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maxhifi 11-16-2017 05:56 PM

Wirewound Resistor Lesson
I posted another thread about counterfeit STK modules. Anyway the bad ones I got blew two 1.8 ohm 2W resistors on the convergence board of my Runco/NEC projector. I got the new modules, and I changed the resistors to 5W wirewound ceramic resistors, and suddenly all week, the projector would randomly become unstable, text would twitch and vibrate periodically, and then snap back to normal. Subtle but really annoying if you knew to look for it.

I thought OK it never did this before, what's different? Well, 2W metal film resistors fixed it.. it's totally stable now. Learn something every day, I guess!

Must have been the inductnce of the wirewound resistors messing things up.

MadMan 11-16-2017 11:28 PM


Originally Posted by maxhifi (Post 3192136)
Must have been the inductnce of the wirewound resistors messing things up.

Intermittently, though? That's odd, if it was the inductance, wouldn't it be 100% of the time? Maybe they were defective or something. Internal short?

zeno 11-17-2017 08:59 AM

I would guess so. You cant use WW resistors to sub in
many places especially high freqs. Also those resistors are
being used for fuses for the STK's. Going to 5W risks
damage to usually the FBT if ( when) the STK shorts again.
The only time to use them is in a quick test or a smoke test.

73 Zeno:smoke:

Electronic M 11-17-2017 06:40 PM

Some wire wounds have dis-similar metals joined that can form PN junctions and potentially have contact vary with thermal expansion...That may have something to do with the issue being intermittent.

maxhifi 11-17-2017 07:12 PM

Makes sense they are used as fuses. I think Zeno is right with if (when), I got the projector in 2005, changed the modules in 2012,2013, and 2017. Tubes still have lots of life, I packed away three spare modules.

I started using the projector a lot more after 2010, when I got netflix.

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