information inside a quote from a previous post in a new post it does not display properly, the post looks like it only contains the quote.

Thank you. - I really do appreciate your effort and advice. A couple questions: you are referencing AWM-012. I’m assuming you mean AWM-025. Also you reference pin 50- I assume you mean pin 5

 

[merlynski]

You are welcome!
Yes, my typing skills are way below my electronics, thanks I will correct that.

 

[dustmaker]

I pulled out the -031 board and noticed that pin 25 was bent and touching the frame. Resistor R38 is obviously damaged, it’s almost split in two. I still have additional investigation on this board.

I then looked at my original -031 board and noticed that Q5 and Q6 were both put in backwards.

So with two boards, both with issues, which one should I focus on? I’m assuming both boards have burnt transistors. Are any transistors on either board salvageable? What about the output transistors?

 

[merlynski]

Unless the board itself is damaged beyond repair it is rebuildable. I would pick the one that is already installed. Are you actually disconnecting the wires?
I would not salvage any transistors, except maybe output transistors. If you have a blown base resistor (R38) on an output transistor the output and driver are probably damaged. Most of the small signal transistors are very cheap if you buy 10 or 100 at a time, like I do from Mouser. FWIW don't buy parts from auction sites, they are way overpriced and may well be fake. You can salvage resistors if they measure in spec, modern metal film are likely better. Electrolytic caps get old and dry out - replace, don't try and salvage.
With as much likely damage as there is seen from the tests we have done I would do all new transistors on the -031.
Here are a couple of links to good info:
Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements
Low Noise Small Signal Transistors
Bipolar Junction Transistor Testing Basics

 

[dustmaker]

One other thing...is there a way for me to test the -031 once known problems are fixed without fully connecting the board?

Unless the board itself is damaged beyond repair it is rebuildable. I would pick the one that is already installed. Are you actually disconnecting the wires?
I would not salvage any transistors, except maybe output transistors. If you have a blown base resistor (R38) on an output transistor the output and driver are probably damaged. Most of the small signal transistors are very cheap if you buy 10 or 100 at a time, like I do from Mouser. FWIW don't buy parts from auction sites, they are way overpriced and may well be fake. You can salvage resistors if they measure in spec, modern metal film are likely better. Electrolytic caps get old and dry out - replace, don't try and salvage.
With as much likely damage as there is seen from the tests we have done I would do all new transistors on the -031.
Here are a couple of links to good info:
Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements
Low Noise Small Signal Transistors
Bipolar Junction Transistor Testing Basics

i did remove the board and disconnected the wires as I couldn’t see how else to access the foil side of the -031 board for replacement. Fortunately, my iPad took nice clear pictures and I’ve been making notes on what pin goes to what board/pin. I have a couple wire wrapping tools and some 22awg wire to replace any short runs of basic colors but I can’t seem to find any stripped wire or even solid 20awg 600v red, white, green wire. Can I substitute 18guage instead? Any source for hookup wire where I don’t have to buy 100ft at a time?

 

[merlynski]

I can't imagine that 18 gauge would not work. Make sure you are using solid copper, not CCA (copper clad aluminum) as you will get corrosion and not a proper wrap gas tight weld. If the board is removed I would pick the one that has the best physical condition and completely rebuild it, all new silicon and electrolytics. Ceramic caps don't need replaced. Some of the electrolytic signal caps can be replaced with film caps.

If you pre-test the transistors and verify correct installation you should be able to reinstall the pcb, then power up on DBT (leave Outputs uninstalled) and verify basic functionality.

 

[dustmaker]

Ok - it’s going to take me a week or so as I’m missing some capacitors. From a previous sx-838 post, replacement capacitors are shown. Two of those listed, both film capacitors, are now obsolete. Any recommendations for the two obsolete part #s?

C1, C2 1 25v. ECQ-V1H105JL3. Obsolete
C3, C4 .47 25v ECQ-V1H474JL3. Obsolete
C7, C8 UPW1A330MDD

 

[merlynski]

Lots of those Panasonics have gone obsolete, I think most of the guys that do this a lot are using WIMA or KEMET caps.
These might work if they fit (Mouser#):
0.47 50v 80-MMK5474K50J01L4
1 63v 80-R82DC4100Z360J
Both have 5mm lead spacing.
Sourced from other AK lists originally, but now in my Mouser project list.

 

[dustmaker]

Update - I placed an order with Mouser and I expected it on Thursday. It didn’t arrive and after reviewing my account, I realized one item was back ordered, so my entire order is being held. I’m working on canceling and reordering. Hopefully, I can get this sorted out Monday and I can receive my parts at the end of the week

 

[merlynski]

Update - I placed an order with Mouser and I expected it on Thursday. It didn’t arrive and after reviewing my account, I realized one item was back ordered, so my entire order is being held. I’m working on canceling and reordering. Hopefully, I can get this sorted out Monday and I can receive my parts at the end of the week

Mouser will ship everything but the backorder if you tell them to, and usually, if its a small item, not charge for shipping when it does come in. What was backordered?

 

[dustmaker]

Mouser will ship everything but the backorder if you tell them to, and usually, if its a small item, not charge for shipping when it does come in. What was backordered?

25 - 330/10 capacitors were back ordered. I’m trying to cancel that line and choose a different capacitor. I sent an email to Customer service late Friday, but I guess they don’t work on Saturday/Sunday. Hopefully I can resolve today.

the other item I’m having trouble with is finding solid copper wire that doesn’t come in 100ft+ rolls. And I can’t find any striped wire. Question- is there any significance to the wire color in this receiver (and others). In the Pioneer, black is ground and red and white are power source, but I can’t make sense of the color scheme. In household AC electrical, black and red are hot with green being ground.

 

[merlynski]

Orange is usually the main raw negative dc supply, red is the main raw positive supply, black is used for common/ground. That is as close to a 'standard' as I have figured out. I have not had my hands on enough units to make any other judgements. Good luck with striped wire. The big factory I worked in used to stripe their own wire, had a big machine.
Amazon has assortment rolls of solid colors of different gauges, make sure you get pure copper, not Copper Clad Aluminum (CCA).
Example: https://smile.amazon.com/22GA-Hook-...ords=copper+hookup+wire&qid=1590941023&sr=8-7

 

[dustmaker]

That helps. You mentioned in a previous post that I can test the -031 just by connecting the input wires. That would be pin 1. Red - pin 25. From -055 p4
Pin 2. White - pin 24. From -055 p5
Pin 12 white From -025 p2
Pin 14. Red. From -055 p13

all other pins are output. Is this a correct observation?

 

[merlynski]

That helps. You mentioned in a previous post that I can test the -031 just by connecting the input wires. That would be pin 1. Red - pin 25. From -055 p4
Pin 2. White - pin 24. From -055 p5
Pin 12 white From -025 p2
Pin 14. Red. From -055 p13

all other pins are output. Is this a correct observation?

I see 8 power supply pins (power in of various voltages), 5 ground, 2 signal inputs and 2 signal outputs, as well as 4 protection sensor outputs, plus output transistor connections. All of the power pins and the grounds must be connected to do some static dc testing. And that will not be comprehensive.
Which previous post are you referring to?

 

[dustmaker]

I see 8 power supply pins (power in of various voltages), 5 ground, 2 signal inputs and 2 signal outputs, as well as 4 protection sensor outputs, plus output transistor connections. All of the power pins and the grounds must be connected to do some static dc testing. And that will not be comprehensive.
Which previous post are you referring to?

Post 28 I asked if I could test without fully connecting the -031. On post 29 you said “If you pre-test the transistors and verify correct installation you should be able to reinstall the pcb, then power up on DBT (leave Outputs uninstalled) and verify basic functionality.”. I assumed you were replying to my question. But from your last post, it seems like I will have to basically connect all pins.

 

[merlynski]

Post 28 I asked if I could test without fully connecting the -031. On post 29 you said “If you pre-test the transistors and verify correct installation you should be able to reinstall the pcb, then power up on DBT (leave Outputs uninstalled) and verify basic functionality.”. I assumed you were replying to my question. But from your last post, it seems like I will have to basically connect all pins.

Yes, there was a communication breakdown, by 'Outputs' I meant Output transistors. All the other connections would still be needed (reinstall the pcb). As the output transistors are the most expensive power amp components and the most likely to be damaged during preliminary testing, if there is a problem, they are frequently left disconnected/uninstalled, for first vetting of the power amp section. Pre-testing was about the small signal transistors and driver transistors. Sorry for the confusion. In this power amp architecture it will still dc balance properly and you can pre-check everything but setting bias, before installing the output transistors.

 

[dustmaker]

I’ve received my parts and replaced on the 031. I removed the output transistors as suggested an reinstalled and I have the following (stepping off your earlier comment)

Protection pcb AWM-025.

Pin 2, -13vdc: -12.95
Pin 11, +35vdc: 32.53
Pin 1, 0vdc: -0.2.
Pin 3, 0vdc: was 30.45 Now measuring -34
Pin 10, +35vdc: OK 32.5
Pin 9, about +9vdc: 32.5
Cathode D5, about +20vdc or more: 32.56
Cathode D6, about +20vdc or more: About. 3.3
Cathode D7, about +20vdc or more: About 3.5

Pin 5 should be about the same as pin 1 ?? Yes
Pin 6 should be about the same as pin 1 ?? Yes
Pin 7 expected related to pin 3 offset. Yes
Pin 8 expected related to pin 3 offset. Yes

Please post dc voltages from the -031, pin 1, 2, 5, 20, 24, 25.
P1. 41.5
P2. -41.4
P5. -34.2
P20. -.2
P24 -41.4
P25. 41.5

Check for wired connection from AWH-031 pin 22 to AWM-025 pin 6 (0Ω)
Check for wired connection from AWH-031 pin 23 to AWM-025 pin 5 (0Ω)
Check for wired connection from AWH-031 pin 4 to AWM-025 pin 7 (0Ω)
Check for wired connection from AWH-031 pin 3 to AWM-025 pin 8 (0Ω)

Check for wired connection from AWH-031 pin 20 to AWM-025 pin 1 and Relay pin 5 (0Ω)
Check for wired connection from AWH-031 pin 5 to AWM-025 pin 3 and Relay pin 7 (0Ω)

- Merlynski-

I was checking continuity as stated above and I also have continuity between many pins that I shouldn’t have so I suspect I have one or more shorts on the 031 pcb. since I’ve been into it several times, I want to try and address some of my issues before I ask for more specific help. On pin 3 of the 025 I initially had too much positive voltage then it went to large negative Voltage the next time I tested it so I probably blew a transistor. My current plan is to remove the 031 and test it alone for continuity and if I find shorts I’ll fix. Then without the 031, I’ll test continuity on the other boards in total, zero in and fix where I find problems. Since I’ve removed the boards and replaced, I have to rule out a miss wiring on the pins also. Once I have these areas addressed I’ll come back for your professional assistance, but I feel pretty silly having you walk me through some of these basic issues and you’ve already helped demystify some of the structure of these old electronics so I am not as completely clueless as I was a few weeks ago. Yes, still pretty dumb, but I’m learning. Fortunately, I bought multiples of components for just such an occasion. Again, thank you for your guidance.


it will likely be a few days before I’m able to get through this (household maintenance such as a leaking dishwasher has taken priority)