Re: Tempest monitor severe jaggies R901 hot

>
> > Hi All,
> >
> > Well, I'm back again with another tempest problem (you see,
> > I bought the game to work and it is on _all_ the time).
> > This is the second failure in about two months. Last time
> > I burnt Q901, and R903. Replaced both of them and put in a
> > Bob Roberts cap/upgrade/reliability kit (though I only
> > installed the HV part). Monitor does have an LV2000
> > installed.
> >
> > Anyway, I came in a couple of week ago and the HV was gone
> > again. I finally pulled the monitor yesterday and found
> > that R901 was open. Replaced it, got HV back but now every
> > vector is severely jagged and R901 is running hot (it
> > started to smell shortly after powering up, another 30
> > seconds and it would have burnt open).
> >
> > A while back I posted that my HV cage ticks. I was hoping
> > the work I did before would fix that but it still ticks and
> > I was wondering if this could be related.
>
> All symptoms point to runaway HV!!! The "ticks" are arcs either THROUGH
the
> insulation of the secondary anode wire to the HV cage/cover or from the HV
> trasnfomers pins to the monitor chassis. THIS IS VERY BAD and can be very
> dangerous!!! At a minimum it will kill your HV transformer in fairly
short
> order. Check the 7-9ish pin connector for B+ which should be around 180V
> (check the schematic). My guess is that your is 300V+. Why? Well that's
> the kicker; it could be many things. Start with the 3 cap-kit transistors
> as these FREQUENTY short out causing this condition. Basicly look at any
> current paths in front of the resistor which is burning up. Look for
> shorted transistors and/or shorted diodes. Trust me, you will find them.

I have seen two different HV cages fail with a similar problem.

In the first case the monitor was dead, F100 had a blown 10 amp fuse in it!
On the HV cage R903 was toast along with Q901 and Q902.
The deflection board had low voltage regulator problems.
I installed an LV2000, a 5 amp fuse and switched out the HV unit and it ran
again.
It ran good for a long time even under 24/7 conditions.
Eventually it crashed again.
This time I found F101 blown. I replaced it with a 6 amp (all I had on me at
the time) and magic smoke came out of the HV cage.
Again toasting R903, Q901 and Q902.
This time however the deflection board had the LV2000. It survived but I
found Q102 bad. The +25v 2n3716.

I seems to me that loss of low voltage coupled with over-fuseing
consistently caused these problems.
In the second case the regulator was beefed up so the new weak link became
Q102.
I thought it was suggested to up F100 and F101 to 6.25A when an LV was in
use so I figured a 6A would be O.K.
Perhaps when I install a LV2000 I will replace Q102 and Q103 with fresh
transistors.

I almost forgot the failed Q102 was an ECG.
Why would this matter?
I have found countless pre mature failures with NTE or ECG products.
I could go on to say I hate NTE and ECG.
I know it is a convent source, but they always seen to fail again.
Especially in power transistor situations like this monitor or Rowe juke box
amps.
I think their crosses are too generalized.
Sometimes for quick troubleshooting I just scan for NTE/ECG and start there.
It is worth the time to hunt down better parts.

Max

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Received on Sat Oct 21 23:29:58 2000