CRT long warmup time?

[john]

Any ideas as to what would cause a CRT to take 10mins to warmup before it displays anything? Maybe old capacitors? This thing is a 55 year old calculator.

-John

[Peter W.]

On Thursday, June 15, 2023 at 1:02:30 PM UTC-4, john wrote:
> Any ideas as to what would cause a CRT to take 10mins to warmup before it displays anything? Maybe old capacitors? This thing is a 55 year old calculator.
>
> -John

Once upon a time we had a solid-state CRT television that would sit for a few minutes before showing a picture. We would hear a *POP* and the picture would come up. After which it would behave normally. I expect it was some transistor or other in the video section that started to conduct after time. Either it was weak, or as you suggest, the supply to it was weak - from caps or some such.

We lived with it until we moved - and it stayed behind.

Peter Wieck
Melrose Park, PA

[Phil Hobbs]

On 2023-06-15 13:02, john wrote:
> Any ideas as to what would cause a CRT to take 10mins to warmup before it displays anything? Maybe old capacitors? This thing is a 55 year old calculator.
>
> -John
>

1968 is a bit young for wax capacitors, which are always bad. A dying
electrolytic in some grid circuit would get my vote.

Cheers

Phil Hobbs

[john]

As it turns out the caps are excellent and the voltages rock steady. Almost unbelievable for a 50 year old device (an HP-9100B).
The 24V supply was for some reason at 31V. I tweaked it down with an adjustment resistor on the cards, and the CRT came up in 12 seconds. Manual says within 20 secs - so it seems fine. Thanks! -John

[Jeff Layman]

On 19/06/2023 00:23, john wrote:
> As it turns out the caps are excellent and the voltages rock steady. Almost unbelievable for a 50 year old device (an HP-9100B).
> The 24V supply was for some reason at 31V. I tweaked it down with an adjustment resistor on the cards, and the CRT came up in 12 seconds. Manual says within 20 secs - so it seems fine. Thanks! -John

I spent some time with its successor - the 9810A
(https://www.oldcalculatormuseum.com/hp9810a.html) in early 1972. As
that article notes, it was a choice between the HP and a Wang. The HP
was a great machine, and quite easy to program although I had to get
used to RPN.

It was being used in a lab, and my boss used to program it as well. I
well remember one day when he'd spent hours inputting a big program
(IIRC around 1600 steps) when his office phone rang. He left the machine
to answer it, and a few seconds later the student who was with us on a
job experience program came in to use the machine. He didn't check if it
was in use, and just turned it off and on again to do what he wanted. I
never knew my boss had such a vocabulary of swear words, and the student
hid somewhere until the boss had calmed down! Mind you, if he'd only
paid attention and followed the instructions to now and again record on
the magnetic cards what he'd done, he'd not have lost hours of work.

--

Jeff

[ohg...@gmail.com]

On Thursday, June 15, 2023 at 1:02:30 PM UTC-4, john wrote:

> Any ideas as to what would cause a CRT to take 10mins to warmup before it displays anything? Maybe old capacitors? This thing is a 55 year old calculator.
>
> -John

Does the display suddenly appear nice and bright after 10 minutes of darkness or does it slowly fade to life? Either can be circuit component issues but a slowly appearing image sounds like a very tired CRT. If it's the latter and the machine hasn't been used in many years, then just running it several hours a day will generally perk up a tired CRT.

If the image appears suddenly and looks good, then it's most likely a circuit issue. A service manual would be handy in checking to see if the heater voltage and HV appear immediately (the two most likely issues). If all the voltages are good, then you need to scope the grid of the CRT backwards and see where you are losing you video.