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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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10th Jun 2019, 8:18 pm | #1 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Philips CM11342/55G video monitor
Hi, hopefully someone can help I have a RGB Philips video monitor, and it stoped working. All it does now when I turn it on is give out a high pitched whistle. when I turn it off the whistle drops in pitch then fades off that’s all it does?!. Can anyone give me a starting point of where to start looking??
Dave
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10th Jun 2019, 9:13 pm | #2 |
Heptode
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 640
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Re: Philips video monitor
Do you have a model number? The fault you're describing sounds very much as though this could be a CM8833 and sadly the LOPT is a well known cause of this.
John. |
10th Jun 2019, 9:23 pm | #3 |
Nonode
Join Date: Mar 2010
Location: Sunderland, Tyne and Wear, UK.
Posts: 2,473
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Re: Philips video monitor
Yes agreed the Lopts on these and Commodore branded versions were a well known cause of this fault, oddly we used to be able to buy the Philips original transformer cheaper than any of the replacement branded ones.
I can remember buying original Phillips ones for about £6 plus VAT trade, some of the copies could be three times as much!, usually it is the other way around. Edit: IIRC there were about three different common Lopts across the various model ranges, the AT number on the transformer was most important when ordering replacements, because of course they all looked visually alike.
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I don't suffer from Insanity. I enjoy every minute of it. Last edited by Red to black; 10th Jun 2019 at 9:29 pm. |
10th Jun 2019, 11:37 pm | #4 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
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Re: Philips video monitor
I would hapily guess that it is a Phillips grey Lopt.
They were just as bad in VGA screens of quite a few makes. |
11th Jun 2019, 9:48 am | #5 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips video monitor
Hi the monitor is the CM11342/55G , I’m about to take the back off!!!
AT2079 is what’s on the LOPT
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11th Jun 2019, 12:40 pm | #6 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,185
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Re: Philips video monitor
That's not the full number, only the basic style.
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13th Jun 2019, 11:53 am | #7 |
Dekatron
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,884
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Re: Philips video monitor
The AT2079 used to fail in large numbers in many Philips TVs and monitors of that period. As Maarten says, the rest of the number is vital to get the correct LOPT. HR Diemen is your best bet.
CPC used to have their own line of LOPTs which were a complete failure. The one for the Philips monitors connected a HT pin to chassis! Cutting this off got things going, but the secondary voltages were clearly not right. |
29th Jun 2019, 11:25 am | #8 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips video monitor
So so far I’ve checked the big transistor that drives the LOPT and it’s ok!?
Also checking the switching transistor in the power supply and that’s still a transistor as well... any thing else to look for?
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29th Jun 2019, 8:23 pm | #9 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips video monitor
Just uploaded some photos of the board !!
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29th Jun 2019, 8:58 pm | #10 |
Pentode
Join Date: Aug 2008
Location: Taunton, Somerset, UK.
Posts: 135
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Re: Philips video monitor
In a repair tips book I have it says to check R3412 (33K Ohms) for open circuit.
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29th Jun 2019, 9:24 pm | #11 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips video monitor
Hi so you mean it could be a resistor!!!! Hope it is the one that’s problem!!
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29th Jun 2019, 9:26 pm | #12 |
Heptode
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 640
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Re: Philips video monitor
Isolate pin 3 of the LOPT, if the squealing stops then it's highly likely to be faulty. From your picture it looks to be an AT2079/37591, it's equivalent is an HR7533.
John. Last edited by jayceebee; 29th Jun 2019 at 9:34 pm. Reason: more info |
29th Jun 2019, 11:33 pm | #13 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips video monitor
Ok checked the 33k resistor and it’s fine I replaced it anyway lol.. checked the transistor near it that was fine ... could the 7412 regular be a problem as was thinking of pulling that out to check... if not how do I find out witch pin is pin 3 to isolate? And il try that next!!!
Dave.
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29th Jun 2019, 11:35 pm | #14 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips video monitor
Ok iv looked at the photo now I can see pin 3 .!! Would de soldering it be ok and some how put tape round it? To isolate?
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30th Jun 2019, 12:40 am | #15 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
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Re: Philips video monitor
Have you checked the line output transistor and fly back diode are not short circuit?
They will cause that symptom. Those grey line output transformers usually don't completely trip the mains regulator in the way yours is doing. |
30th Jun 2019, 9:01 pm | #16 | |
Heptode
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 640
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Re: Philips video monitor
Quote:
It would be good to know the resistance between pin3 and it's solder pad to chassis before and after isolating it. Might also be prudent to check the blue tuning capacitor next to the LOPT for any signs of dry joints or arcing damage. This can show as a bulge on the capacitor body. |
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30th Jun 2019, 10:51 pm | #17 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips CM11342/55G video monitor
Iv checked to lopt drive transistor it’s ok where do I find the diode?
Dave
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1st Jul 2019, 12:20 am | #18 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
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Re: Philips CM11342/55G video monitor
Just follow the tracks from C and E of the transistor.
What is the part number of the transistor? The capacitor should also be in the same position. |
1st Jul 2019, 12:42 am | #19 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,185
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Re: Philips CM11342/55G video monitor
At this point, I would first test the power supply with a light bulb as a load. I don't have the schematic handy, but take care to interrupt the supply to the line output stage before testing.
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1st Jul 2019, 11:23 am | #20 |
Tetrode
Join Date: May 2007
Location: Downham Market, Norfolk, UK.
Posts: 83
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Re: Philips CM11342/55G video monitor
So I’m looking at the pin out of the LOPT that’s on this post would it be pin 10 I disconnected and connect the light bulb to instead? For testing the power supply?
I am a bit of a novice at repairing CRTs sorry.. Dave.
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