barry@vaxwaller.UUCP (Barry Nesmith) (05/30/84)
I've been in charge of maintenance on our Televideo terminals for about a year now. We also have one or two a month breakdown. It seems that capacitor C306 on the video board has a high mortality rate. There was a bad lot of this capacitor and it seems like they will probably all eventually fail. They can fail in a number of different ways. I have had them cause a loss of video (occasional loss as well as permanent loss), loss of horizontal and vertical deflection so that only a horizontal or vertical line appears on the screen, occasional glitches in the screen (sometimes audible) which cause the terminal to crash requiring power to be turned off and back on again, the internal fuses to blow sporadically (usually a sign that the capacitor is about to totally go), and several times the cap has actually blown up. (not necessarily dangerous but it does create a foul odor) I have replaced about 25-30 of these caps so far. There's no need to replace them unless they actually are defective. I assume this is a common problem with terminals that were shipped about two years ago. The capacitor in question will be gray or light violet. It is on the video board. (We mostly have 912's and 925's but I believe that the video board is the same on the 950) The capacitor is about an inch high. The replacement cap is green and about 2 inches high. The original (bad) cap is 20 uF 50V. The replacement is 16 uF 25V. Note that both these caps are NON-POLARIZED. If you attempt to replace the cap be very careful since the CRT can hold a painful charge for long after it has been turned off. Televideo has been very cooperative with help for this problem. If you supply them with the serial number of your defective terminals they will probably send you the replacement caps at no charge. They have also been very quick about sending them. You can call them at 800-438-8725 ext 439 outside California or 800-745-7760 ext 439 in California. I don't know for sure if this is the cause of your power supply problems but from my experience I'll bet it is. As to blowing out flyback transformers I don't know, except for the fact that C306 is connected to the primary of the flyback transformer. This might be yet another failure mode that I have not yet encountered. Good luck. Barry Nesmith Varian Associates Walnut Creek, Calif
bob@islenet.UUCP (Robert P. Cunningham) (06/01/84)
I'm temporarily managing a site with about 40 or so Televideo TVI 950
terminals (among others). Much to my surprise, the 950's seem to have a
terrible failure rate. About once a week an arbitrary TVI 950 either
has a power supply failure or burns out a flyback transformer.
We send back quite a few still under warranty when they burn out
within a few days or weeks of arrival. Just before I took over, the
site put in yet another mixed bulk order of 950's & 924's that we'll
be receiving over the next month or so. And I'm expecting to be stuck
with more trouble.
I'd appreciate any suggestions on possible causes and cures for this
strangely high terminal mortality rate.
--
Bob Cunningham ..{dual,ihnp4,noscvax,uhpgvax,vortex}!islenet!bob
Honolulu, Hawaii