CRT repair

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VincentVega
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CRT repair

Post by VincentVega » Sat Aug 25, 2018 2:30 pm

Can anyone recommend a repairer for CRT screens that is within easy travelling distance from the West Midlands? After a long time searching, I finally managed to get hold of a Philips BM7522 amber monitor, just like the one I had when I was a boy.

Initially, the monitor worked fine, but it seems to have developed a fault. If I press the power switch at the front, there is a brief amber flash on the screen (roughly the width of the screen, and centred vertically and not very tall). The power LED doesn't turn on either, worryingly. I did take the back off the monitor to see if there were any scorched areas, and I can't see any; the fuses I could see didn't look to have blown either. That's the limit of my diagnosing skills, especially with high voltages inside the case.

I'd like to try and get this thing repaired, as they don't come up on eBay very often, and it's in very good condition externally, despite being 30 years old.

Prime
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Re: CRT repair

Post by Prime » Sat Aug 25, 2018 4:21 pm

There's a TV repair shop near me in Radford Coventry that repaired our CRT TV a few years back.

FM TV Services.
189 Cheveral Ave
Radford
Coventry
CV6 3EN

Phone 024 7660 1093

Might be worth giving them a call.

Cheers.

Phill.

Kazzie
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Re: CRT repair

Post by Kazzie » Sat Aug 25, 2018 5:00 pm

VincentVega wrote:
Sat Aug 25, 2018 2:30 pm
Can anyone recommend a repairer for CRT screens that is within easy travelling distance from the West Midlands? After a long time searching, I finally managed to get hold of a Philips BM7522 amber monitor, just like the one I had when I was a boy.

Initially, the monitor worked fine, but it seems to have developed a fault. If I press the power switch at the front, there is a brief amber flash on the screen (roughly the width of the screen, and centred vertically and not very tall). The power LED doesn't turn on either, worryingly. I did take the back off the monitor to see if there were any scorched areas, and I can't see any; the fuses I could see didn't look to have blown either. That's the limit of my diagnosing skills, especially with high voltages inside the case.

I'd like to try and get this thing repaired, as they don't come up on eBay very often, and it's in very good condition externally, despite being 30 years old.
I can't consider myself an expert on CRTs, but this fault sounds similar to one on my colour Phillips monitor. In my case, a latch on the mains switch at the front had worn away, so it would only power up if you pressed and held the power button. Replacing the switch solved my issue.

Even if your monitor has a different fault, it sounds to me like a basic fault that affects the whole monitor. so it should be a relatively easy fix. Here's hoping that the professional in Coventry comes to the same conclusion.
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Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
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VincentVega
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Re: CRT repair

Post by VincentVega » Tue Aug 28, 2018 9:16 am

Thank you both for the responses. I sent FM TV an email, but unfortunately they don't repair CRTs any more.

VincentVega
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Re: CRT repair

Post by VincentVega » Tue Sep 18, 2018 8:16 pm

A quick update on this. I sent a few emails around to various other places I'd found on the internet that said they repaired CRTs. Some of them replied (and said "no can do"), others didn't bother.

I was about to post in the Vintage Radio "services wanted" forum, but decided to check the monitor was still kaputt first. I gingerly set it up and pushed the power switch on the front of the monitor. Much to my surprise, the power light came on and stayed on. I quickly turned it off, dashed upstairs to grab an Electron and connected them together. My second push of the power switch was just as successful as the first.

I have no idea why it should suddenly start working. Dry joint, perhaps? It's been sitting downstairs in a reasonably warm room for a few weeks - when I tried it before, I was outside (in case anything went bang). I'll probably set it up next to my main desk and give it a soak test for a few hours.

Weird.

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1024MAK
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Re: CRT repair

Post by 1024MAK » Tue Sep 18, 2018 10:29 pm

Could be a dry joint. Could be a poor plug or socket connection. Could be the contacts in the on/off switch. Could be the device that controls the demagnetisation of the screen. Could be a large electrolytic capacitor in the main power section.

Mark

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sbadger
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Re: CRT repair

Post by sbadger » Sun Sep 23, 2018 9:10 am

As someone else said, the power switch on philips monitors is flakey (the internal latch starts to fail) and does does like yours is starting to go, you can buy new switches (but require discharge, dismantle and desolder) other people just wedge the switch in with a bit of plastic/lollystick!.
Don't give up though, it will be fixable.
So many projects, so little time...

Kazzie
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Re: CRT repair

Post by Kazzie » Sun Sep 23, 2018 1:10 pm

sbadger wrote:
Sun Sep 23, 2018 9:10 am
As someone else said, the power switch on philips monitors is flakey (the internal latch starts to fail) and does does like yours is starting to go, you can buy new switches (but require discharge, dismantle and desolder) other people just wedge the switch in with a bit of plastic/lollystick!.
Don't give up though, it will be fixable.
That fault has already materialised on my monitor some years ago, and I've already resolved it with a replacement switch.

This new fault certainly allows some power to flow inside, as it's giving a high-pitched whine. (The switch is definitely latching properly.)

Sadly, lack time and tablespace hasn't allowed me to open 'er up and have a look yet.
Last edited by Kazzie on Sun Sep 23, 2018 1:11 pm, edited 1 time in total.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
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sbadger
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Re: CRT repair

Post by sbadger » Mon Sep 24, 2018 8:07 am

From experience high pitch will be either the flyback (LOPT) on the way out or the power transistor, which on philip colour crts i *think* is a BU508A.

The BU508A being quite any easy swap, LOPT a bit more involved, and may as well do all the electrolytic caps while your at it.

*always discharge the tube!*
Last edited by sbadger on Mon Sep 24, 2018 8:10 am, edited 1 time in total.
So many projects, so little time...

VincentVega
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Re: CRT repair

Post by VincentVega » Mon Sep 24, 2018 5:57 pm

Sounds like it would be a good idea to replace the switch. I've used the display a few times since my last post, and it's still working.

Where's a good source for switches? I see that Retroclinic sell some - for the "CM8833, CM11342 and others" - https://www.ebay.co.uk/itm/PHILIPS-CRT- ... SwCcZaS8CA. Will these fit the BM series?

RobC
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Re: CRT repair

Post by RobC » Mon Sep 24, 2018 8:03 pm

I got my CM8833 switches from Donberg.

They have various other switches on their website.

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