# Trouble Shooting MASTERS ? Solid state help...



## Darylbnet22 (May 9, 2007)

Hello All, We are trying to repair some old 120-150vdc power supply cards...
The problem is we can get the cards to work, but have an issue of spiking...
When at zero pot, the unit will stay at zero output, but will spike periodically, like every 30 seconds, some a minute or two...
We can see the firing network, slowly building voltage, till it saturates and causes the spike...
We only have one good board at this time, which works correctly, and doesn't spike, and ranges smoothly, when the pot is increased, to fire at 0vdc through to about 100vdc or 120vdc...
I will be posting any reference info I have to aid in this discussion...
We think it is a fault capacitor, allowing this to build and spike, but any assistance of what areas to focus on would be GREATLY appreciated...


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## Darylbnet22 (May 9, 2007)

Also, will be working at times, and will reply back when I get back in range, tks,,,


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## just the cowboy (Sep 4, 2013)

If you can't get it, send it to presion electronics repairs, they repair some old stuff for me. Send the prints it will help them if they don't have them.
http://www.pesquality.com/


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## Cow (Jan 16, 2008)

just the cowboy said:


> If you can't get it, send it to presion electronics repairs, they repair some old stuff for me. Send the prints it will help them if they don't have them.
> http://www.pesquality.com/


Thanks cowboy!

I filed that link away for future reference!:thumbup:


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## Darylbnet22 (May 9, 2007)

Maybe Bd has some insight on this issue...


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## MikeFL (Apr 16, 2016)

Some of those resistors look like they've taken some heat. Check their value vs the schematic value.


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## RePhase277 (Feb 5, 2008)

My guess is bad capacitor. The bases of the transistors are coupled to a supply rail via a capacitor. If the capacitor charges too quickly or slowly, or not at all, transistor firing will be affected.


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## OldMasterTech (Mar 12, 2014)

4397 date code shows 20th birthday but this was old technology even then so that may be a revision date.
Anyway step one is a visual for poor or overheated solder connections or components. To measure the overheated resistors unsolder one lead as other components in series or parallel will give you an erroneous reading.
Replace all the electrolytic capacitors, after 20 years I guaranty all of them have changed value or failed.
These things you can do in the field, if no success then it's benchtime.


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## Darylbnet22 (May 9, 2007)

THANKS, Mike, Rephase, and OMT, All good insight, and yes we have these on bench time t/s, and have been changing socket bases, and all removable transistors... 
We will check into the burden resistors more and all capacitors... 
We have 3 boards which do this same spiking issue, so we are thinking this should be a common cap fault...


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## splatz (May 23, 2015)

My standard uneducated guess is the capacitors. This is like guessing one or zero on a math test, I can't show any work because I have no idea but a lot of times the answer is one or zero, way more than the other numbers. 

Have others seen resistors fail in this kind of thing? I personally never really looked for that. Do they tend to fail open, closed, or just have the resistance change over time.


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## oliquir (Jan 13, 2011)

id also say capacitors, that is the only part that wear out with time . i would change all the Aluminum electrolytic one's


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## RePhase277 (Feb 5, 2008)

splatz said:


> My standard uneducated guess is the capacitors. This is like guessing one or zero on a math test, I can't show any work because I have no idea but a lot of times the answer is one or zero, way more than the other numbers.
> 
> Have others seen resistors fail in this kind of thing? I personally never really looked for that. Do they tend to fail open, closed, or just have the resistance change over time.


Resistors rarely fail unnoticed. When they fail, they usually burn in two or pop a hole in the side.


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## dmxtothemax (Jun 15, 2010)

Those circuit boards look pretty grotty !
Boards covered in dust dirt and what ever 
Can develop high impedance leaks
Which may explain why your capacitor slowly charges up
Have you tried cleaning the boards
Clean them in soapy water with a good grease cutting detergent
use a tooth brush on it to get to all area's
rinse 
allow to dry properly.


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## telsa (May 22, 2015)

Leave circuit boards to bench techs.

They've got both the gear and the mentality.


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## JRaef (Mar 23, 2009)

That looks to be an old 3 phase linear power supply. The description sounds like your pulse circuits are failing. Could be the caps, but it could also be the pulse transformers; i.e. the insulation is breaking down and the voltage for the pulses is low, so it's taking too long to build up in the caps resulting in some pulses firing at the wrong times.

The pulse transformers may not be available any more though, people stopped using that type of power supply a couple of decades ago, so component mfrs lose their market and move on. Might be time to update to a new Switch Mode Power Supply and get with the '90s...


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