Looking for a flyback transformer for an Eizo TX-C7 MA-791 17" CRT

[retrotechrestoration]

I just saved this magnificent RGB input Eizo Flexscan TX-C7 MA-791 from the local e-waste...good news, the tube works and the board looks great...the bad news, it sounds like the flyback is shorted. (Turns on...perfect picture...systemic high voltage crackling heard while the picture flickers...then it blows the 5A fuse in my isolated A/C power supply.)

Anyone have any leads on possibly finding a replacement? (photo shows the flyback model numbers)

[retrotechrestoration]

Photo...

[retrotechrestoration]

And according to this site, an equivalent FBT might be the HR46290.

https://www.hrdiemen.com/search/index?orig=&page=1574

[momaka]

If the picture on the screen comes up and you don't hear or see high-voltage arcing noises, then the flyback is not faulty.

Picture "flickering" suggests the degauss coil relay might be stuck in the On position... or if the monitor doesn't have a degauss coil relay, then the PTC in series with the degauss coil is somehow allowing excessive current.

Either way, here's a quick test to perform: disconnect the degauss coil from the main board and see if the picture still "flickers". If it doesn't and your fuse doesn't blow up anymore, then that's likely the issue.

Also, I wouldn't worry about connecting the monitor directly to the wall without an isolation transformer / PSU. CRT monitor PSUs are usually pretty well protected against short-circuit and other faults. So nothing should burn up (degauss coil PTC excepted, of course, if there's a relay for it and it's stuck ON.)

[retrotechrestoration]

As I mentioned, it is making high voltage crackling, arcing sounds coming from all parts of the monitor, but I'll definitely check the degauss relay.

Thanks

[eccerr0r]

reminds me of a 14" VGA monitor I fixed years ago... there was a hole in the FBT that leaked HV out the side to the closest chassis ground, wicked spark... I stuffed it with plastic and it insulated enough for the crt to work... hah.

hmm that fbt looks similar to one i pulled from a 17" crt I drop cracked... wonder if i still have it...

[retrotechrestoration]

reminds me of a 14" VGA monitor I fixed years ago... there was a hole in the FBT that leaked HV out the side to the closest chassis ground, wicked spark... I stuffed it with plastic and it insulated enough for the crt to work... hah.

hmm that fbt looks similar to one i pulled from a 17" crt I drop cracked... wonder if i still have it...

This FBT looked pretty well intact, but I'll go over it more closely when I get home.

If you happen to have a matching FBT, you'd have my undying gratitude and some fresh cash in your PayPal account!

[eccerr0r]

Nope, sorry to get your hopes up, it's different though reminiscent...

[stj]

have you run it in the dark with the back off?

[momaka]

I'll take a look inside my parts boxes as well, since I do recall having saved the boards from a CTX monitor that has a similar flyback.

However, do as sjt noted first - take a look inside the CRT to see if there is any arcing.

Also, I'm pretty sure the flyback, even if it is faulty (which I doubt) can make the fuses on your isolated PSU burn up.
The way pretty much all "modern" CRT TVs and monitors work is there is a main switching power supply inside that produces B+ (160-200V typically) and this B+ is then driven by the HOT (horizontal output transistor) to drive the flyback transformer. So if the flyback traffo was bad, it would pull B+ down and this would shut down the main SMPS. So it's just not possible for the fuse to blow simply from this circuit design. So don't replace the flyback blindly. Troubleshooting CRT monitors by method of shotgunning parts is usually the longer and harder way to getting them fixed.

Again, take a look at the degauss coil and particularly, try disconnecting it. This is the only thing that can draw such a high current to burn out your fuse. If the main SMPS was dead, the monitor wouldn't even try to start or make any noises - it would instantly be blowing fuses.

[retrotechrestoration]

I'll take a look inside my parts boxes as well, since I do recall having saved the boards from a CTX monitor that has a similar flyback.

However, do as sjt noted first - take a look inside the CRT to see if there is any arcing.

Also, I'm pretty sure the flyback, even if it is faulty (which I doubt) can make the fuses on your isolated PSU burn up.
The way pretty much all "modern" CRT TVs and monitors work is there is a main switching power supply inside that produces B+ (160-200V typically) and this B+ is then driven by the HOT (horizontal output transistor) to drive the flyback transformer. So if the flyback traffo was bad, it would pull B+ down and this would shut down the main SMPS. So it's just not possible for the fuse to blow simply from this circuit design. So don't replace the flyback blindly. Troubleshooting CRT monitors by method of shotgunning parts is usually the longer and harder way to getting them fixed.

Again, take a look at the degauss coil and particularly, try disconnecting it. This is the only thing that can draw such a high current to burn out your fuse. If the main SMPS was dead, the monitor wouldn't even try to start or make any noises - it would instantly be blowing fuses.

Good point... in addition, when I re-attached the FBT and tested it, there were no more arcing sounds... just the initial degauss "fwumpf" sound before the onboard power supply fuse and my external power supply fuses both blew.

I'll remove the deguass coil, inspect it and test again, but it seems like you may be right on the money.

Props!

[retrotechrestoration]

Good point... in addition, when I re-attached the FBT and tested it, there were no more arcing sounds... just the initial degauss "fwumpf" sound before the onboard power supply fuse and my external power supply fuses both blew.

I'll remove the deguass coil, inspect it and test again, but it seems like you may be right on the money.

Props!

*sigh* No change with the degauss coil(s) unplugged. This monitor has two coils-an inner and and outer. I'm currently tracing my way through the power supply circuit...will post if I find anything.

[retrotechrestoration]

The hum wasn't coming from the degauss coil...it was coming from the main transformer. There's no fault and cleanly regulated power going all the way to its inputs when the transformer is out of circuit.

[momaka]

OK, hold up a bit... I don't see a main input cap on the primary side, so this doesn't look like a conventional switch-mode PSU.
What happens when you plug in the monitor directly in the wall without the isolation PSU? Do this with the monitor's flyback installed. If there's a fault, let the fuse on the monitor power board handle it. I just want to make sure we are not chasing a "ghost" problem with the isolation PSU not being able to handle some kind of a high startup current that the monitor may normally have. If the fuse on the monitor board blows, then we know something needs looking after.
The PSU primary looks like some kind of a LLC / oscillator type found in electronic halogen lighting transformers, so not sure how that should act up with a fault on its secondary side, if there is one at all. I do see two optocouplers, so there is definitely some kind of regulation/feedback/protection going on. Might have to find a service manual for this one...

[retrotechrestoration]

OK, hold up a bit... I don't see a main input cap on the primary side, so this doesn't look like a conventional switch-mode PSU.
What happens when you plug in the monitor directly in the wall without the isolation PSU? Do this with the monitor's flyback installed. If there's a fault, let the fuse on the monitor power board handle it. I just want to make sure we are not chasing a "ghost" problem with the isolation PSU not being able to handle some kind of a high startup current that the monitor may normally have. If the fuse on the monitor board blows, then we know something needs looking after.
The PSU primary looks like some kind of a LLC / oscillator type found in electronic halogen lighting transformers, so not sure how that should act up with a fault on its secondary side, if there is one at all. I do see two optocouplers, so there is definitely some kind of regulation/feedback/protection going on. Might have to find a service manual for this one...

Thanks for the suggestion. I did try powering it up directly off the wall circuit, and the onboard fuse near the mains input did blow rather spectacularly. I saw the optocouplers. I've tested the relay that crosses the two board sections out of circuit and most of the other psu components. They've all tested good.

I'm still looking for a service manual.