MS2931 going into protection
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MS2931 going into protection
As the title states, I have an MS2931 going into shutdown immediately after power up.
No neck glow and no HV. Potting compound on H.Drive coil had leaked, but I removed the HOT, coil, and FBT and cleaned that up. With FBT and F701 removed, and HOT/coil installed, I've wired a lamp holder to the metal frame and PSU side of F701; 75W bulb does light up for a second or two.
HOT tests fine out of circuit.
R511 replaced since it had come into contact with the potting compound.
B+ is steady around 183VDC.
Vertical IC was replaced, showing 15VDC on pin 7, and 15VDC on pin 4; pins 5/6 show nothing (not sure if this is normal, absent an input signal), but I do read -15VDC from T901.
U921/U922/U602 are outputting steady 12VDC/5VDC/9VDC.
U951 pin 6 and U351 pin 26 both stay low; VCC reads 12VDC and 5VDC, respectively.
U901 pin 10 reads about 26VDC, and pin 7 reads 5V after shut down.
Heater reads around -10 to -11VDC, and even after 30 minutes the heater circuit hasn't drained. not sure if this is normal.
Haven't pulled Q901 and checked that, but I figured if all of my output voltages were good I shouldn't need to?
Not sure what to check, now. Any suggestions?
No neck glow and no HV. Potting compound on H.Drive coil had leaked, but I removed the HOT, coil, and FBT and cleaned that up. With FBT and F701 removed, and HOT/coil installed, I've wired a lamp holder to the metal frame and PSU side of F701; 75W bulb does light up for a second or two.
HOT tests fine out of circuit.
R511 replaced since it had come into contact with the potting compound.
B+ is steady around 183VDC.
Vertical IC was replaced, showing 15VDC on pin 7, and 15VDC on pin 4; pins 5/6 show nothing (not sure if this is normal, absent an input signal), but I do read -15VDC from T901.
U921/U922/U602 are outputting steady 12VDC/5VDC/9VDC.
U951 pin 6 and U351 pin 26 both stay low; VCC reads 12VDC and 5VDC, respectively.
U901 pin 10 reads about 26VDC, and pin 7 reads 5V after shut down.
Heater reads around -10 to -11VDC, and even after 30 minutes the heater circuit hasn't drained. not sure if this is normal.
Haven't pulled Q901 and checked that, but I figured if all of my output voltages were good I shouldn't need to?
Not sure what to check, now. Any suggestions?
- mufunyo
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Re: MS2931 going into protection
Have you run the tube through a tube tester?
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Re: MS2931 going into protection
the tube is fine, I have another 2931 that works just fine on it.
the chassis goes into shutdown on my test bench not connected to the tube.
the chassis goes into shutdown on my test bench not connected to the tube.
- mufunyo
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Re: MS2931 going into protection
Alright, I'll leave it to the experts then
- grantspain
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Re: MS2931 going into protection
have you check q701 and u701
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Re: MS2931 going into protection
I'll pull q701 when I get home tonight and check it.grantspain wrote:have you check q701 and u701
what am I looking for on u701?
- grantspain
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Re: MS2931 going into protection
q701 is something to do with hv regulation and controls the hv protection circuit i believe
i had that on one chassis once cause me a similar fault
the fact you have solid psu voltages and look to have an ok deflection circuit points towards the issue being hv regulation-but these are complex chassis so nothing is straightforwards with these
i had that on one chassis once cause me a similar fault
the fact you have solid psu voltages and look to have an ok deflection circuit points towards the issue being hv regulation-but these are complex chassis so nothing is straightforwards with these
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Re: MS2931 going into protection
do you recall if F701 was blown on that chassis? mine is still good, but was just curious.grantspain wrote:q701 is something to do with hv regulation and controls the hv protection circuit i believe
i had that on one chassis once cause me a similar fault
the fact you have solid psu voltages and look to have an ok deflection circuit points towards the issue being hv regulation-but these are complex chassis so nothing is straightforwards with these
I was wondering if I should see the trigger pulse on pin 1 of u701 or is it shutting down before it reaches that point?
- grantspain
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Re: MS2931 going into protection
no fuse was fine on my chassis,i am not sure what signal you would expect to see on the ic
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Re: MS2931 going into protection
q701 might be bad but I'm not sure. - on source, + on gate and move it to drain briefly shows a reading but then it goes out of range almost immediately. I don't have a variable PSU so I can't apply a higher voltage than what can be supplied by my DMM.
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Re: MS2931 going into protection
what?Rafaelsic wrote:I know the feeling. I was sure that it was going to be a hard to find wiring problem the first time, and was quite surprised to find out it was a 30 fix.