exxos's Atari, Amiga & retro forum

JezC wrote: 16 Feb 2022 22:20

rubber_jonnie wrote: 16 Feb 2022 21:50 I'd love a Malamute, but I also like my stuff the way it is and the cat is bad enough!!

Ah yes...our sole remaining cat has a penchant for biting through thin cables - apparently it's a Savannah thing! - so I fully understand your concerns...but our Mal, Jet, is far less destructive than Bagheera.
It's more like having a small donkey wandering around in the house wooing at everybody.

Not to mention how her favourite person is always the one with food...and if it's a toasted teacake with butter you're likely to get her undivided attention!

:threadjacked:

Anyway, enough of these diversions...better get back to planning my next retro repair!

:)

And what repair will it be?

rubber_jonnie wrote: 16 Feb 2022 22:25 :)

And what repair will it be?

Fixing the horizontal offset on that SM124 is top of the list for now...hopefully an easy fix for once!
Just giving the HT circuitry time to discharge, so will probably post the results tomorrow ;)

JezC wrote: 16 Feb 2022 22:31

rubber_jonnie wrote: 16 Feb 2022 22:25 :)

And what repair will it be?

Fixing the horizontal offset on that SM124 is top of the list for now...hopefully an easy fix for once!
Just giving the HT circuitry time to discharge, so will probably post the results tomorrow ;)

Splendid :)

I don't have good memories of working on CRT's, when I was ~14 I had dropped my Commodore 1901 monitor and managed to cracked the main circuit board, I bodged it all together with patch wires and solder and amazingly it worked (I knew next to nothing about electronics then - and haven't come much further since :lol: ). Being a bit thick I was running the monitor with the cover off and decided to flip it onto it's front to inspect something underneath - I found myself in a heap on the floor feeling a bit 'shocked' after lightly touching the sides of the mainboard. Both parents came belting into the room shortly after having heard me shriek involuntarily at the top of my lungs.

I have a very healthy respect for electricity these days :lol: :oops:

So legend tells us, when working on a CRT, the trick is to put one arm behind your back so the current doesn't make a circuit through your arms and heart!

Can't remember where I heard that, but it kind of stuck with me because I need all the help I can get when I eventually have to tackle the Mitsu 37" CRT leviathan!

I doubt I will get anything as meagre as a shock off of that... I'm either going to be OK, or dead, ready to be scooped into an urn, if I get it wrong! :(

mrbombermillzy wrote: 17 Feb 2022 11:59 So legend tells us, when working on a CRT, the trick is to put one arm behind your back so the current doesnt make a circuit through your arms and heart!

Well in this case, you ought to work only with the right arm, and lift the left leg straigth toward the left, so that any curent running through your body can do so only on your right side... (of course, if you are among the rare number of people that have the heart on the right side, work with the left arm and lift your right leg)

@sporniket Thanks for the extra details!

Don't worry, if I ever do it, I will be wearing thick rubber gloves, 2" rubber soled platforms and will be distributing several earthed copper rods around the room.

NOTHING will be taking a route through my internals! :lol:

mrbombermillzy wrote: 17 Feb 2022 11:59 So legend tells us, when working on a CRT, the trick is to put one arm behind your back so the current doesnt make a circuit through your arms and heart!

Can't remember where I heard that, but it kind of stuck with me because I need all the help I can get when I eventually have to tackle the Mitsu 37" CRT leviathan!

I doubt I will get anything as meagre as a shock off of that... I'm either going to be OK, or dead, ready to be scooped into an urn, if I get it wrong! :(

Sorry @Icky you've been :threadjacked: again!

I have read/watched a lot about CRTs of late with doing a lot of work on my Mac Classic. It may only have a 9" screen, but the 13Kv anode voltage is certainly enough to make you feel 'unwell', in the sense that unwell=dead!!

I tried to work with one hand behind my back, but often, to my annoyance, found I was using both hands and had to correct myself. Since a lot of what I did was adjustment, then I used plastic tools anyway as recommended, and was able to manage one handed. The Mac also has discharge resistors, so that made it safer, but I did make a discharge tool for the anode cap and discharged as recommended for the Classic, though I never once had a 'crack' from a discharge.

The mains filter electrolytic was also scarily zappy unless you allowed some time for it to discharge!!

The key takeaways for me was to understand what I was working on. Schematics are going to be essential for you, and I also suspect you may want some specialised tools. I know you can buy CRT voltage checkers that also allow you to discharge, and knowing what safety features are built in is a big help.

The main thing is, just be bloody careful!!

Gone are the days when my uncle was a TV repairman when he used to lick his finger and touch the tops of some of the vacuum tubes to strike an arc between it and him!!

rubber_jonnie wrote: 17 Feb 2022 13:46 Sorry @Icky you've been :threadjacked: again!

Yeah, sorry! :)

rubber_jonnie wrote: 17 Feb 2022 13:46 The key takeaways for me was to understand what I was working on. Schematics are going to be essential for you, and I also suspect you may want some specialised tools. I know you can buy CRT voltage checkers that also allow you to discharge, and knowing what safety features are built in is a big help.

Unfortunately, this thing is like the proverbial hens teeth. In all my years since owning, searching for any info, I found one photograph and a quick spec. writeup for a small news column.


So it literally will be a case of try and see.

Yikes, sounds like you're gonna have to be super careful.

I guess if the hairs on the back of your hands and arms are sticking up, you need to step away from the monitor :lol: