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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: Sun Nov 13, 2011 12:59 am Post subject: Ooops! |
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From a customer:
I’m reading 7.9 volts on the p14 in standby mode, 13.2 volts when it’s powered up. Am I screwed?
Does anyone know if that trimpot opens on a LVPS, how high the voltage can go? 13.2 is way way more than I ever measured...
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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 Nov 13, 2011 1:30 am Post subject: |
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I believe +13.5 would be the maximum capability of that circuit.
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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: Sun Nov 13, 2011 2:22 am Post subject: |
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I've linked him to this thread, and have indeed told him to try another meter.
It's actually an 8000, so the only way it can have a bad LVPS is if the original went bad and a later series got swapped in.
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Tim in Phoenix
Joined: 21 Oct 2006
Posts: 4409
Location: Phoenix
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| Posted: Sun Nov 13, 2011 2:40 am Post subject: |
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I have seen eleven volts on an 8500; that was the Brightest 8500 you ever saw! (for a few hours anyway)
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Sun Nov 13, 2011 5:22 pm Post subject: |
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yes it can go up over 12 volts from what I recall. That's why the original circuit was such a design screw-up. Your trying to dial in exactly 6.35 with a 20 turn pot on a 12+ volt circuit. So you get .6 volts per turn which is too coarse to start with
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun Nov 13, 2011 5:35 pm Post subject: |
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I believe one of the designs called for a regulator in that pot location. Surely would of been more stable.
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Sun Nov 13, 2011 11:06 pm Post subject: |
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the later "Ultra" power supply's did have what I believe is a small regulator circuit of some sort? IT's a little daughter board and it's still not perfect although the voltage is consistent and safe at 6.23VDC on every one I checked.
The best solution IMO that an EE at work came up for me is resistor which drops overall circuit down to 8VDC and then a new 20 turn pot which allows an exact and very stable 6.35.
Funny thing is the video-philes here are a lot more anal about that spec. than electrohome or VDC ever was. 
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun Nov 13, 2011 11:15 pm Post subject: |
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| draganm wrote: | the later "Ultra" power supply's did have what I believe is a small regulator circuit of some sort? IT's a little daughter board and it's still not perfect although the voltage is consistent and safe at 6.23VDC on every one I checked.
The best solution IMO that an EE at work came up for me is resistor which drops overall circuit down to 8VDC and then a new 20 turn pot which allows an exact and very stable 6.35.
Funny thing is the video-philes here are a lot more anal about that spec. than electrohome or VDC ever was. |
This was not a daughter board. The regulator went right where the pot is. This was suppose to be on 01/02 power supplies. Of course I dont know if any went into production that way or if it was changed to the pot design before production. but it was in the original design for that production year or later.
Any pot design can drift but a regulator design can also fail. Funny how Marquees only have this filament issue though.
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sun Nov 13, 2011 11:58 pm Post subject: |
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I've never even looked at what controls or regulates that on a AmPro. I just never felt it might be a issue. Not sure about Sony's but I don't think it ever was a issue with NEC.
Barco's can burn up for all I care  Where's Pete when I feel like bustin balls. 
_________________
Chip
A Barco is only a AmPro with training wheels
Card carrying member of the AVS chain gang.
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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: Mon Nov 14, 2011 12:14 am Post subject: |
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THe Ampros do have a filament control on one of th ePC boards. You could access it via the rear vent slots on the old 2000, so I boosted the filament on the one I had back in 1999 to 7 volts as the tubes got a bit old.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Nov 14, 2011 12:22 am Post subject: |
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Fil comes from the horz supply (HOT) board in newer Ampro's. All electronic, non adjustable.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Mon Nov 14, 2011 12:35 am Post subject: |
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You guys are way off on this one. The Ampro projectors always had a regulator in the LVPS where the output voltage was set with two fixed resistors. The CRT manufacturers spec for fil voltage was wide enough that there was no need for a pot. How such a simple thing got so screwed up in the Marquee is a mystery to me.
Scott
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"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Nov 14, 2011 12:40 am Post subject: |
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| tse wrote: | You guys are way off on this one. The Ampro projectors always had a regulator in the LVPS where the output voltage was set with two fixed resistors. The CRT manufacturers spec for fil voltage was wide enough that there was no need for a pot. How such a simple thing got so screwed up in the Marquee is a mystery to me.
Scott |
I found my info in the 3600/4600 schematics. It shows filament in print. I'm going to look at the LVPS prints now.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Nov 14, 2011 12:46 am Post subject: |
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Yes, I see the fil supply in the LVPS. Whats with the fil circuit in the horz supply?
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Nov 14, 2011 12:48 am Post subject: |
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Don't tell me they used fil supply for horz centering...... 
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Mon Nov 14, 2011 4:03 pm Post subject: |
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| macgyver655 wrote: | | Don't tell me they used fil supply for horz centering...... |
Well, yeah. There is a reason that that is bad. Do you know why?
It looks like the later Maquee LVPS didn't use a pot to set the filament voltage. The regulator has about 13.5V applied so worst case regulator short could put that much on the CRT heater. That couldn't be good.
Scott
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"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Nov 14, 2011 4:19 pm Post subject: |
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| tse wrote: | | macgyver655 wrote: | | Don't tell me they used fil supply for horz centering...... |
Well, yeah. There is a reason that that is bad. Do you know why?
It looks like the later Maquee LVPS didn't use a pot to set the filament voltage. The regulator has about 13.5V applied so worst case regulator short could put that much on the CRT heater. That couldn't be good.
Scott |
I could think of a couple reasons why its bad and I may have had one some years back. But I want to check my notes to see if my issue was from this circuit. I'll be back there in a week. I know the problem part was on a horz board but was not a horz issue.
That Marquee image is the one I was referring to in my earlier post.
So give me your reason. 
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Mon Nov 14, 2011 5:37 pm Post subject: |
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The filament rail is floating coming out of the LVPS. It then connects to the horizontal winding of the deflection yokes. The DC voltage applied to the h winding goes from about 20V to over 200V over the sweep range 15-105kHz. That means the filaments in the CRTs can be referenced 20 to 200V above ground. The CRT spec allows the cathode to be something like 300V more positive than the filaments but 0V negative relative to the filaments. That can be violated at the highest sweep rates. One (of many) good reasons not to run an Ampro above 80 or 90kHz.
Scott
_________________
"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Nov 14, 2011 7:09 pm Post subject: |
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| tse wrote: | The filament rail is floating coming out of the LVPS. It then connects to the horizontal winding of the deflection yokes. The DC voltage applied to the h winding goes from about 20V to over 200V over the sweep range 15-105kHz. That means the filaments in the CRTs can be referenced 20 to 200V above ground. The CRT spec allows the cathode to be something like 300V more positive than the filaments but 0V negative relative to the filaments. That can be violated at the highest sweep rates. One (of many) good reasons not to run an Ampro above 80 or 90kHz.
Scott |
Wow, didn't see that until looking at the horz out diagram. Also, a short failure of CR1 on the horz power board and the horz winding is tied directly to the filament supply......and heater.... 
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