J
JURB6006
Hi folks, I'm sorta Rod Serling here;
The exact model isn't that important in this case, this is a two board Zenith
RPTV, I think 9-1678 (?) based. Appears to have had a coolant leak from the
blue, it got all over the power/deflection board.
Took the usual cleaning, scraping and soldering to get it running. Fired it up
and it's burning up the fusible(s) on the convergence board. Replaced the STKs
and it still happens. Lacking the print, I figured maybe the power board was
feeding it some overvoltage or something, coolant leaks can do strange things,
so I replaced it. Same deal, but I've now discovered that it'll run with the
blue convegence yoke unplugged.
Naturally I spin the set around and have a look at the tubes. Bone dry. I
thought maybe the coolant was all over that yoke, and it would have to be to
cause this problem, but it's bone dry.
Another thing I noticed was that the blue CRT has been changed and the
replacement is shorter than the other CRTs. Has anyone run into this before ?
Last time I saw this it was unconvergable and deemed an incompatible
replacement by myself and another (highly competent) tech.
There was something about the focus too, but that's not the case here, what's
more we worked on this set last, IIRC it needed a fly or something, a normal
repair. AFAIK we were the last . . .
If you think it's interesting now, stick around. Now I plugged in the red and
green convergence and they converge. No smoke getting out. When I plug in the
blue it makes very very little difference, but for the escape of the smoke. A
convergence yoke with shorted turns would cause this, but no since this is a
current drive circuit, even though the dissipation of the STK would increase
dramatically, the current would be the same. Current is what blows the
fusibles, not the dissipation curve of the STK. Even if you directly short the
yoke, it will simply deliver a current image of the drive, or a mirror image
depending on design, right to the 1 ohm or whatever return resistor they use.
The current will not increase. So what gives ?
This yoke is bone dry and shows no conductance at all between windings on the
higest scale on my Fluke. Also how can there be coolant on the board and
nowhere else ?
Like I said it's like the twilight zone here. I'm getting confusing
indications, but giving up is not an option, this thing has good tubes and we
just worked on it a few months ago. Did maybe the customer pull a switcheroo on
us ? It's not the one with the incompatible tube, you could tell on that one by
the "unnatural" distortion in the raster.
This one looks normal in that respect. Help is greatly appreciated and comments
are welcome.
Thannks in advance.
JURB
The exact model isn't that important in this case, this is a two board Zenith
RPTV, I think 9-1678 (?) based. Appears to have had a coolant leak from the
blue, it got all over the power/deflection board.
Took the usual cleaning, scraping and soldering to get it running. Fired it up
and it's burning up the fusible(s) on the convergence board. Replaced the STKs
and it still happens. Lacking the print, I figured maybe the power board was
feeding it some overvoltage or something, coolant leaks can do strange things,
so I replaced it. Same deal, but I've now discovered that it'll run with the
blue convegence yoke unplugged.
Naturally I spin the set around and have a look at the tubes. Bone dry. I
thought maybe the coolant was all over that yoke, and it would have to be to
cause this problem, but it's bone dry.
Another thing I noticed was that the blue CRT has been changed and the
replacement is shorter than the other CRTs. Has anyone run into this before ?
Last time I saw this it was unconvergable and deemed an incompatible
replacement by myself and another (highly competent) tech.
There was something about the focus too, but that's not the case here, what's
more we worked on this set last, IIRC it needed a fly or something, a normal
repair. AFAIK we were the last . . .
If you think it's interesting now, stick around. Now I plugged in the red and
green convergence and they converge. No smoke getting out. When I plug in the
blue it makes very very little difference, but for the escape of the smoke. A
convergence yoke with shorted turns would cause this, but no since this is a
current drive circuit, even though the dissipation of the STK would increase
dramatically, the current would be the same. Current is what blows the
fusibles, not the dissipation curve of the STK. Even if you directly short the
yoke, it will simply deliver a current image of the drive, or a mirror image
depending on design, right to the 1 ohm or whatever return resistor they use.
The current will not increase. So what gives ?
This yoke is bone dry and shows no conductance at all between windings on the
higest scale on my Fluke. Also how can there be coolant on the board and
nowhere else ?
Like I said it's like the twilight zone here. I'm getting confusing
indications, but giving up is not an option, this thing has good tubes and we
just worked on it a few months ago. Did maybe the customer pull a switcheroo on
us ? It's not the one with the incompatible tube, you could tell on that one by
the "unnatural" distortion in the raster.
This one looks normal in that respect. Help is greatly appreciated and comments
are welcome.
Thannks in advance.
JURB
