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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun May 09, 2010 4:49 pm Post subject: |
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| Curt Palme wrote: | It's a throwaway. There's a short in the potted section that has blown the MOSFETS.
You might be the first, but I've never had a SPellman HVPS that has blown the MOSFETS that doesn't also have a problem in the potted section, causing the MOSFETS to blow in the first place. |
Interesting you would say this Curt since the mosfets are on the hot side of the transformer and the potted section is the cold side. Now unless the transformer is shorted they are isolated from each other. And other then OVP and FB there is no connection between the potted and unpotted section.
Now unless there was an arc over at the transformer. And I will never say never, lol.
Are those mosfets IRFP450's?
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chillman
Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun May 09, 2010 7:27 pm Post subject: |
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Hmmm. was that the number on the old device or did you cross it to this one?
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chillman
Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria
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| Posted: Sun May 09, 2010 7:38 pm Post subject: |
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It is the number on the defective part. I think the HVPS is a newer version, as it also has the newer resistors (not the carbon ones) Here's a pic of the MOSFET:
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun May 09, 2010 7:51 pm Post subject: |
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Interesting. I'm looking at 2 different Marquee HV prints and neither one calls for a mosfet with that much current handling. What are the numbers on your supply case?
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun May 09, 2010 8:00 pm Post subject: |
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Nope. I'm looking at a Marquee HVPS print and is has those IRFP's and another Marquee print I have shows STH15NA50FI's.
I usually dont make mistakes like that.
Yes I had no problem seeing the ones he linked and I also looked at the datasheet. I'm curious if this is a different supply then the prints I have or if someone has been in there before.
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chillman
Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria
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| Posted: Sun May 09, 2010 8:01 pm Post subject: |
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I should have checked that link with my cache deleted...
Here's a pic of the labels on the HVPS:
Not sure if the 20/04 means it's from 2004?
EDIT: The solder joints did not look like these were replaced.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun May 09, 2010 8:06 pm Post subject: |
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Yeah, thats a 2532. I dont have the print on that one.
Well looks like your shooting from the hip on that one.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun May 09, 2010 8:07 pm Post subject: |
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How are they testing that you know they are bad?
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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chillman
Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria
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| Posted: Sun May 09, 2010 8:13 pm Post subject: |
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@mcgyver: Zero resistance between any of the pins.
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Sun May 09, 2010 10:46 pm Post subject: |
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| Curt Palme wrote: | | Put it in a set and put your ear to the case of the HVPS. If you hear a ticking sound, it's a writeoff. If it's dead without the ticking, there's about a 1 in 3 chance it can be repaired. I've gotten a few running. |
Yep, if it's "clicking" trash it...
The clicking usually means a load or excessive load on the secondary of the transformer. That would be the diode/capacitor multiplier section (potted).
The first HVPS had a higher failure in that section. Some would even spew out a brown substance from the potted material when they went bad.
The later versions used some different components (diodes) in the design. I used to have the part numbers.
Because of the over voltage control (OVP) circuits used in these supplies, you would need the exact parts. Also when one diode goes, one of the other diodes could also be effected from it shorting out. That's more of the reason to write it off.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Tue May 11, 2010 12:02 am Post subject: |
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Like any switching power supply there are safe ways to test operation. First involves powering up the low voltage control section without the B+ (385VDC). At this point check the drive to the output mosfets for proper frequency and voltage. If all is well bring the B+ up a couple of volts and monitor the drive going into the flyback transformer and the output voltage. If there is a problem with the transformer or the multiplier there will be a distortion on the flyback drive. If all is well bring the B+ up more. Continue increasing the B+ until the output reaches the correct level. At that point the duty cycle of the mosfet drive will begin to decrease to maintain the output voltage as the B+ increases.
All it takes is the proper equipment, training, schematics, circuit parameters, yada, yada.........
Even stuff in the potted section can be repaired. I've seen Ampro Spellmans that had chunks of the potting removed and replaced. The Marquee Spellmans are very similar. They can be repaired, too.
Using your projector as a test fixture can be a bad idea. I once saw a prototype HV supply turned on in a projector and all was well for 10 or 20 seconds when the picture suddenly got real small and bright. That lasted for about two seconds then the HV arced THROUGH the neck of the tube to the clamp on the yoke. I guess the HV output went up to like 100kV before the arc.
We used to use a HV triode (6BK4) load bank for testing HV supplies. The output current could be set from nothing to 3 or 4 milliamps to set current limit, overvoltage shutdown, and transient response. The tubes were inside a lead lined box to cut down on the X-Rays. Yeehaw!
Scott
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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| Posted: Tue May 11, 2010 1:29 am Post subject: |
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| tse wrote: | Like any switching power supply there are safe ways to test operation. First involves powering up the low voltage control section without the B+ (385VDC). At this point check the drive to the output mosfets for proper frequency and voltage. If all is well bring the B+ up a couple of volts and monitor the drive going into the flyback transformer and the output voltage. If there is a problem with the transformer or the multiplier there will be a distortion on the flyback drive. If all is well bring the B+ up more. Continue increasing the B+ until the output reaches the correct level. At that point the duty cycle of the mosfet drive will begin to decrease to maintain the output voltage as the B+ increases.
All it takes is the proper equipment, training, schematics, circuit parameters, yada, yada.........
Even stuff in the potted section can be repaired. I've seen Ampro Spellmans that had chunks of the potting removed and replaced. The Marquee Spellmans are very similar. They can be repaired, too.
Using your projector as a test fixture can be a bad idea. I once saw a prototype HV supply turned on in a projector and all was well for 10 or 20 seconds when the picture suddenly got real small and bright. That lasted for about two seconds then the HV arced THROUGH the neck of the tube to the clamp on the yoke. I guess the HV output went up to like 100kV before the arc.
We used to use a HV triode (6BK4) load bank for testing HV supplies. The output current could be set from nothing to 3 or 4 milliamps to set current limit, overvoltage shutdown, and transient response. The tubes were inside a lead lined box to cut down on the X-Rays. Yeehaw!
Scott |
Scott, your NUTS!!!! 
Nashou
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Tue May 11, 2010 1:48 am Post subject: |
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Oh C'mon, why not take a risk trying to repair a HVPS? Heck, Tim called me today, saying that he was about 15 seconds and 3" from being fried by a bad Marquee HV lead, that arced like mad shortly after he got his fingers out of the set...yikes!
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue May 11, 2010 1:52 am Post subject: |
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See. And you guys thought I was kidding when I said to have your gloves, goggles and fire extinguisher handy.... 
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Tue May 11, 2010 1:53 am Post subject: |
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| macgyver655 wrote: | | See. And you guys thought I was kidding when I said to have your gloves, goggles and fire extinguisher handy.... |
and the faraday cage?
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chillman
Joined: 09 Apr 2007
Posts: 134
Location: Germany, Bavaria
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| Posted: Thu May 27, 2010 6:42 pm Post subject: |
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Hi everyone,
As I already said in the other thread, my spare HVPS died too. (clearly a failure in the potted section)
Being a bit frustrated I then took the MOSFETs out of the spare HVPS (STH15NA50FI) and soldered them into the
one that failed earlier.
I didn't have much hope as these aren't even the same MOSFETs, but I just powered on the Marquee and it worked!
So nothing wrong in the potted section, I guess.
So now I'll order the right MOSFETs as I don't think the older type will work permanently in the 2004 HVPS.
I'm very happy as I wouldn't have been able to buy a new HVPS at the moment!
Greetings!
Tillman
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