Re-capping an SX 737
- Thread starter Maron
- Start date
We're ok as long as you checked what I posted and recognized all THESE DIFFERENCES in the lead layouts from the originals to the replacemernts.
Q1 Q2 Q3 Q4 original 2sa726 (ecb) > 512-KSA992FBU (ln)to-92 ecb is same as the original
Q5 Q6 2sc1451 (ebc) > 512-KSC2310YBU to-92 ecb is scrambled...
Q9 Q10 2sb527 (bce) > 512-KSA1220AYS to-126 ecb is REVERSED from the original
Q7 Q8 2sd357 (bce) > 512-KSC2690AYS to-126 ecb is REVERSED from the original
------- output transistors (unlikely but for completeness) -----------
2sb530 > 863-MJ21193G pnp to-3 250v 16A 250W 4mhz 8-75hfe $3.83
2sd370 > 863-MJ21194G npn to-3 250v 16A 250W 4mhz 8-75hfe $3.83
The to-3's are not in. So they are not a factor, plus they are hard to reverse or whatever when socketed.
I have checked this post for accuracy from the original post, the service manual's transistor layouts, and my original records of the replacement transistor's layouts. They ARE accurate - I am relieved I made no errors that could have steered you wrong.
One thing you could try is to see if the VR3 (read pin 3 voltage to ground) and VR4 (pin 17 voltage to ground) adjustments can bring the voltages down closer to zero. VR3 and VR4 are the two adjustments in the center of the amp board, very close together.
Also please read and post ALL the voltages at ALL the existing pins (1 to 19?) on the amplifier board that you haven't already (20 to 33) posted.
I am embarrassed to say I should have told you to dial VR1 and VR2 down to minimum ohms upon replacing the transistors. They are the two pots on the outside edges of the board. I'm not sure of clockwise or counter clockwise. So use the ohmmeter with the power off.... VR1 and VR2 will STAY at zero until the power transistors are installed.
note: the DC neutral voltage and idle current procedure in the service manual incorrectly identifies adjusting VR1 (pin 3 voltage to ground) and VR2 (pin 17 voltage to ground) for 0v and VR3 (voltage between pins 2 & 1) and VR4 (voltage between pins 18 & 19) for 20 millivolts. It correctly identifies the VR1, VR2, VR3 & VR4 positions in the drawing.
the CORRECT DC neutral voltage and idle current procedure is to adjust VR3 (pin 3 voltage to ground) and VR4 (pin 17 voltage to ground) for 0v and VR1 (voltage between pins 2 & 1) and VR2 (voltage between pins 18 & 19) for 20 millivolts.
This post is finished and proof read and I'm toasted - g'nite all.....
Q1 Q2 Q3 Q4 original 2sa726 (ecb) > 512-KSA992FBU (ln)to-92 ecb is same as the original
Q5 Q6 2sc1451 (ebc) > 512-KSC2310YBU to-92 ecb is scrambled...
Q9 Q10 2sb527 (bce) > 512-KSA1220AYS to-126 ecb is REVERSED from the original
Q7 Q8 2sd357 (bce) > 512-KSC2690AYS to-126 ecb is REVERSED from the original
------- output transistors (unlikely but for completeness) -----------
2sb530 > 863-MJ21193G pnp to-3 250v 16A 250W 4mhz 8-75hfe $3.83
2sd370 > 863-MJ21194G npn to-3 250v 16A 250W 4mhz 8-75hfe $3.83
The to-3's are not in. So they are not a factor, plus they are hard to reverse or whatever when socketed.
I have checked this post for accuracy from the original post, the service manual's transistor layouts, and my original records of the replacement transistor's layouts. They ARE accurate - I am relieved I made no errors that could have steered you wrong.
One thing you could try is to see if the VR3 (read pin 3 voltage to ground) and VR4 (pin 17 voltage to ground) adjustments can bring the voltages down closer to zero. VR3 and VR4 are the two adjustments in the center of the amp board, very close together.
Also please read and post ALL the voltages at ALL the existing pins (1 to 19?) on the amplifier board that you haven't already (20 to 33) posted.
I am embarrassed to say I should have told you to dial VR1 and VR2 down to minimum ohms upon replacing the transistors. They are the two pots on the outside edges of the board. I'm not sure of clockwise or counter clockwise. So use the ohmmeter with the power off.... VR1 and VR2 will STAY at zero until the power transistors are installed.
note: the DC neutral voltage and idle current procedure in the service manual incorrectly identifies adjusting VR1 (pin 3 voltage to ground) and VR2 (pin 17 voltage to ground) for 0v and VR3 (voltage between pins 2 & 1) and VR4 (voltage between pins 18 & 19) for 20 millivolts. It correctly identifies the VR1, VR2, VR3 & VR4 positions in the drawing.
the CORRECT DC neutral voltage and idle current procedure is to adjust VR3 (pin 3 voltage to ground) and VR4 (pin 17 voltage to ground) for 0v and VR1 (voltage between pins 2 & 1) and VR2 (voltage between pins 18 & 19) for 20 millivolts.
This post is finished and proof read and I'm toasted - g'nite all.....
Last edited:
Maron
Always Learning
Your right Mark , I had Q7,8,9,10 backwards 
. I looked at the data sheet from mouser for them http://www.fairchildsemi.com/ds/KS/KSA1220A.pdf , didnt see any writing and installed them that way (one side has writing , the other doesn't) . I checked again when you asked and noticed a slight taper in the drawing , pulled one of them out and f@#k me !! backwards :tears: . I went and corrected the 4 of them . Now the readings are back to what they were the first time I took them ( before replacement ) .
20 = +33.7
21 = +34.1
22 = +36.2
23 = +33.7
24 = +33.7
25 = -36.2
26 = +33.6
27 = +33.6
28 = -36.4
29 = -36.4
30 = +33.7
31 = +34.1
32 = +36.3
33 = +36.3
I feel like were going around in circles :sigh:
At least we are rebuilding the boards , which was what I intended to do anyways . .... now if we could only get it to make music
. I looked at the data sheet from mouser for them http://www.fairchildsemi.com/ds/KS/KSA1220A.pdf , didnt see any writing and installed them that way (one side has writing , the other doesn't) . I checked again when you asked and noticed a slight taper in the drawing , pulled one of them out and f@#k me !! backwards :tears: . I went and corrected the 4 of them . Now the readings are back to what they were the first time I took them ( before replacement ) .20 = +33.7
21 = +34.1
22 = +36.2
23 = +33.7
24 = +33.7
25 = -36.2
26 = +33.6
27 = +33.6
28 = -36.4
29 = -36.4
30 = +33.7
31 = +34.1
32 = +36.3
33 = +36.3
I feel like were going around in circles :sigh:
At least we are rebuilding the boards , which was what I intended to do anyways . .... now if we could only get it to make music
Before installing new transistors you should test them, not only for functionality, but to be SURE that you have their connections properly identified.
I'm willing to bet all 4 are kaput.:tears:
You need to pull them out and test them using this protocol:
http://www.audiokarma.org/forums/showthread.php?t=43186
Read down to post #11, for a rigorous test description, sample results, and (using copy and paste - then edit in your results) reporting format.
My only concern is whether or not they took other transistors with them - we could not only be starting from scratch with the transistors, but looking for additional damaged passive parts (resistors etc...)
I'm willing to bet all 4 are kaput.:tears:
You need to pull them out and test them using this protocol:
http://www.audiokarma.org/forums/showthread.php?t=43186
Read down to post #11, for a rigorous test description, sample results, and (using copy and paste - then edit in your results) reporting format.
My only concern is whether or not they took other transistors with them - we could not only be starting from scratch with the transistors, but looking for additional damaged passive parts (resistors etc...)
Maron
Always Learning
here are the tests on the transistors .() denotes measurements taken from the old transistors:
Q7 :
black lead to base, red lead to collector, result = OL = No conduction
black lead to base, red lead to emitter, result = OL = No conduction
red lead to base, black lead to collector, result = .570v (.587v)
red lead to base, black lead to emitter, result = .570v (.577v)
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
Q8:
black lead to base, red lead to collector, result = OL = No conduction
black lead to base, red lead to emitter, result = OL = No conduction
red lead to base, black lead to collector, result = .579v (.563v)
red lead to base, black lead to emitter, result = .577v (.578v)
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
Q9:
black lead to base, red lead to collector, result = .578v (.583v)
black lead to base, red lead to emitter, result = .580v (.593v)
red lead to base, black lead to collector, result = OL = No conduction
red lead to base, black lead to emitter, result = OL = No conduction
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
Q10:
black lead to base, red lead to collector, result = .579v (.576v)
black lead to base, red lead to emitter, result = .581v (.591v)
red lead to base, black lead to collector, result = OL = No conduction
red lead to base, black lead to emitter, result = OL = No conduction
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
Q7 :
black lead to base, red lead to collector, result = OL = No conduction
black lead to base, red lead to emitter, result = OL = No conduction
red lead to base, black lead to collector, result = .570v (.587v)
red lead to base, black lead to emitter, result = .570v (.577v)
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
Q8:
black lead to base, red lead to collector, result = OL = No conduction
black lead to base, red lead to emitter, result = OL = No conduction
red lead to base, black lead to collector, result = .579v (.563v)
red lead to base, black lead to emitter, result = .577v (.578v)
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
Q9:
black lead to base, red lead to collector, result = .578v (.583v)
black lead to base, red lead to emitter, result = .580v (.593v)
red lead to base, black lead to collector, result = OL = No conduction
red lead to base, black lead to emitter, result = OL = No conduction
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
Q10:
black lead to base, red lead to collector, result = .579v (.576v)
black lead to base, red lead to emitter, result = .581v (.591v)
red lead to base, black lead to collector, result = OL = No conduction
red lead to base, black lead to emitter, result = OL = No conduction
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
SolutionRoom
...***...
So it's working and the issue was cold/loose soldering on the trannies???
Maron
Always Learning
I don't think it was those transistors . I did re-flow every solder point on the board , both old and new . Could have been a bad/cold solder on my part , or could have been an old brittle solder connection . What ever it was , re-flowing seems to have cured it . I'm just glad I didn't smoke the trannies or anything else .
Ok, I missed a lot, and misunderstood more.
After Maron re-installed the tested driver transistors , he powered up the unit and took a series of readings, and he used the previous data posted back on page 2 post 21 to interpret his readings as safe to install the output transistors.
The 2 (c) readings are the raw power to the amp,
the 2 (b) readings of +0.6v or so and -0.6v or so (it should be the same polarity as the "C" on that transistor).
the 2 (e) readings will be almost identical, and should be in the range of plus or minus 50 millivolts (usually). with no output transistors to flow current, it is essentially the dc offset voltage of the amplifier, and could be adjusted =- BUT the adjustment may not be the same once the outputs are installed.
There is a gotcha when installing output transistors on an amp that was recently turned on, the big capacitors MAY have retained a charge - which you DON'T want - sometimes there are "bleeder" resistors to discharge the big caps - and sometimes there aren't - check the collector wire voltages, and if present over say 1/2 volt, discharge them with a resistor - 3k ohms is safe, but use a pliers to hold them because they could get hot enough to burn your fingers.
A couple of notes for those that follow in the path of this thread: When replacing any transistors in an amplifier, it is a very good thing to do the following:
1. Find the idle current adjustment pot and turn it to minimum ohms for the 737 (I don't know if that is counter clockwise or clockwise) using an ohmmeter across the trimpot to be sure. Otherwise the amp could come on with TOO high of an idle current - and risking damage.
2. Put the unit on a dim bulb tester - if there's an error or something was missed, the amount of power that can flow will be limited, and thus any potential damage.
3. power it up, and then while monitoring the idle current, try to adjust the idle current on one channel to the specified value. You might not get all the way there because the dim bulb acts like a brownout, and may cause the protection to drop out because it thinks the power has been turned off at the switch. As long as the bulb doesn't go bright, you're fine.
4. after getting the idle current to the set value on one channel - TURN IT BACK DOWN TO ZERO - this is IMPORTANT - because when the dim bulb is removed - the idle current when plugged directly into the line may be way too high.....
5. now repeat steps 3 and 4 for the other channel. test the idle current, then back it off to zero.
6. NOW you can take it off the dim bulb and do the idle current and dc offset voltage adjusts for real - with minimal chances of a disaster happening.
After Maron re-installed the tested driver transistors , he powered up the unit and took a series of readings, and he used the previous data posted back on page 2 post 21 to interpret his readings as safe to install the output transistors.
This is for one output stage
The 2 (c) readings are the raw power to the amp,
the 2 (b) readings of +0.6v or so and -0.6v or so (it should be the same polarity as the "C" on that transistor).
the 2 (e) readings will be almost identical, and should be in the range of plus or minus 50 millivolts (usually). with no output transistors to flow current, it is essentially the dc offset voltage of the amplifier, and could be adjusted =- BUT the adjustment may not be the same once the outputs are installed.
There is a gotcha when installing output transistors on an amp that was recently turned on, the big capacitors MAY have retained a charge - which you DON'T want - sometimes there are "bleeder" resistors to discharge the big caps - and sometimes there aren't - check the collector wire voltages, and if present over say 1/2 volt, discharge them with a resistor - 3k ohms is safe, but use a pliers to hold them because they could get hot enough to burn your fingers.
A couple of notes for those that follow in the path of this thread: When replacing any transistors in an amplifier, it is a very good thing to do the following:
1. Find the idle current adjustment pot and turn it to minimum ohms for the 737 (I don't know if that is counter clockwise or clockwise) using an ohmmeter across the trimpot to be sure. Otherwise the amp could come on with TOO high of an idle current - and risking damage.
2. Put the unit on a dim bulb tester - if there's an error or something was missed, the amount of power that can flow will be limited, and thus any potential damage.
3. power it up, and then while monitoring the idle current, try to adjust the idle current on one channel to the specified value. You might not get all the way there because the dim bulb acts like a brownout, and may cause the protection to drop out because it thinks the power has been turned off at the switch. As long as the bulb doesn't go bright, you're fine.
4. after getting the idle current to the set value on one channel - TURN IT BACK DOWN TO ZERO - this is IMPORTANT - because when the dim bulb is removed - the idle current when plugged directly into the line may be way too high.....
5. now repeat steps 3 and 4 for the other channel. test the idle current, then back it off to zero.
6. NOW you can take it off the dim bulb and do the idle current and dc offset voltage adjusts for real - with minimal chances of a disaster happening.
Maron
Always Learning
Ok, I missed a lot, and you dodged a whole magazine of bullets....
"DID you INSTALL the output transistors and turn it on ?????????????"
No .....
"The data you posted shows that the old and new (reverse installed) drivers test ok, but what happened after you installed the drivers correctly that led you to believe that the output transistors would survive after you installed them and powered them up?"
Before I reinstalled those 4 , I pulled every transistor and tested them . ( luckily I left a long enough " tail " on them , on the foil side ) . To my dis-belief they all checked ok . I proceeded to re-install them and re-flowed every solder point on that board . I then went over the board with a magnifying glass to make sure I didn't build any solder bridges to nowhere ( some of the traces were really close to each other ) . I said a little prayer , turned the unit on .... no magic smoke and a nice healthy "click" . I did a little happy dance and shut her off . I then set up to adjust the bias . After dialing that in , I hooked up some garbage speakers and watched it run for a bit on my bench , just to make sure everything was kosher and nothing was getting outrageously hot .
"You're either more skilled than you let on and really didn't need me, or lucky as the devil."
I would like to think a little of both. But i'm leaning 'twards the latter :stupid: And I would have gotten nowhere without your help . I can not tell you how much I appreciate all the help and time you provided me .
SolutionRoom
...***...
So is the thing working as advertised and all adjustments made??? I am confuzed as hell.... Is this a done deal? The suspense is killing me!
Maron
Always Learning
Done deal !!! 
I believe I made all the necessary adjustments . I set VR1,2 to 0 and VR3,4 to 20mV .
Sounds better than I can remember ( although it has been a few years). I never realized how long it took for that protection relay to click off before , when you first powered her up . It's comes on pretty fast now .
So , I believe its fixed , I'm listening to re-mastered Niel Young as I type . Are there any other Adjustments that need to be made ? Or anything else I need to test ?
I believe I made all the necessary adjustments . I set VR1,2 to 0 and VR3,4 to 20mV .
Sounds better than I can remember ( although it has been a few years). I never realized how long it took for that protection relay to click off before , when you first powered her up . It's comes on pretty fast now .
So , I believe its fixed , I'm listening to re-mastered Niel Young as I type . Are there any other Adjustments that need to be made ? Or anything else I need to test ?
A series of misunderstandings on my part happened, and I posted some inexcusable things here. I apologize to anyone and everyone that read them for sending those words out. They were entirely undeserved and totally in error.
You DID take measurements and found clues as to what were correct readings
and recognized it was safe to install the output transistors.
You EARNED A GREAT DEAL OF RESPECT FROM ME.
and recognized it was safe to install the output transistors.
You EARNED A GREAT DEAL OF RESPECT FROM ME.
