View Full Version : Runco 980 / NEC 6PG high voltage snap crackle pop


maxhifi
12-07-2016, 01:10 PM
My main TV isn't a TV at all, but rather a Runco CRT HDTV projector. Have had it installed for almost 12 years, with a few reliability issues.

1. Convergence amplifier failure required replacement of STK amplifier modules twice. (2012 and 2013)

2. Runco line doubler had bad solders on power transformer, this created reliability issues and needed repair (about 2008)

Now it has a new issue. While it's operating I can hear periodic high voltage arcing happening, as though insulation is breaking down. This sound is very familiar to me having worked on old tube type TV sets.

Inside the projector is an over complex mess of wiring and circuit boards, with a lot of status indicator LEDs and stuff which make it impossible to view the high voltage wiring in total darkness.

Attached is the schematic for the high voltage wiring. Note the use of two flybacks in parallel, and the large amount of high voltage connection points.

Any assistance in how to troubleshoot this problem would be greatly appreciated, as well as some direction on where to get spare parts. If it needs a new flyback or something I am lost as to where to find it.

At the moment there are no issues with the picture.

Electronic M
12-07-2016, 01:33 PM
I'd try cleaning everything in 6" of the HV with rubbing alcohol as a starting point...May just be a build up of conductive dust/dirt.

maxhifi
12-07-2016, 01:38 PM
I'd try cleaning everything in 6" of the HV with rubbing alcohol as a starting point...May just be a build up of conductive dust/dirt.

Good idea, will give it a try. given the age And the number of fans in this thing it can't hurt. It's i a clean dedicated room, but it's been there a while.

zeno
12-07-2016, 06:35 PM
Most likely thing is a cracked divider where the 3 anode
leads are. Give it a visual and also the FBT towers.
Since this is industrial & VERY expensive new there
may still be parts around.

73 Zeno:smoke:
LFOD !

maxhifi
12-07-2016, 06:41 PM
Most likely thing is a cracked divider where the 3 anode
leads are. Give it a visual and also the FBT towers.
Since this is industrial & VERY expensive new there
may still be parts around.

73 Zeno:smoke:
LFOD !

Thanks Zeno

That makes sense, the arcing sounds very very similar to when my 16" Zenith hybrid had a cracked focus divider. This one appears to be a reference voltage feeding back to the flyback drive circuit, the G2 voltage is taken from a tap on the flyback.

Agreed this thing cost a fortune, was part of a custom installation at my grandparents place when new.. they crated it up and sent it to me when they got too old to keep the house.

There's a guy on eBay who says he has parts for NEC projectors, I sent him a message to see what he's got for mine... short of that I will find a parts unit, I'm determined to keep it going

maxhifi
12-07-2016, 08:09 PM
Here's a peek inside. The flybacks are in the metal box.

Electronic M
12-07-2016, 10:36 PM
Another thing you can do is get some flexible rubber/plastic hose and make your self an HV stethoscope...

maxhifi
12-08-2016, 01:48 AM
Another thing you can do is get some flexible rubber/plastic hose and make your self an HV stethoscope...

That's an awesome idea. I am pretty sure I have some in the garage which I used for listening for bad bearings in cars.

I cleaned up the divider a bit, I can't see any cracks, but when I put my high voltage probe close to the divider I can hear static like sounds.

After cleaning it up a bit the sound seems almost gone.

The response I got from the vendor I contacted was he no longer stocks NEC parts due to most of them having bad caps by now.

zeno
12-08-2016, 09:33 AM
If you get a grounded screw driver around any hole
it will draw a full arc. Using meter wont as a rule.
Also a humdid day will make it arc.
For cleaning 91% isopropyl alcohol is dirt cheap &
evaporates fast with no residue. Also great for VCR
& audio heads & paths. BUT rumored to harm some CD lenses.

good luck
73 Zeno:smoke:
LFOD !

BTW that divider may be used in regular projo sets from other
makers too !

maxhifi
12-08-2016, 11:22 AM
I checked all around the divider and high voltage wiring with a grounded alligator clip lead, it made static like sounds everywhere but no arc. The noise is a lot less/nearly gone after removing and re-seating the boots and cleaning it. The divider is a murata part, I was wondering if I could find similar in a normal projection set. I'm. Unfortunately not one of those guys who picks up old sets and parts them out... but I am going to look through service data for a cross reference. The divider is sure remenice of a distributor cap in a car!

I will continue using the projector and see if it comes back after it's really warmed up. Given the advice I received I feel it may be prudent to Keep eyes open for a newer projector, re-capping this thing would be a real challenge. I don't feel the family would appreciate the 120" screen being replaced by my 1968 works in a drawer but that is the other option :)

macgyver655
12-26-2016, 10:06 AM
I have a bunch of boards for a PG. All internals pulled from a working set. Let me know if you need anything.

maxhifi
12-26-2016, 10:37 AM
Thank you!

I don't need anything now, but may in the future. The convergence board in these isn't too reliable. Let me think about it a bit, there's probably a few things I could use.