Magnavox safety cap problem

[Jon A.]

Just wondering what years and chassis are known to cut a neck and how to identify the faulty-design caps and their replacements.

Thanks.

[zeno]

Originally Posted by Jon A.

Just wondering what years and chassis are known to cut a neck and how to identify the faulty-design caps and their replacements.

Thanks.

IIRC they were 19" T-991 chassii. Same as Zenith change any white
4 lead caps. Values are different than Zenith !
If you get any Maggy upright chassis before anything else resolder
everything on the HV side of chassis including grounds. Also
do the modules themself. Smaller sets had a board in behind
that must be done, they burned up L&R from cold joints.
Some had plug in FBT's be sure the pins arent toasty. Same
with the module pins.

73 Zeno

[radiotvnut]

The 19" T991 and T809 chassis, along withe the 25" T995 and T815 chassis, had the 4-lead safety capacitors. They were a high failure part and they would usually short, causing the circuit breaker to trip. Sometimes, they would open and cause the HV to blow the neck off the CRT.

To my knowledge, the 4-lead capacitors are no longer made. A few years ago, I had a T809 with a shorted cap come my way and I replaced it with a combination of Sprague HV orange drop capacitors wired in parallel to give me the right value. I guess it held up because the TV didn't come back.

Like what has already been said, bad solder connections on the flyback and modules were a very common problem.

[Jon A.]

I reckon NOS caps are still out there as well. I have a couple of Zenith 4-lead cap kits just in case.

[radiotvnut]

They show up from time to time; but, the ones I remember being in Maggies were not that reliable and I'd rather go with something better. The ones I remember were grey in color.

[Jon A.]

Where would I get the Sprague caps? I think I read something here about certain terminals on the chassis needing to be bridged when installing reliable subs.

So the T991 is a vertical chassis? What about the T995?

[radiotvnut]

All the ones I mentioned are a vertical chassis. The T991 was in use from around '75 until '78-'79, as was the T995. The T815 and T809 were around from about '79 until around '82, when they were replaced by the two board 19/25C1 chassis.

[Jon A.]

All vertical, isn't that something. My existing sets have some vertical boards but that's it. I assumed the 815 and 809 were older than the 991 and 995, so much for that. Not much changed except for the switchover to inline CRTs I assume. Got to keep my eyes open for bulk discounts on service manuals.

[rca2000]

Actually, I believe is is the other way around. The 809 and 815 are a bit NEWER than the 991. ALL are pretty similar, the biggest difference is the 815 is a cold chassis, I believe it had a VRT power transformer also. The 809 and 991 are hot. Most modules between the 809 and 815 are the same, IIRC< other than the power supply and maybe the pincushion module or such.

[Jon A.]

I guess I could have worded that better, I had just assumed that the 809 and 815 were older before radiotvnut's most recent post. Anyway, I'm still wondering about the finer details of the Sprague caps: where to get them, how to install them (assuming they're regular 2-lead caps), if they're actual safety caps, and if not, that they're pretty much guaranteed to short on failure rather than open.

[radiotvnut]

I got the capacitors from antique electronic supply and I had to order two capacitors to wire in parallel to give me the correct value. The new capacitor only had single leads; so, I jumped together the end leads where the original cap connected. The whole purpose of the 4-lead cap was that the internal interlock of the cap was supposed to open if the cap blew apart. Unfortunately, the interlock does not always open when the cap blows apart and that's why the HV runs up. When the interlock opens, it disables the horizontal output stage.

[Jon A.]

Oh okay, I think I've got it now. So the two-lead caps like those in my 25DC56 don't even have a safety interlock, they just open or short, and the way you wired yours is a failsafe that will open both connections if the cap opens.

[zeno]

Along with OEM's others sold the caps under generic names.
There were quite a few of them including some 2 lead
jobs for GE etc. They are out there somewhere........

73 Zeno

[Jon A.]

I was thinking, wouldn't the HV still spike if one of the parallel-wired caps were to open?