SX 1250 stabilizer issue

rhodus

rhodus

AK Subscriber
Subscriber
Hey everyone! I'm finishing up a 1250 and I am stumped again. I'm not getting any voltage at pins 13 and 14. I do have the -87.5v at pin 15. The collectors of Q5,6 have 87.5v but there is no voltage at the emitter of Q5 or the base of Q6. The base/emitter junction of Q5,6 has no voltage. Q5 is a MJE15033 and Q6 is a KSA1013. I have replaced them again just in case but still nothing. Any help would be gladly appreciated.
 
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Q7 collector voltage comes from R2 2.7k charging c2 220uf and through R4 2.7k. This powers up the regulator circuit, supplying collector voltage for Q7, which lights off the Q5 and Q6 pass elements, Without it R6 is starved and does not supply voltage to D3 the zener diode which then with the feedback from the voltage divider causes Q7 to pull the rising voltage down to the regulated voltage.
 
markthefixer said:
Q7 collector voltage comes from R2 2.7k charging c2 220uf and through R4 2.7k. This powers up the regulator circuit, supplying collector voltage for Q7, which lights off the Q5 and Q6 pass elements, Without it R6 is starved and does not supply voltage to D3 the zener diode which then with the feedback from the voltage divider causes Q7 to pull the rising voltage down to the regulated voltage.
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Thanks Mark, I will be back on it this evening...
 
Got it down to D3 and replaced it with 1n5252b. The protect relay pulls in now but the voltage is now only -18 where it should be -66...still looking
 
Okay, I went through and replaced all diodes with new AND replaced again all other transistors after seeing that q7 was visibly blown. All pin voltages are now in spec EXCEPT for pins 13 and 11, which I cannot get above 61v on either one.
 
I have a non-restored stabilizer board from my donor carcass that I use for a reference and it works fine so I know the issue is somewhere on this board and not the rest of the unit....
 
My explanation of what caused all this: I started the unit with a 150 watt DBT. Unit Powered up, protect relay engaged, and after about 10 seconds,the relay disengaged and smoke appeared. Shut it down, removed stabilizer board and realized I had q12 in backwards. Replaced q12 and started this thread....I think 150 watt DBT might be too high? The other units I worked on I used 100 watt bulbs. Don't know if it would have made a difference
 
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Might be working, with DBT limiting voltage on pins 11 & 13, look at voltage for pins 6 & 15.

People don't understand DBT, higher wattage results in closer to normal voltages, yet hugely abnormal current draws of the smoke variety are strangled. And there is NO extra smoke because of it.
 
markthefixer said:
Might be working, with DBT limiting voltage on pins 11 & 13, look at voltage for pins 6 & 15.

People don't understand DBT, higher wattage results in closer to normal voltages, yet hugely abnormal current draws of the smoke variety are strangled. And there is NO extra smoke because of it.
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I am working on house power now. 6 and 15 are normal. Only 13 and 11 show low voltage.
 
Okay, here are my stabilizer voltages on house power
1- 73.1
2- 73.1
3- 0
4- 53.5
5- 53.5
6- 89.1
7- 24.4
8- 5.5
9- 13.6
10- 24.2
11- 61.2
12- 0
13- 61.2
14- 24.5
15- 90.5

The voltages on pins 13 and 11 are with vr1 and vr2 turn all the way up.
Again, my unrestored reference stabilizer board works fine.
 
rhodus said:
Okay, here are my stabilizer voltages on house power
1- 73.1
2- 73.1
3- 0
4- 53.5
5- 53.5
6- 89.1
7- 24.4
8- 5.5
9- 13.6
10- 24.2
11- 61.2
12- 0
13- 61.2
14- 24.5
15- 90.5

The voltages on pins 13 and 11 are with vr1 and vr2 turn all the way up.
Again, my unrestored reference stabilizer board works fine.
Click to expand...
 

Attachments

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markthefixer said:
Is Q3 a ksc1845 and Q7 a ksa992? And the trimpots 652-3386h-1-502lf?
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Yes, that is correct. I even removed the trimmers and checked their operation with an ohmmeter. I have also checked most but not all board resistors and have replaced again all capacitors. It seems a few resistors are all that's left.
 
rhodus said:
Yes, that is correct. I even removed the trimmers and checked their operation with an ohmmeter. I have also checked most but not all board resistors and have replaced again all capacitors. It seems a few resistors are all that's left.
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The foil side is in good shape and all solder pads good...
 
I'm looking at this, The +- regulated is acting the same. They are mirrored circuits and share nothing (An identical, wrong component installed on both sides?). Neither can adjust to the +-64v's needed. If was working correctly, you would be half way into the trimmers to achieve the +-65v's. Somewhere near 2,500 ohms.
You mentioned the trimmers, They are 5,000 ohm's? What about the zeners? D1 and D3? 24v's? Check the package and the diodes themselves, you'll need a magnifier. It wouldn't be the first time Mouser mislabeled component bags.
 
zebulon1 said:
I'm looking at this, The +- regulated is acting the same. They are mirrored circuits and share nothing (An identical, wrong component installed on both sides?). Neither can adjust to the +-64v's needed. If was working correctly, you would be half way into the trimmers to achieve the +-65v's. Somewhere near 2,500 ohms.
You mentioned the trimmers, They are 5,000 ohm's? What about the zeners? D1 and D3? 24v's? Check the package and the diodes themselves, you'll need a magnifier. It wouldn't be the first time Mouser mislabeled component bags.
Click to expand...
Thanks, I will get on that this evening
 
Problem solved. The trimmers were 501s instead of 502s. And it wasn't Mouser's fault, I had them incorrectly sorted in my organizer. When I checked with ohmmeter I was only concerned with operation and did not catch the improper value. Gonna check the trimmers on the amp boards now and move on to more testing. I will be posting results with pics. MANY THANKS!!
 
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