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Old 25th Feb 2021, 4:26 pm   #1
Grimm177
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Default Philips CM8833 Mk I - Suspected LOPT failure.

This is the model with the RGB Scart input. Purchased new in approximately 1989-1990. It was regularly used for 4-5 years before my parents moved, after which it was put into storage (in its original box) in the loft.

I got it down to put into use last summer and although the power button broke soon after, it was seemingly working fine for about 3 months. One evening the picture went out along with the power light and there was a high pitched whine, which I learnt after is most likely failure of the LOPT. From what I've read, along with the power button, a common problem with these and similar monitors.

Although it looks to be a relatively straight forward repair from the videos I've seen (if you're experienced), I'm not sure I'm comfortable attempting it myself as my soldering skills are weak and I'm not sure I fancy using something like this for practice!
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Old 25th Feb 2021, 4:48 pm   #2
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Default Re: Philips CM8833 Mk I - Suspected LOPT failure.

What is your question?

You have an identical thread here:-

https://www.vintage-radio.net/forum/...d.php?t=176932
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Old 25th Feb 2021, 5:07 pm   #3
Grimm177
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Default Re: Philips CM8833 Mk I - Suspected LOPT failure.

Apologies.

I was wondering if there were any simple things I could try to confirm my hypothesis.
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Old 25th Feb 2021, 5:41 pm   #4
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Default Re: Philips CM8833 Mk I - Suspected LOPT failure.

I suggested that the OP posted a request for help so that we could reply to him with suggestions on how he may possibly repair it himself if it is a simple fault.

As the original post was in the other section we cannot reply with suggestions of help as this is forbidden...

Anyway...
Here are my suggestions, keeping it simple...
Firstly check around the panel for bad soldered joints particularly on the LOPT and around it. Check where the scan-coils (on the tube neck) connect to the main panel. then have a look for any capacitors with bulges or other signs of distress.
I don't have any experience of this particular model but maybe others can say if the LOPT is a common failure on this chassis? On some sets you can see when the LOPT has failed as there is a split in the plastic or a melted band around the winding where it has failed.
If these simple checks prove fruitless maybe we can move on to checking the line output transistor if the OP has a multi meter?
Hope this helps and encourages you to have a go... we all started somewhere...

Rich.
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Old 25th Feb 2021, 6:49 pm   #5
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Default Re: Philips CM8833 Mk I - Suspected LOPT failure.

It probably is the LOPT. They often fail with a smell, but the OP doesn't mention this, so it's probably just shorted.
Do you have a multimeter? That would be useful. If you want to repair it yourself, I'd suggest getting one of these:- https://cpc.farnell.com/duratool/d01...olering%20tool
That will get the LOPT out with no damage to the print. Once it's out you can make some simple teats with your meter to see if this is what's failed. A cheap meter and basic soldering equipment will be useful for you.
Otherwise post a message on 'help wanted' and I'm sure there's someone local who could help.
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Old 25th Feb 2021, 8:23 pm   #6
Grimm177
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Default Re: Philips CM8833 Mk I - Suspected LOPT failure.

Thank you both

It did smell somewhat when I first put it back into use but I (perhaps naively) attributed that to aged plastic heating up after 25+ years of not being used. The smell had gone by the time it failed a few months later.

I do have a multimeter, a cheap/basic soldering iron and a solder sucker (not heated). I'm just concerned about either getting a clout off of it, making things worse or possibly both

I wish I could fix these things myself. I also have a couple of early 80's Trinitron's that need attention

Last edited by Grimm177; 25th Feb 2021 at 8:42 pm.
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Old 25th Feb 2021, 8:56 pm   #7
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Default Re: Philips CM8833 Mk I - Suspected LOPT failure.

It's not clear to me if 'LOPT' means Line Output Transformer or Line Output Transistor here. Mind you in my experience failure of the former can damage the latter.

If you can't sort it out yourself and can wait until lockdown is over then I am not that far from you and have a reasonable toolkit including an EHT meter that can be used to safely (for us and for the monitor) the high voltage on the CRT and a ringing tester that will detect shorted turns in the transformer.
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Old 26th Feb 2021, 3:40 pm   #8
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Default Re: Philips CM8833 Mk I - Suspected LOPT failure.

In my experience it's usually the transformer that fails and loads the HT line down, though of course the transistor can do this as well.
I'd take up Tony's offer as he'll be able to tell you at once where the fault is and save you getting unnecessary parts.
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