Firing up an SX 1980 after recap - Need Help
- Thread starter JohninOOB
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Thanks Zebulon1! I wasn't sure anybody was following anymore. It's been a real pita to sort this thing out and my time to work on this thing is very limited but I'm fully committed to seeing this endeavor through so please stayed tuned. Incidentally I want to correct myself in saying all boards are connected. The Power Amps are still disconnected. Tonight I went ahead and ordered new components I didn't already have for the EQ board. At present I cannot get it to trick out at all, no matter how long it sits powered up. Rock solid so far. Thanks for checking in! I appreciate that.
John
John
hurt hand: typing hurts like fire in forearm. not on much lately. even mousing hurts. mouse and type with left hand.
one 2sa726's in each eq amp channel, get rid of them
power inputs all have 100 ohms on them.
rock solid now BUT IS eq disconnected?
one 2sa726's in each eq amp channel, get rid of them
power inputs all have 100 ohms on them.
rock solid now BUT IS eq disconnected?
Hello MTF,
Yes he EQ board is completely removed. I de-soldered the plastic rails but before I did that I disconnected pins 1 and 7 and still got it to trick out. I also replaced the signal path caps with Silmic 11s which had come in but no change. At that point I pulled the board and everything settled down. Volts shot to where they should be and was very stable. Even the lamps look brighter and the hum from the transformer has almost disappeared. Just acts much healthier with the board removed and I can no longer get it to do it's trick. I thought of doing a 6-way on the transistors but if the "ghost" is waiting for certain conditions to trick out I may not see anything. I went and ordered all new transistors.
I happen to have a couple KSA992FBU's on hand so I'll go ahead and replace the 2sa726's and post the results, UNLESS of course you meant remove and not replace? Myself not being a sparky guy one never knows.
I took voltages of the EQ transistors when it was tricked out and found the following shown in the pics:
Yes he EQ board is completely removed. I de-soldered the plastic rails but before I did that I disconnected pins 1 and 7 and still got it to trick out. I also replaced the signal path caps with Silmic 11s which had come in but no change. At that point I pulled the board and everything settled down. Volts shot to where they should be and was very stable. Even the lamps look brighter and the hum from the transformer has almost disappeared. Just acts much healthier with the board removed and I can no longer get it to do it's trick. I thought of doing a 6-way on the transistors but if the "ghost" is waiting for certain conditions to trick out I may not see anything. I went and ordered all new transistors.
I happen to have a couple KSA992FBU's on hand so I'll go ahead and replace the 2sa726's and post the results, UNLESS of course you meant remove and not replace? Myself not being a sparky guy one never knows.
I took voltages of the EQ transistors when it was tricked out and found the following shown in the pics:
Attachments
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yes, a992 in, a726 out. They are current sources, not audio.
also what rcs16 said.
inordinate current draws can hurt 100 ohm resistors.
also what rcs16 said.
inordinate current draws can hurt 100 ohm resistors.
So so news and bad news…..
Bad news - I replaced all but Q15 and Q16 transistors (didn't have them on hand) and all the 220uF caps and it does the same thing. Tricks out.
So so news - Whatever was giving me the issue has completely failed. It tricks out every time now so hopefully it will be easier to track. I disconnected EQ Amp pins 1, 3, 5, and 7 which negates any other boards and it still crashes on the + side. Pulled the board again and it returns to normal conditions with the correct volts, no hum, very stable. All other boards except Power Amps are connected.
I checked the four 100 ohm resistors and they are all good. Just have to keep plugging away until something on that board rears it's ugly head.
Bad news - I replaced all but Q15 and Q16 transistors (didn't have them on hand) and all the 220uF caps and it does the same thing. Tricks out.
So so news - Whatever was giving me the issue has completely failed. It tricks out every time now so hopefully it will be easier to track. I disconnected EQ Amp pins 1, 3, 5, and 7 which negates any other boards and it still crashes on the + side. Pulled the board again and it returns to normal conditions with the correct volts, no hum, very stable. All other boards except Power Amps are connected.
I checked the four 100 ohm resistors and they are all good. Just have to keep plugging away until something on that board rears it's ugly head.
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Chances that both channels are gone at the same time is slim unless a over voltage condition caused both to blow.
You maybe able to isolate which one of the two channels are bad by pulling one of the two pairs of 100 ohm series supply resistors, R51/R45 for the left channel and R46/52 for the right channel.
And you checked that Q15/16 are fine?
Once you figure out if only one channel is gone, compare using a powered off unit, one channel against the rest, check all bjts and resistors.
Good luck
Rick
You maybe able to isolate which one of the two channels are bad by pulling one of the two pairs of 100 ohm series supply resistors, R51/R45 for the left channel and R46/52 for the right channel.
And you checked that Q15/16 are fine?
Once you figure out if only one channel is gone, compare using a powered off unit, one channel against the rest, check all bjts and resistors.
Good luck
Rick
Hello Rick,
I dug up new Q15/Q16 out of stock for another receiver which I forgot about (we won't go there, I can just hear MTF now.) Replaced those. Checked. Same deal. I also did an in circuit 6-way check on all the transistors and found no shorts. I then pulled R45/R51 and it would no longer crash but the volts take about 2-3 seconds to creep where they should. Same issue I had before when it was on the verge of crashing. I re-installed R45/R51 and removed R46/R52 and same thing. Volts creep up at about the same rate but does not crash. For giggles I pulled all 4 resistors and it cranks right up nicely as it should. If there was something going on with that board I would expect to be able to isolate to one channel as you mentioned….but no. As I mentioned before I disconnected all pins except +34, -34, and ground and still got it to crash.
At the beginning I was focused on the PSB (+) regulator, traced it to the EQ board which was tipping it over the edge. I know that if I follow the crash back it goes as far back as the + Current Source on the PSB but I built a new one and got the same results so who knows. Is it the EQ innocently pushing it over the tipping point where it crashes something on the PSB or is it the EQ board itself. I know I'm over analyzing this. Just frustrated.
UPDATE: Got in my car, drove to RS in desperation, and picked up (4) 100 ohm 1/2 watt resistors. Stop at the store and bought a bunch of beers, went home and installed the China junk at EQ Amp R45, R46, R51, and R52. Wouldn't you know it!! ROCK SOLID, stable +34 volts flowing throughout this baby. It no longer does it's trick and runs the way it did when the board was removed.
It's been a very long journey and I'm not getting my hopes too high cause anything can happen but I have a pretty good feeling right about now. Now going to kick back a swill a few cold ones and ponder my next move. Probably replacing the Chinese stuff with something that will last. Any recommendations?
Thank you again for your help. Stay tuned. I can almost hear the music now…...
John
I dug up new Q15/Q16 out of stock for another receiver which I forgot about (we won't go there, I can just hear MTF now.) Replaced those. Checked. Same deal. I also did an in circuit 6-way check on all the transistors and found no shorts. I then pulled R45/R51 and it would no longer crash but the volts take about 2-3 seconds to creep where they should. Same issue I had before when it was on the verge of crashing. I re-installed R45/R51 and removed R46/R52 and same thing. Volts creep up at about the same rate but does not crash. For giggles I pulled all 4 resistors and it cranks right up nicely as it should. If there was something going on with that board I would expect to be able to isolate to one channel as you mentioned….but no. As I mentioned before I disconnected all pins except +34, -34, and ground and still got it to crash.
At the beginning I was focused on the PSB (+) regulator, traced it to the EQ board which was tipping it over the edge. I know that if I follow the crash back it goes as far back as the + Current Source on the PSB but I built a new one and got the same results so who knows. Is it the EQ innocently pushing it over the tipping point where it crashes something on the PSB or is it the EQ board itself. I know I'm over analyzing this. Just frustrated.
UPDATE: Got in my car, drove to RS in desperation, and picked up (4) 100 ohm 1/2 watt resistors. Stop at the store and bought a bunch of beers, went home and installed the China junk at EQ Amp R45, R46, R51, and R52. Wouldn't you know it!! ROCK SOLID, stable +34 volts flowing throughout this baby. It no longer does it's trick and runs the way it did when the board was removed.
It's been a very long journey and I'm not getting my hopes too high cause anything can happen but I have a pretty good feeling right about now. Now going to kick back a swill a few cold ones and ponder my next move. Probably replacing the Chinese stuff with something that will last. Any recommendations?
Thank you again for your help. Stay tuned. I can almost hear the music now…...
John
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lol, I'm not an ogre...
later when I can think straight, I'll look at this again, and try to figure out WHAT was going on...
later when I can think straight, I'll look at this again, and try to figure out WHAT was going on...
Well that is good news.
I find it odd that the 100 ohm series R's are the cause of the problem, even if they short out, it should not cause a PS fault!!
Recommendations for 100 ohm 1/2W R's?, so many of them to chose, since there is nothing special about them, try Vishay or KOA Speer, (standard Mouser stuff) are good, no guarantee that they are not made in China too, have to check.
Usually w/w R's are better for this application, the inductance can only help reduce HF noise.
Ohmite are a good US mfg, try, although more expensive than a metal film type
http://ca.mouser.com/Passive-Compon...tors-Through-Hole/_/N-7fx9i?P=1yzbppyZ1z0x8ah
I find it odd that the 100 ohm series R's are the cause of the problem, even if they short out, it should not cause a PS fault!!
Recommendations for 100 ohm 1/2W R's?, so many of them to chose, since there is nothing special about them, try Vishay or KOA Speer, (standard Mouser stuff) are good, no guarantee that they are not made in China too, have to check.
Usually w/w R's are better for this application, the inductance can only help reduce HF noise.
Ohmite are a good US mfg, try, although more expensive than a metal film type
http://ca.mouser.com/Passive-Compon...tors-Through-Hole/_/N-7fx9i?P=1yzbppyZ1z0x8ah
Hi Rick,
I understand what you're saying about the resistors being the culprit. I can't understand how it would produce the +34 crash with a shorted resistor(s). MTF may be able to sort that out. For now I'm keeping my fingers crossed.
Just a thought but I de-soldered, re-soldered wires here and there going through this whole process and maybe that had something to do with fixing whatever was bringing it down(?). I think that's a long shot because I performed a ton of conductive tests through this whole process and found no broken, loose, or crossed wires. All the solders looked good except for a few on the Tone Control board that I fixed. Not sure but I'm not looking into the rear view mirror any longer than I have to. I still have a few caps I want to replace, using the Similac ll in the signal path but after that I'll take another reading of all the volts and post. Also, thanks for the resistor info. I'll look into that because I'd feel a better not having RS stuff in that expensive receiver, unless a higher power than me tells me it's OK of course.
MTF, I certainly wasn't figuring you to be an ogre! You've been hanging in with me on this issue for months and there isn't anything I can say that truly speaks of my gratitude and thankfulness for all your help. Way above and beyond what I ever expected. Thank you!! I can promise this. I learned a lot of lessons (so far) with this receiver. Mainly TEST YOUR WORK after each board. Don't blow through shotgunning an entire receiver then expect everything to be perfect. Risky business as I've learned the hard way. Stay tuned.....
Thank you! John
I understand what you're saying about the resistors being the culprit. I can't understand how it would produce the +34 crash with a shorted resistor(s). MTF may be able to sort that out. For now I'm keeping my fingers crossed.
Just a thought but I de-soldered, re-soldered wires here and there going through this whole process and maybe that had something to do with fixing whatever was bringing it down(?). I think that's a long shot because I performed a ton of conductive tests through this whole process and found no broken, loose, or crossed wires. All the solders looked good except for a few on the Tone Control board that I fixed. Not sure but I'm not looking into the rear view mirror any longer than I have to. I still have a few caps I want to replace, using the Similac ll in the signal path but after that I'll take another reading of all the volts and post. Also, thanks for the resistor info. I'll look into that because I'd feel a better not having RS stuff in that expensive receiver, unless a higher power than me tells me it's OK of course.
MTF, I certainly wasn't figuring you to be an ogre! You've been hanging in with me on this issue for months and there isn't anything I can say that truly speaks of my gratitude and thankfulness for all your help. Way above and beyond what I ever expected. Thank you!! I can promise this. I learned a lot of lessons (so far) with this receiver. Mainly TEST YOUR WORK after each board. Don't blow through shotgunning an entire receiver then expect everything to be perfect. Risky business as I've learned the hard way. Stay tuned.....
Thank you! John
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So far so good…
I filled the signal path with Silmic ll caps and re-tested. No issues. Took some readings at the PSB:
Pin 18 = -77.2
Pin 17 = +78.3
Pin 9 = +34.4
Pin 11 = -34.0
Pin 13 = +12.7
Pin 14 = +12.7
Pin 16 = +7.7
Pin 15 = +4.8
Pin 6 = -.026
Pin 3 = -.026
Pin 7 = +12.9
Pin 8 = -29.0
Main Caps:
Pin 7 = +90.0
Pin 6 = -90.0
Pin 5 = -90.0
Pin 4 = +90.0
To be continued:
I filled the signal path with Silmic ll caps and re-tested. No issues. Took some readings at the PSB:
Pin 18 = -77.2
Pin 17 = +78.3
Pin 9 = +34.4
Pin 11 = -34.0
Pin 13 = +12.7
Pin 14 = +12.7
Pin 16 = +7.7
Pin 15 = +4.8
Pin 6 = -.026
Pin 3 = -.026
Pin 7 = +12.9
Pin 8 = -29.0
Main Caps:
Pin 7 = +90.0
Pin 6 = -90.0
Pin 5 = -90.0
Pin 4 = +90.0
To be continued:
OK. I set the DC Offset per MTF and zebulon1's instructions and I got the DC offset down to 3mV on both channels. I couldn't get it lower than that. Is that a problem?
Next I set the Idle Current and got the right channel dead on. The left channel was this, between pins:
24-10 = 29mV
23-11 = 38mV
18-16 = 43mV
According to the SM they are supposed to be the same across the board. Any thoughts?
At point I decided to hook up an antenna and headphones and…HOLY CRAP!!! This thing boots!! Doesn't this thing sound nice in FM anyway. I was concerned capping the Tuner board would screw up the alignment but it seems to be OK. Could probably be dialed in better but I'm not complaining.
Next problem: The phono does not work. I connected a turntable up to both Phono 1 and Phono 2 and neither work. I connected the turntable up to Aux and it works. Something still going on with the EQ board?
Another problem: When I run my hand even near the Main Bass control knob on the Tone Control board a horrendous hum/hiss occurs. The closer I get the worse it is. Can't touch the post as it would certainly damage something.
I know I'm really wearing out my welcome hear but I truly do think I'm close.
Thanks again for all your help!
-John
Next I set the Idle Current and got the right channel dead on. The left channel was this, between pins:
24-10 = 29mV
23-11 = 38mV
18-16 = 43mV
According to the SM they are supposed to be the same across the board. Any thoughts?
At point I decided to hook up an antenna and headphones and…HOLY CRAP!!! This thing boots!! Doesn't this thing sound nice in FM anyway. I was concerned capping the Tuner board would screw up the alignment but it seems to be OK. Could probably be dialed in better but I'm not complaining.
Next problem: The phono does not work. I connected a turntable up to both Phono 1 and Phono 2 and neither work. I connected the turntable up to Aux and it works. Something still going on with the EQ board?
Another problem: When I run my hand even near the Main Bass control knob on the Tone Control board a horrendous hum/hiss occurs. The closer I get the worse it is. Can't touch the post as it would certainly damage something.
I know I'm really wearing out my welcome hear but I truly do think I'm close.
Thanks again for all your help!
-John
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According to the manual, it should be 30mV and at least between 20 and 40mV. The higher the bias current means more static heat dissipated, but usually also means lower distortion, especially at 20Khz.
An bias current imbalance between pairs is a result of device mis-match. You could try multiple output devices to try to get a better balance of the pairs.
Check out the phono eq bias voltages against the schematic, if okay, apply a 1-10mV signal at 1KHz and trace it through to the selector switch and the tape(rec) outputs.
An bias current imbalance between pairs is a result of device mis-match. You could try multiple output devices to try to get a better balance of the pairs.
Check out the phono eq bias voltages against the schematic, if okay, apply a 1-10mV signal at 1KHz and trace it through to the selector switch and the tape(rec) outputs.
If you are sticking with the original output devices - you are stuck with those readings.
New replacements (with all that mechanical fooling around to mount them) will be a lot closer, depending upon if they are all from the same batch...
BUT imho, in this case I would leave it be. Risk vs reward and all that...
Since it's yours, you should record the readings and check them every year or two to see if the difference increases. Easy to do.
You DID regrease the outputs, right?
I had a power supply a long time ago, that had 4 power transistors in parallel. One was inadequately mounted and it got hotter than the rest, causing it to overheat and hog more and more of the load itself, until it shorted. Pulled shorted one out, ran on three at 3/4 power max until I could get a set of four from the same lot.
New replacements (with all that mechanical fooling around to mount them) will be a lot closer, depending upon if they are all from the same batch...
BUT imho, in this case I would leave it be. Risk vs reward and all that...
Since it's yours, you should record the readings and check them every year or two to see if the difference increases. Easy to do.
You DID regrease the outputs, right?
I had a power supply a long time ago, that had 4 power transistors in parallel. One was inadequately mounted and it got hotter than the rest, causing it to overheat and hog more and more of the load itself, until it shorted. Pulled shorted one out, ran on three at 3/4 power max until I could get a set of four from the same lot.
Hello Gentlemen,
I indeed forgot to grease the outputs. I went back and did that and the reading are the same. Below is the list I used to recap the Power Amps. I'm not sure if it is complete but this is the one I found and used at the time:
Power Amp Board (L) (GWH-109)
GWH-109: C1: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C3: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C35: .22uF 25v CSSA: 667-ECQ-V1H224JL .22uF 50v
VR1: 150K ohm multi offset: 652-3296P-1-204LF
VR3: 100 ohm single bias: 652-3386H-1-101LF
Q33: 2SC869: 512-KSC1845FTA
Power Amp Board (R) (GWH-110)
GWH-109: C2: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C4: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C36: .22uF 25v CSSA: 667-ECQ-V1H224JL .22uF 50v
VR2: 150K ohm multi offset: 652-3296P-1-204LF
VR4: 100 ohm single bias: 652-3386H-1-101LF
Q34: 2SC869: 512-KSC1845FTA
Not knowing enough about the electronics of these boards there are other transistors that were left as is. If they were not on the list I didn't mess with them. I will study the schematic and perform the check as rcs16 mentioned and takes some voltages to see if I can find something amiss.
The humming when you place your hand close to to the Main Bass control post makes me nervous but I also noticed something similar in a 1050 I have that has never been recapped. Touch the Volume knob and a slight but distinct hum is heard through the speakers or headphones.
Have a great Labor Day weekend!! John
I indeed forgot to grease the outputs. I went back and did that and the reading are the same. Below is the list I used to recap the Power Amps. I'm not sure if it is complete but this is the one I found and used at the time:
Power Amp Board (L) (GWH-109)
GWH-109: C1: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C3: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C35: .22uF 25v CSSA: 667-ECQ-V1H224JL .22uF 50v
VR1: 150K ohm multi offset: 652-3296P-1-204LF
VR3: 100 ohm single bias: 652-3386H-1-101LF
Q33: 2SC869: 512-KSC1845FTA
Power Amp Board (R) (GWH-110)
GWH-109: C2: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C4: 100uF 100v CEA: 647-UPW2A101MHD 100uF 100v
GWH-109: C36: .22uF 25v CSSA: 667-ECQ-V1H224JL .22uF 50v
VR2: 150K ohm multi offset: 652-3296P-1-204LF
VR4: 100 ohm single bias: 652-3386H-1-101LF
Q34: 2SC869: 512-KSC1845FTA
Not knowing enough about the electronics of these boards there are other transistors that were left as is. If they were not on the list I didn't mess with them. I will study the schematic and perform the check as rcs16 mentioned and takes some voltages to see if I can find something amiss.
The humming when you place your hand close to to the Main Bass control post makes me nervous but I also noticed something similar in a 1050 I have that has never been recapped. Touch the Volume knob and a slight but distinct hum is heard through the speakers or headphones.
Have a great Labor Day weekend!! John
Hum sounds like a grounding issue to me. Check that any screws that attach the circuit boards to their mounts are firmly seated and making good contact. Also, there's sometimes wires attached to ring terminals screwed or soldered to various parts of the chassis that may have come loose or broken. Recheck the solder joints of the specific switches in question where the hum is most pronounced to.
Hello John,
I spent a little time with it last night focusing on the hum. The solder joints on the Tone board pots looked OK but I re-soldered them anyway along with a couple other spots and got the same hum. I flipped the Tone switch off and still get the hum but it's minimized. Not nearly as pronounced. I also checked the volts going into the board which was good at + & - 34V respectively but the readings after all 4 resistors were either + or - 18V. The schematic says 13V so I don't know what's going on there. All the voltage readings across the board seem a little high and if I touch the DMM probe across the bases of any of the 4 transistors it let's out a pretty loud hum.
Checked for loose wires or posts and found none.
That's as far as I got. I'll take another crack at it tonight.
Thanks! John
I spent a little time with it last night focusing on the hum. The solder joints on the Tone board pots looked OK but I re-soldered them anyway along with a couple other spots and got the same hum. I flipped the Tone switch off and still get the hum but it's minimized. Not nearly as pronounced. I also checked the volts going into the board which was good at + & - 34V respectively but the readings after all 4 resistors were either + or - 18V. The schematic says 13V so I don't know what's going on there. All the voltage readings across the board seem a little high and if I touch the DMM probe across the bases of any of the 4 transistors it let's out a pretty loud hum.
Checked for loose wires or posts and found none.
That's as far as I got. I'll take another crack at it tonight.
Thanks! John
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