CurtPalme.com Home Theater Forum

Rattanee · Joined: 18 Jan 2015 Posts: 193

So I was watching Alien and Aliens tonight with some friends, and hit a problem... Using a HTPC as a source, direct into the PJ. Before the first film, I noticed that when Media Player Classic was open, where the bottom portion of the window was with the start, pause etc buttons, the white part, the left and right edges of the image 'bubbled' outwards slightly... It seems that the width of the picture varies with the brightness of what is displayed, but it does not affect the entire height of the image, the 'blooming/bubbling of the sides' only occurs at the precise height where white is displayed in larger quantities...
Some hours later, near the end of Aliens (probably about 4 hours since the PJ was turned on), it turned off... turning it back on, I lost red convergence... soon followed by an actual short of the convergence IC that then stopped the machine with F8. I replaced the convergence board with a spare, and everything's back to normal, but the 'blooming' is still present... I'm sorta afraid that it was the cause of the convergence board going (I've had the set on for much longer in one session earlier with no problems).
The PJ has had every single capacitor replaced about a year ago... so it's probably not a leaking caps thing, unless one of the new caps gave up... Any chance someone had a similar problem fixed?

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

It is a HVPS stability issue: where there is need for high anode current (white portion) the HV drops a little, causing horizontal width ~~shrinking~~ EDIT: growing. Now why is this happening is a very good question.

I know that your plain PG-s have two different type of HVPS, one with a switch, and the other without a switch. The switch is for setting the maximal anode current. I believe the HVPS without the switch is an older design, because all later NEC had not one but two shitches -it was that machine, without HVPS switch doing the problem?

Rattanee · Joined: 18 Jan 2015 Posts: 193

It's actually the reverse! Where there is white, the h-width increases! Maybe it's the deflection power that rises with anode current? It would make sense, higher power to the coils=more deflection... I will take some pictures to show what I mean...

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

Rattanee · Joined: 18 Jan 2015 Posts: 193

So here's a few pictures... It's misconverged (didn't do anything to it since replacing the C-drive board) I know, but you can see the problem. Wherever there's a white or near-white area, the outer edges 'bend'... this is not very apparent unless the white part is over half the total width of the projected image... Possibly related, I've had the image flicker for a fraction of a second a few times when I turned the set on today to snap these pictures... there were no sounds of HV arcing...

You mean the board standing vertically in the rear corner of the chassis opposite the two flybacks right? I don't think I've seen a switch on either of those when they were out of the set... where would it be located?

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

Yes, that's it, most CRT tv's did that too. HV instability.

Rattanee · Joined: 18 Jan 2015 Posts: 193

Would that be a capacitor that failed prematurely, or should I start looking at everything in the HV section?

Here's a 'before the fun started' pic.

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

Well, you have to find out if this is a constructional preblem or a you have a failing part.
The problem is the HV power supply does not regulate the HV well, so when there is a great demand (white portion) it can not keep up.
Now as I think about it, it even can be a bem limiting issue too, so the GAIN CTL or VIDEO OUT does not trips when too much current is flowing and the HV supply is simply overloaded...
You shuld start to swap boards Smile

Rattanee · Joined: 18 Jan 2015 Posts: 193

Jolly good... Time to go to my workshop and grab the second PG then... :\ Or wait... the plus parts should be backwards compatible right? I might just pull the boards from the tubeless plus and see how it goes Smile

**Curt Palme** · Posted: Sun Jan 31, 2016 4:18 pm Post subject:

The HV section on any NEC is matched between the HV transformer, splitter and HV board. You can try to mix and match from another set, but if the HV is off, the set will shut down prematurely.. or not soon enough. I'd recap the entire HV board and LV power supply and see if that makes it better.

Rattanee · Joined: 18 Jan 2015 Posts: 193

I've swapped the HVps between the two PGs before, and they work with each other. Thing is, I'll need to pull the set from the ceiling... I'll most likely swap tubes in the plus first and mount that in place while I work on this... Might as well mount the new struts I want to add...
Both have already been recapped Curt, if it's a cap failure, it's one of the new ones going down prematurely...

**Curt Palme** · Posted: Sun Jan 31, 2016 4:55 pm Post subject:

I've had that happen, depending on where you got the caps from. At least two local suppliers here sell cheap Chinese caps, and I've had them fail within 2 years. One in fact was a TV that I gave to an ex g/f, having recapped the supply, and it died within 2 weeks. I measured the bag of 30 caps I bought from them, and about 80% were way off spec. I now only buy from Digikey or Mouser.

Rattanee · Joined: 18 Jan 2015 Posts: 193

Time to dig out the scope I guess... If it's a problem with the supply feeding the HVPS, it should show a repetitive pattern with a fixed image... It's damn annoying that I've not had the beast on the ceiling for more then a year and now I have to pull it back down to troubleshoot Sad

**Curt Palme** · Posted: Sun Jan 31, 2016 5:34 pm Post subject:

Well, that's why I've stopped servicing them, far too many issues with them starting about 5 years ago. It's too bad, as otherwise they throw a really nice image, but with the chassis being 23+ years old at this point, it's pretty much to be expected.