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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Thu Sep 30, 2010 3:39 pm Post subject: Marquee LVPS 85 volt rail? |
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how critical is the 85 volt rail on a marquee. I measured one last night that was waivering between 86/87vdc and I'm thinking that's not a problem? Opinions?
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Tim in Phoenix
Joined: 21 Oct 2006
Posts: 4409
Location: Phoenix
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| Posted: Thu Sep 30, 2010 4:12 pm Post subject: |
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Hey
Mike Parker sez the neckboards want 85 volts precisely. Try another lvps.
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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: Thu Sep 30, 2010 5:02 pm Post subject: |
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The LVPS in the Marquee is very well regulated. It's rare that one would be off, and if off, there's a pot to adjust it to the exact 85vdc that it needs to supply.
Since that pot is not really accessible when the supply is in the set, and adjustment is not possible unless you have an extender for the LVPS. It would be best to just replace the LVPS.
Also, the pot for the 85vdc adjustment is the same manufacturer of the 6.3vdc pot for the filament voltage.
That rail is critical for two reasons. 1, it also supplies the 85vdc that drives the power FETS on the HDM. It's the main voltage for horizontal sweep.
2, it supplies both +/- 85 vdc for the neck boards. And it's also important for those rails to be accurate. Both (+85/-85) rails come from the secondary of a dedicated 85 volt switching transformer that supplies the 85 volt rails in the LVPS, so they would most likely measure the same voltage. if not something is seriously wrong either a load or problem in the LVPS.
What I've found to be acceptable is 84vdc measured with a good meter (Fluke). Anything much above that I would be concerned enough to replace the LVPS.
There's a small cap on the LVPS that's usually associated voltage drifting on the LVPS 85 vdc rails, but in this case, I think it would best to replace with another supply and not attempt to repair it yourself. Or you could send it to Curt for repair.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Fri Oct 01, 2010 12:35 pm Post subject: |
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Any change on the +/-85V rail will get into the video on the cathode and G-1. The neck card amps have very little power supply rejection ratio (PSRR).
Scott
_________________
"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Fri Oct 01, 2010 3:37 pm Post subject: |
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| mp20748 wrote: | | That rail is critical for two reasons. 1, it also supplies the 85vdc that drives the power FETS on the HDM. It's the main voltage for horizontal sweep.. |
thanks guys, this is the LVPS from that machine with the wierd horizontal Oscialltion we've been chasing now for weeks. 2 different HDMS, an 07 and an 08 both produced the same problem in this guys 9500 with short retrace. With this LVPS in my 8110 test mule I couldn't get the oscialltion to occur but the raster would jump up and down in short retrace only.
With my LVPS everything is steady and I measured 84.7 consistently. With the customers LVPS it would oscillate 86-87-86 etc. I really didn't think it was a problem so i'm glad I asked here on the forum.
| mp20748 wrote: | | Also, the pot for the 85vdc adjustment is the same manufacturer of the 6.3vdc pot for the filament voltage. . |
yeah i noticed that, the little gray trim pot labeled MEXICO. Looks Spellman was still using this circa 2000 even though the P14 circuit is the new daughter board style on this one.
| mp20748 wrote: | | There's a small cap on the LVPS that's usually associated voltage drifting on the LVPS 85 vdc rails, but in this case, I think it would best to replace with another supply and not attempt to repair it yourself. Or you could send it to Curt for repair. |
this unit has all Nichikon 105c hi-temp caps which i've never noticed before and they're stock with glue slopped all over. Admittedly I don't look inside many of these but the older ones use all Marcon's.
| tse wrote: | Any change on the +/-85V rail will get into the video on the cathode and G-1. The neck card amps have very little power supply rejection ratio (PSRR).
Scott |
thanks, I'm glad you suggested looking at PS , it's one thing I think is easy to take for granted
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Mon Oct 04, 2010 3:39 pm Post subject: |
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just wanted to add this for anyone needing help in the future. The trim pot for the 85 volt rail can be adjusted rather easilly as it's 1/2 turn of the pot for slightly less than 1/10th of a volt change, closer to like .18 volts per full turn. turn the pot in (clockwise) to DE-crease the voltage if your over 85VDC.
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