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dougal
29th December 2014, 15:02
I've got a Philips CM8833 which used to work perfectly until about a year or two ago.

Rather than throw it away I kept it in my garage. I'd love to fix it but don't really have any experience with repair of CRT's.

The problem is that there is a totally black display. No light, nothing.

The monitor power light comes on and sound works from the speakers but no image.

Beavis
29th December 2014, 15:19
Philips is quite infamous about bad solder joints, so you should check the board first.
When the power is on, and you move your hand close to the screen, do you feel something like hairs getting drawn to the screen or not?
Hard to explain, but I hope you get the drift.:lol:

Marmes
29th December 2014, 21:52
wich monitor is it mk1 or mk2?
if you have a soldering iron, just resolder as Beavis said. If that doesn't work, go to a tv shop repairer, it will be better.

dougal
30th December 2014, 05:26
Its a mk1. Where should I check for cold solder ?

Beavis
30th December 2014, 08:20
Where should I check for cold solder ?

That's easy, everywhere.:D
But check the flyback circuitry first, when there's a bad joint, it will start arcing, and cause more damage.
You didn't answer my question though, is there any HV present?

Oh, and I assume that you already knew that the HV in a monitor can be lethal, but I'm telling you anyway.
And what Marmes said, if you're not sure, or lack some skills, better take it to a repair shop.

roy_bates
12th June 2015, 07:04
did you ever fix this?

can you take the back off and take a picture of the main board from the rear with the tube neck pcb also in shot,if its the same as mine i can take a look at it for you if you send me all the pcb's in the monitor,itll save on shipping.

it can be the mk1 or mk2,it wont matter to me...

give it a few weeks though im recovering from surgery...

dougal
12th June 2015, 07:07
Never really continued on this. I'll try and take a look this weekend and post back :)

GKJetpack
8th August 2017, 17:25
I have the exact same problem... black screen and a whistling noise from the main PCB near the flyback.


I checked the BU508 transistor for short, but it was all good. Then I ordered a replacement of the flyback, got the HR 7506 and after mounting this I got the HV back on.


But, the screen is getting all white and there is a sound of something is getting saturated. ( The tube warm up time is like normal, but the screen is getting all white )


Videosignal is not be shown on the screen. ( can't remember if the sound is good, but I thinks so )


PSU voltages are measured and they are only a little of nominal values.


What am I missing ?

fordav1
12th August 2017, 01:15
I have bought many replacement flybacks over the years and every one has been shipped with the screen control turned up full. That basically over-volts the neck board and tube RGB guns by 2 to 3 times and can blow up the neck board or tube or both. With it up full you'll get a very bright white screen and some HV noise and arcing on the neck board. Turn the screen control pot (on the flyback) all the way down (maximum turn counter-clockwise) then adjust it as required slowly. Usually it only needs a very small turn clockwise and it is enough.
It that doesn't help then you simply have some other issue. You should start by changing all the caps because dry shorted caps can cause many problems. Plus, they are all 30 years old so should be changed anyway. Or pull each one and test it in a cheap chinese cap tester available on the other bay for a few bucks. if changing the caps still doesn't fix it then start looking closer and testing parts (transistors/resistors/pots etc). All those Amiga monitors can be fixed no matter how bad the problem, it just takes time to go through it.