FW900 - Spark gap SG901 going off - Repair assistance?

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DejahThoris
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Joined: Sat Oct 19, 2013 10:26 pm
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FW900 - Spark gap SG901 going off - Repair assistance?

Post by DejahThoris »

I know this can be a shorted tube, bad flyback, or any number of things. Is there a good way to narrow it down?
DejahThoris
Posts: 719
Joined: Sat Oct 19, 2013 10:26 pm
Location: Riverside, CA

Re: FW900 - Spark gap SG901 going off - Repair assistance?

Post by DejahThoris »

Well, swapped in a known good PSU board, FBT board, Input board, Neck card, and whatever the other PCB on the rear of the monitor is.

Same problem persists.

https://photos.google.com/photo/AF1QipP ... cj9KRUDYFs

I'm assuming shorted tube? Unless the PCB under the neck is somehow responsible, but I'm pretty sure that's not terribly important in the scheme of getting HV to the tube.
SuperSpongo
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Re: FW900 - Spark gap SG901 going off - Repair assistance?

Post by SuperSpongo »

You could check the tube for shorts with a CRT Tester/Rejuvenator like the Müter BMR line. Sorry, I don't know if there are equivalents in the US. I wouldn't trust an FW900 Trinitron tube with a crusty B&K 467.. I've read good things about Sencore?
DejahThoris
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Joined: Sat Oct 19, 2013 10:26 pm
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Re: FW900 - Spark gap SG901 going off - Repair assistance?

Post by DejahThoris »

SuperSpongo wrote:You could check the tube for shorts with a CRT Tester/Rejuvenator like the Müter BMR line. Sorry, I don't know if there are equivalents in the US. I wouldn't trust an FW900 Trinitron tube with a crusty B&K 467.. I've read good things about Sencore?
Unfortunately I've no idea what the proper adapter is, or the necessary information to use a universal adapter.

Funny enough I have a B&K 466.

I don't think this is likely worth buying a different rejuvenator for. Lots and lots of leaky tube threads throughout the years for this model, and I wouldn't be a bit surprised if that's the case here too.

Just turned it on in the dark and get the arcing in the neck you'd expect out of a cracked tube. Hadn't noticed before because I was so intent on the spark gap being related to the problem.


Guess I now have spare parts for the working FW900 at least? What a bummer.
SuperSpongo
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Re: FW900 - Spark gap SG901 going off - Repair assistance?

Post by SuperSpongo »

Tube is M57LRX15X. The Müter uses adapter 898.
The service manual of the FW900 shows the pins on the silk screen (page 5-23). You could repurpose one of your adapters to build a universal one. I used to have a 467 and looked up the pinout. Here's a link:

https://www.radios-tv.co.uk/community/g ... 3-adapter/

That being said, I don't know if you can use the B&K on a high end Trinitron tube like that. Then again, it's already broken, so there's not much to lose either way? :mrgreen:

I have a friend who unsuccessfully tried to fix a short in an FW900 tube. If you want, I'll shoot him a message, maybe he can chime in as well.
DejahThoris
Posts: 719
Joined: Sat Oct 19, 2013 10:26 pm
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Re: FW900 - Spark gap SG901 going off - Repair assistance?

Post by DejahThoris »

SuperSpongo wrote:Tube is M57LRX15X. The Müter uses adapter 898.
The service manual of the FW900 shows the pins on the silk screen (page 5-23). You could repurpose one of your adapters to build a universal one. I used to have a 467 and looked up the pinout. Here's a link:

https://www.radios-tv.co.uk/community/g ... 3-adapter/

That being said, I don't know if you can use the B&K on a high end Trinitron tube like that. Then again, it's already broken, so there's not much to lose either way? :mrgreen:

I have a friend who unsuccessfully tried to fix a short in an FW900 tube. If you want, I'll shoot him a message, maybe he can chime in as well.
Thanks!

I'd certainly appreciate it!

I'm pretty sure we've lost vacuum at this point and it's got air in it, but it can't hurt to try.
DejahThoris
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Location: Riverside, CA

Re: FW900 - Spark gap SG901 going off - Repair assistance?

Post by DejahThoris »

Final update:

Decided I'd pull the yoke to see if there were any cracks I could see in the tube, and half the neck came right off with it. I'd say she's toast, lol.

Crack's right where the band to secure the yoke is too, I bet the previous owner over-tightened it...
SuperSpongo
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Re: FW900 - Spark gap SG901 going off - Repair assistance?

Post by SuperSpongo »

Oof, RIP. :|
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