On 06/15/2014 10:55 PM, Tony Duell wrote:
During preparation of the machine for VCFE i had a failure in the CRT's high voltage
part.
Yep, flyback burnt..
The high voltage winding was potted as a separate unit, enabled my to
rewind the flyback's primary (was burnt).
Are there only 2 windigns? What
about any taps on them? A single shorted
turn anywhere will cause problems.
No taps, but extra windings for CRT filament.
Hissing often means corona/brush discharge, nnot
sparking. Did you
reoslder anything on the EHT side (connections to the diode, capacitor,
etc). If so, an 'icicle' fo solder cna be annough to cause this, you want
well-roudned sodler blobs
It could also be internal breakdown in the winding (in fact it sounds
like it is).
Is there a spearate capacitor? Often it's just the coatingso n the CRT.
It has
a separate 1.5nF Hv capacior.
Yes, the rectifier diodes do fail, often. But if it was shorted you would
get no display at all.
What fialed after the few seconds? The output transistors?
The HV diode
connection.... Primary side is still OK.
Come to think of it, that might have caused the hissing.
When I get the replacement diodes I will try again.
If it fails again, I will rewind the primary again, and increase the windings by 10%, in
order to reduce HV output.
Is the service manual/scheamtic on-=line anywher
Several Ball monitors on Bitsavers, but not this model, not even close. I will trace the
schematic if required.
Does the flyback
transofrmer/output stage do anyhting other htan supply the HET (is i nteh
orizontal defleciton stage too)?
It also supplies the CRT filament, and some secondary gate voltages.
And yes, also the horizontal deflection.
I did have some instabilities in the horizontal deflection for some time, come to think of
it.
> It is a 17 inch white monochrome Ball HD17-type
monitor.
> What are my options : repair ag ain,
looking for a generic flyback ( is
> there such a thing ?) , or dumping it into lake Zurich, which is my
> current mood....
> Don't do the last, I am not
particularly 'green' but don't approove of
> polution. Quaiate apart from the fact that the machine is worth
As you probably guessed, that was not a serious suggestion.
Here in .CH you can just bring your waste electronics in for free.
Last time i did that i was rewarded with a P2000C, with manuals and original floppies.
In 2014 that is...
Took it home, booted first time...