🚀 go-pugleaf

Hello *

I had responded via private e-mail to the gentleman with the Heathkit
terminal and fading display.  Since there's been some followup to the
group, I thought a summary would be useful.

This information applies to the Heath H-19a terminal.

I had the 'fade out/fade in' problem some time ago while doing
classwork.  The display would fade out over about a 10 second period,
fiddling with the brightness control wouldn't help, and it would fade
back in sometime later.  Was driving me nuts.  Especially when trying
to debug the class project for Intro to Databases.

Filiment power for the CRT is developed from a six-turn winding around
the flyback transformer.  This winding is routed through a Molex
connector to the main analog board in the bottom of the set, via some
traces, through another Molex connector to the small board under the
CRT, and finally to the CRT pins via a small 7 (9?) pin push-on
connector.

In my case, one of the molex connector pins sticking up out of the
main analog board had developed a crack all the way around the pin.
Depending on the temperature of the pin, it would sometimes make
connection, sometimes not.  It worked okay when cold.. but would start
getting flaky maybe a half-hour later.  Then the display would start
to oscillate between full brightness and nothing-at-all.

It was fairly easy to remove the analog board... remove the logic
board, undo the screws, and carefully manipulate the analog board out
from under the CRT.  Resolder the offending pin, reassemble, and
apply power.

The Molex connector used by Heath in that terminal has a pin/socket
scheme with a point-contact connection.  The point-contact, under the
right conditions, will develop a great deal of heat due to resistance
at the point.  This heat can get high enough to melt the solder off
the pin.  The connector bodies might discolor a little (didn't in the
Heath but did in another piece of equipment here)

Next time it happens, look inside the unit and see if the filiment is
glowing.  If it isn't then you might have the same problem I did.

Hope this has been of some help.

Regards,
Mark
mbeck@ai.mit.edu