Philips CM8833 colour monitor problem high pitch whine noise

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Chandler
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Philips CM8833 colour monitor problem high pitch whine noise

Postby Chandler » Wed Dec 30, 2009 3:55 pm

hi all

and a happy new year to all fellow Atari people :)

i have a Philips CM8833 monitor which has the scart lead connection at the rear

anyway when i switch it on it just makes a high pitch whine noise, dark screen - nothing else

when i switch it off it takes a while for the whining noise to go as though it's an old hard drive spinning down!

i'm guessing this is a flyback transformer problem or tube prob??

if anyone can help then please do

thanks

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alexh
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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby alexh » Wed Dec 30, 2009 6:00 pm

Broken LOPT nothing you can do to repair it. You'll need a replacement but in reality you're not going to get one at an economically viable price.

If you're very very lucky your local TV repair company *may* have a spare in their box-of-bits. Get out yellow pages and phone around.

Look on eBay for a replacement local to you and then bin the old one.

Chandler
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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby Chandler » Wed Dec 30, 2009 8:41 pm

thanks

yeah i kinda thought it was the LOPT/flyback transformer so i'll be taking it to the tip sadly :(

also i notice the power LED does not illuminate - could it be a power supply issue?

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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby Womble » Sun Jan 03, 2010 11:16 pm

They are not that expensive or hard to come by as you might think, especially if you factor in postage for any new monitor purchase, far cheaper to ship a 250g LOPT than a 5Kg monitor.

CM8833s are usually the same chassis as the Commodoer 1084 monitors and the most common LOPT for thoses is HR7533 which is 15 quid from

http://www.elclondon.co.uk/acatalog/Onl ... R_147.html

The monitor is probably worth saving if its in good physical condition, there are a lot of tatty yellowed ones out there and a new LOPT will give it another decade or two of life, I fixed up my trusty 1084 that I use as my RGB monitor on my arcade test bench

http://www.aussiearcade.com.au/showthread.php?t=17939

These monitors pop up on ebay quite regularly for a fiver or so, but postage is extortionate for monitors so a new LOPT was actually a cheaper option for me as they were never in my area.
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alexh
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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby alexh » Mon Jan 04, 2010 1:04 pm

Just wait until there is one local to you. Or a 14" portable with SCART. I bet you don't have to wait more than a month.

Nice thread above though. I like the idea of fixing these buggers but it is beyond most and dangerous. BUT the availability of parts means that your local TV repair guy will be able to fix it.

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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby Chandler » Mon Jan 04, 2010 11:28 pm

thanks for your replies guys

would a dead LOPT result in the power LED not illuminating though?

i now know it's not the PSU as i swapped it with a working one and still the same, so it could still be the LOPT or maybe something else on the board

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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby Womble » Tue Jan 05, 2010 9:34 am

Yes it could well, depends on which taps are shorted and what effect it has on the main power rails. Another issue with the commodore monitors is that the power switch is actually 2 in one and often one side dies so part of the monitor isn't getting powered up, worth checking too.
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Chandler
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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby Chandler » Tue Jan 05, 2010 12:19 pm

Womble wrote:Yes it could well, depends on which taps are shorted and what effect it has on the main power rails. Another issue with the commodore monitors is that the power switch is actually 2 in one and often one side dies so part of the monitor isn't getting powered up, worth checking too.


well it's not the power switch as i said i swapped the psu and it's still the same

the psu and power switch all come together on these things

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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby 1024MAK » Wed Jan 06, 2010 12:49 am

Chandler wrote:thanks for your replies guys

would a dead LOPT result in the power LED not illuminating though?

i now know it's not the PSU as i swapped it with a working one and still the same, so it could still be the LOPT or maybe something else on the board


In most CRT TV's and monitors (VDU's) the main power supply feeds the LOPT circuits. The LOPT has multiple secondary windings, some of which supply the rest of the circuits with power. So if there is a problem with either the transistor that controls the LOPT, or the LOPT itself, the rest of the circuits will not be powered. It is likely that the power LED is fed from one of these supplies.
Follow the advice given above and take it to a local TV repair shop. They will be glad for the business and will be able to fault find this kind of problem much better than we can here :cheers:
Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (nearly forgot the Psion's)

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Womble
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Re: Philips CM8833 colour monitor problem high pitch whine noise

Postby Womble » Wed Jan 06, 2010 3:04 am

Trouble with paying for someone elses time with this retro gear is that the final bill will far exceed the replacement cost of the unit, its barely worth repairing due to the cost of the replacement part, so unless its in especially good condition or is considered an old friend it is never going to be economically viable to repair. Add to that the fact that the vast majority of TV repair shops went bust in the last ten years you may find that your nearest one is not exactly local. People tend to use the death of a CRT as a great excuse to buy a big flat screen TV, and they are not repairable beyond just swapping the 2 or 3 PCBs that are in them, you cant actually get spares for modern set, the manufacturers spares depts will now only replace entire boards, further pulling the rug from under anyone trying to run a business in TV repair.

A shut down unit and a squeeling noise is almost always a LOPT fault, simplest way to find out is to take the LOPT out and measure the resistance between the primary and secondary taps, anything other than a total open circuit is a big fat fault on the LOPT.
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