CurtPalme.com Home Theater Forum

winny

So I couldn't misd out on an $80 Graphics 808s when I have so many spare parts laying around.

Fire it up an everything is green except red light on V-board. Press ADJ and I can hear it changeing frequency.

All green. Neckboards, G2, no red EHT on and the controller is happy.

Any suggestions?

barclay66 · Posted: Tue Jun 16, 2015 8:44 pm Post subject:

Hi,

I'd check the fuse on the EHT board first. If it's blown, then replace with a new one (same rating as the original one). If it blows again, there might be a shorted Power MOSFET on the EHT or the quadrupler is dead...

Regards,
barclay66

winny · Posted: Tue Jun 16, 2015 8:52 pm Post subject:

Funny. You work as an electronic engineer and don't even have a multimeter at home. Rolling Eyes

I'll bring it to work and check it there.

Any compability issues if I swap one from my data 808s if it's also new style EHT?

winny · Posted: Tue Jun 16, 2015 9:10 pm Post subject:

My data 808s had old style EHT.

barclay66 · Posted: Tue Jun 16, 2015 10:09 pm Post subject:

Hi,

If the part numbers (R762...) are identical, You can swap them without hesitation...

Regards,
barclay66

winny · Posted: Wed Jun 17, 2015 8:23 am Post subject:

Fuse flown and transistor shorted. Sad

What's the recommended replacement for APT 12082LNR (x)?
Can the quad be measured for fault without high voltage or is it internal arcing at high voltage that kills the transistor?

barclay66 · Posted: Wed Jun 17, 2015 9:26 am Post subject:

Hi,

Repair of an EHT board tends to be quite tricky. Testing the quad too. You might be able to test it for shorts but an isolation problem would go undetected (would need special equipment). I would recommend that You send both parts to Curt for testing/repair...

Regards,
barclay66

winny · Posted: Wed Jun 17, 2015 10:41 am Post subject:

Well, I do have all the high voltage equipment imaginable at work so no problem there. Apply 35 kV and check the quad for flashovers/partial discharge?

From the compability matrix (http://www.curtpalme.com/docs/BarcoServiceBulletin_R762716_New_EHT.pdf), it looks like no luck in converting my new chassis to adopt old EHT and splitter.

barclay66 · Posted: Wed Jun 17, 2015 11:11 am Post subject:

winny · Posted: Wed Jun 17, 2015 12:05 pm Post subject:

Ah, I didn't know that.

Apply pulsed DC on the primary and measure the DC voltage on the secondary?

Is the inductance value for a working one known?

barclay66 · Posted: Wed Jun 17, 2015 1:09 pm Post subject:

Hi,

winny · Posted: Wed Jun 17, 2015 2:16 pm Post subject:

Alright, the schematic was very straight forward. I see no problem exiting the primary of the quad and measure the high voltage on the secondary. Splitter shold be more straight forward.

As for the transistor, can't find any information about APT12082 but old EHT uses IXYS IXTH 12N10, 1 kV 1 ohm. I would suspect APT12082 is 1.2 kV and around 1 ohm and from the schematic, shouldn't be that critical to get exactly the same data otherwise.

Decibel · Joined: 31 May 2007 Posts: 904 Location: Roma - Italia

Any news?

winny · Posted: Sat Jun 20, 2015 3:00 pm Post subject:

Found a 1050 V transistor at work, but 8 ohm so this might not be long lived.

National holiday in Sweden so I'm away from home. Will pick it up on Monday.

**Curt Palme** · Posted: Mon Jun 22, 2015 10:52 pm Post subject:

I've got either complete EHT boards cheap, or the correct transistor, if that one doesn't work.

winny · Posted: Tue Jun 23, 2015 8:01 am Post subject:

Transistor would be nice, sice 8 ohm is 100 times the losses of 0.82 ohm of the original transistor.
ROHM SCT2280KEC should be a good alternative at $8 but if you have the APT12082 laying around, that would be even better.

While we are talking EHT, has anyone tried feeding the 35 kV with a high voltage power supply? I mean straight DC, no 100/120 Hz flicker, no ducking of the brightness in white scenes and probably a bit shorter lifespan of the tubes as well.

gjaky · Joined: 05 Jun 2010 Posts: 2790 Location: Budapest, Hungary

winny · Posted: Tue Jun 23, 2015 4:12 pm Post subject:

Yes, but that comes from the current limit in the flyback stage. If you would remove that, the 400 V cap will be too small.

I was under the impression that the flyback would run out of regulation here and hence the 100 Hz flicker, but apparently not.

Wear a lead apron and enjoy that full 1200 lumen goodness in star wars V or blind your coworkers with that powerpoint!

**Curt Palme** · Posted: Tue Jun 23, 2015 4:19 pm Post subject:

you guys really scare me with some of your posts here... Smile

gjaky · Joined: 05 Jun 2010 Posts: 2790 Location: Budapest, Hungary