Microvitec Cub goes 'whistle warble click click'

classic non-acorn hardware, software & languages
Post Reply
User avatar
ChrisJC
Posts: 46
Joined: Sat Jan 16, 2021 2:01 pm
Contact:

Microvitec Cub goes 'whistle warble click click'

Post by ChrisJC »

Morning All,
I've got another Cub that I have partially repaired, and now it superficially works OK.
(the problem was a short circuit in the large orange capacitor on the supply to the TDA1170, causing the 10R resistor to blow, and the frame to collapse to a single line).

But although there is now a good picture, there are two more subtle issues:
1. High pitched whistle / warble (I could live with this if it is OK in the long term)
2. High voltage discharge style 'click / crack' noise. For each noise, there is a visible artefact, like a horizontal displacement of the scan line that it is on, or the scan line lights up a little. It sounds like some insulation is breaking down and a spark being generated. I have removed the cover and observed in a dark room, but can't see anything.

I am thinking that the Tripler is probably breaking down internally causing the clicking noise, and that the Line Output Transformer is mechanically loose allowing the whistling noise.

Does that sound like a reasonable diagnosis?

If it is, can the Tripler and LOPT still be purchased?

Thanks,

Chris.
chrissawer
Posts: 71
Joined: Mon Aug 10, 2020 9:04 am
Location: West Yorkshire, UK
Contact:

Re: Microvitec Cub goes 'whistle warble click click'

Post by chrissawer »

There is a nice recent writeup of Cub refurbishment here: https://retrorepairsandrefurbs.com/2021 ... storation/

It includes tripler replacement, with reference to this thread on Stardot for sourcing: viewtopic.php?t=3999

I have no experience of Cub refurbishment myself I'm afraid so can't help with the specifics. I'm sure you are already aware, but please take all necessary safety precautions when taking the back off a CRT.
User avatar
ChrisJC
Posts: 46
Joined: Sat Jan 16, 2021 2:01 pm
Contact:

Re: Microvitec Cub goes 'whistle warble click click'

Post by ChrisJC »

Thanks. I hadn't seen that article.

I have made myself a discharge lead for the CRT - 10x 1Meg resistors in series. I am grounding the high voltage connection with that. So far so good!

Chris.
User avatar
ChrisJC
Posts: 46
Joined: Sat Jan 16, 2021 2:01 pm
Contact:

Re: Microvitec Cub goes 'whistle warble click click'

Post by ChrisJC »

OK, so the monitor is now in good working order.

I changed the Tripler, and that got rid of the clicking noise and the visible artefacts on the display.
However the warbling became a shrieking noise.
It changed as I poked things with a screwdriver, but pretty much anything I poked changed it's tone, including just flexing the PCB.

So I changed the Line Output Transformer T203 (no change), Width L202 (no change), T202 (no change), and finally Linearity L203, which silenced it.

My logic was that the noise was caused by an inductive part, so I just worked through them all one by one.

Chris.
philb
Posts: 384
Joined: Sat Aug 05, 2017 7:05 pm
Location: Cambridge, GB
Contact:

Re: Microvitec Cub goes 'whistle warble click click'

Post by philb »

Good work!
Post Reply

Return to “other vintage hardware, software and languages”