6 May
2013
6 May
'13
1:50 p.m.
Reminds me of working on a recent acquisition... a Mac Plus. The display
wasn't working and the case was REALLY dirty to boot, so I removed the
CRT/power supply board and all the other guts to R&R and clean the case in
the kitchen sink. I told my wife who was sitting on the couch, "you're
going to hear a loud snap, so don't freak out." I grounded the tube and...
nothing. On most other monitors I've worked on, I've gotten at least a snap
out of them (especially color ones), but not with this one.
On Mon, May 6, 2013 at 3:22 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Fun times with a TRS-80 Model 4 (such a nice looking machine!).
http://www.classic-computers.org.nz/blog/2013-04-06-replacing-model4-screen…
Why did you replace the CRT? I notice that your final (?) photo has a
caption of the form 'enjoying the green screen', but I thought all M4s
had a green phosphor CRT. Well, M3s that have been upgraded don't I guess.
As regards removing the final anode connector ('anode cap'. 'EHT flower'
:-), etc) most of the time the CRT is automatically discahrged either
via a bleeder resistor or via the beam current of the CRT. The only time
I've had a reasonable residual voltage on the final anode was on a CRT
where the cathode (yes, I mean cathode and not heater) had become
disconnected from the base pin, so no beam current.
The residual charge in any case is unlikely to be dangerous iteslf, but
it may make you jump and hit the CRT or similar.
I use my EHT voltmeter (a Heathkit one cosnisting of an 800M resistor and
50uA meter in series). It passes enough current to discharge the CRT and
of course you can see when it's discharged. But not everybody has such
an instrument (although it's a very useful thing to own if you work a lot
on monitors).
-tony