CurtPalme.com Home Theater Forum

Daddy · Joined: 16 Jul 2010 Posts: 13 Location: Netherlands

When modifying a BG808s retro into a front pj I forgot to put the HV lead back into the splitter Shocked

.
When I swithed the set on I heard the sound of a big spark (!) and then the set went dead.
After I plugged the HV lead into the splitter and switched on again all seemed to work well in that there are no red leds anywhere. The system responds to the remote (i.e. I can switch it on and off), the fans are turning, all lights on the SMPS are green, the HV is up and non of the video board shows a red led, the neck boards have their green led on, ...).

But.... the only thing that happens is that the green tube lights up extremely (!) bright (but exactly within the grid dimensions) and the blue and red tube do nothing. Only the switch off key on the remote has any effect.
I then feel compelled to switch off the system within seconds not to burn the green tube.

I checked and rechecked all the wiring and all seems well. Although I unplugged all wires in the process of converting from back to front projector I am confident I did not make mistakes in reconnecting all the wires.

Has anybody made the same horrific mistake and was able to salvage the pj? How?
Or just based on the symptons.... any ideas where/how to start repairing my pj?

I do not have a service manual and could not find one on this site or elsewhere on the internet.
Does anyone of you have a PDF version of the service manual that I could download?
It will likely help me do some metering and further analysis.

Many thanks for any and all responses.

Ben851 · Joined: 13 Sep 2008 Posts: 221 Location: Ottawa, Ontario

Disclaimer: I'm no expert on these things. Curt will have a better answer.

I would expect that you've fried your HVPS or maybe if you're lucky, just the splitter.

The main reason I'm posting is to say you probably shouldn't cycle it on anymore until you hear from one of the more advanced members - you could run the risk of permanently damaging the tubes (spot burn or otherwise).

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Pull the Green neck board and check the CRT pins and connections. Was it working fine before ?

**Curt Palme** · Posted: Fri Aug 20, 2010 2:23 pm Post subject:

Nope, I think you're OK so far.

First off, the WORST thing you can do is switch off the projector when a tube is super bright. Fortunately you had a Barco, and spot burns are very rare (although I had a bad 1208 neck board do it once). Best you can do is either wait for the HVPS overcurrent sensor to kick in, which shuts down the HV safely, or leave the set on and pull out the EHT board. Running the tube at max current for say 30 seconds to a minute or so won't hurt the phosphor.

Now, the problem you have is with the green tube. As tom said, I'll bet a pin has bent over while putting on the neck board. If not, leave the green neck board off the set and see if the R and B will fire up with the green disconnected. Swap the green neck board with the red as Tom suggested also.

Daddy · Joined: 16 Jul 2010 Posts: 13 Location: Netherlands

**Curt Palme** · Posted: Fri Aug 20, 2010 2:30 pm Post subject:

See my post above. Smile

Tom.W · Joined: 09 Mar 2006 Posts: 6635

You could try swapping neck boards to to see if the trouble moves with the swap but it sounds like a bad video amplifier on the green neck board.

Looks like I missed your post Curt...

**Curt Palme** · Posted: Fri Aug 20, 2010 2:41 pm Post subject:

If it's the 120 Mhz neck boards with the amp and heatsink on the socket, those are usually pretty reliable. If it's the video amp that's bolted to the chassis.. those can indeed fail and give a massively bright screen with no video.

Daddy · Joined: 16 Jul 2010 Posts: 13 Location: Netherlands

Thanks for all the suggestions.

I just swapped the neckboards. The problem stays with the overbright green tube.
The neckboards have indeed a big heatsink and I believe they are 120 MHz (no idea how to check..)
There are two sets of wire harnasses attached to the neckboards. One set a.o. provides current to the fillament.
No idea what the other set is doing.

Anyway... as it appears the probl;em is not with the neck board.
What else can I check?

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Read this on CRT failures...

http://repairfaq.cis.upenn.edu/sam/reppic/sencrt.pdf

The bad news is you could have a heater to cathode short in the CRT. You can check for this with an ohmmeter.

jkruger · Joined: 24 Oct 2007 Posts: 2435 Location: Carlsbad, CA

Check the pins on the tube very carefully. I did this on an old sony years ago and it was difficult to see.

Daddy · Joined: 16 Jul 2010 Posts: 13 Location: Netherlands

To see if the problem is related to the actual tube I just swapped the green tube with the blue one.
But now the overbright problem is on the swapped tube so it seems the fault is somewhere in the green-signal-chain and is not tube related.

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Now there's a mystery. Any ideas Curt ?

**Curt Palme** · Posted: Fri Aug 20, 2010 3:47 pm Post subject:

Jumper pins 2 and 6 together, maybe the tubes are wired differently?

Daddy · Joined: 16 Jul 2010 Posts: 13 Location: Netherlands

Curt, not sure what you mean by tubes that are wired differently. Maybe my post was unclear.
To rule out that it was tube related I used another tube. But that other tube then also gets overly bright.

Also not sure what you mean by jumper pins 2 and 6. Where are they located and what could be wrong with them?

I meanwhile bought a softcopy 808s service manual for $7.
Browsing through it made me think that perhaps it is the convergence module that is in the lid above the motherboard. According to the service manual here are the amplifiers that drive the red green and blue deflection coils. But there is no notion in the manual how to test the board or what voltages should be present.

**Curt Palme** · Posted: Fri Aug 20, 2010 4:21 pm Post subject:

Sorry, I read it as being an issue with the tube, not the tube location.

the problem is video related, it has nothing to do with the yokes or convergence.

I'd say your video output is bad. Swap the CRT sockets between tubes.

Daddy · Joined: 16 Jul 2010 Posts: 13 Location: Netherlands

OK, I once more swapped the CRT sockets (actually that implies swapping the neck cards as the socket is part of that assembly).
As the pins of the tube looked rather dark from oxidation I even used very fine sandpaper to brush up the pins a bit.
This does not help... the green tube remains fully bright on start-up.

Just to check how the other tubes are still doing I took out the HV of the green tube and started again. Unfortunately now the blue and red tubes remain dark, even when I press the ADJ button on the remote.

I checked the status leds again but no change at all, everything seems normal from that point of view. I also checked the wiring again as all this swapping might have caused one of those thin wires come loose. Again, all seems OK.

I hope you have some more ideas that I can exploit.
Does the fact that red and blue now remain dark even when I take out the green one say anything that point towards the fault?

Hope to hear from you, really appreciate your thoughts and ideas

**Curt Palme** · Posted: Fri Aug 20, 2010 8:04 pm Post subject:

No, at this point you should send me the green CRT neck board and the RGB switcher and quad decoder for testing. That would be my best guess where the problem is.

Daddy · Joined: 16 Jul 2010 Posts: 13 Location: Netherlands

One more observation and then I will stop bugging you with my Barco problems

After swapping the neckboards arround I found a configuration whereby red and green seem to work and blue needs to be off (or else blue lights up too bright and triggers the HV down).

By looking at the green tube I can access all the convengence and configuration settings. This gave me some hope that the PJ can be salvaged. However..... what seems discouraging is that the text on red and green are not in the same orientation. I.e. when green is in "ceiling-front" orientation red is in a different orientation setting. Does this sympton provide any extra clue?

Also is does matter which neckboad (they have a video amplifier as well) goes to which tube.

Or does this sound as if the PJ is beyond (economically justified) repair?

**Curt Palme** · Posted: Mon Aug 23, 2010 2:11 pm Post subject:

It can all be repaired, the problem is you're most likely now looking at a 'user created' fault rather than a naturally occurring failure in the set. A user created fault is always harder to solve than a standard component failure. You need to send me boards in order for me to check them.