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Old 3rd Jun 2019, 11:59 pm   #1
WizRider
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Default Help repairing a Commodore 1084S CRT monitor

Hi all.

I've just bought a Commodore 1084S monitor and it has been damaged during delivery.

Everything was fine for a moment or two after powering it on but after a few seconds the picture went like the attached image.

I'm a real newb when it comes to electronics but I think it's called partial vertical collapse.

Is there anyone that can help me get the monitor working again? Happy to pay for people's time of course.

Thanks!
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Old 4th Jun 2019, 12:41 pm   #2
GadgetM
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Default Re: Help repairing a Commodore 1084S CRT monitor

As it may have been mistreated during postage I suspect that you may have cracked solder joints on or near the frame IC. Take a look at the underside of the whole board with a magnifying glass and re-solder any joints that look suspect. It's not really frame collapse there, more a vertical linearity issue. Good luck!

...You may also want to check for any electrolytic capacitors with bulging tops as they will need replacing.
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Old 4th Jun 2019, 1:05 pm   #3
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Default Re: Help repairing a Commodore 1084S CRT monitor

If you look at the raster you can see it is a lot more than a vertical scan issue. The scan width is reduced. The vertical scan shows distortion of the trace (abnormal linearity) and there is cross over distortion in the scan accounting for the bright horizontal line through the center of it.

So this information suggests that there is neither a fault in the vertical scan circuits, or the horizontal scan circuits for that matter (unless you want to postulate two simultaneous faults in the H & V scan circuits, which is far less likely).

One fault more than likely links the two defects in the H and V scan. It pays to remember that in the case of the H scan, the scanning width is directly & linearly proportional to the power supply voltage to the H scan stages.

I think there is a power supply fault and in a monitor of this age, likely there are electrolytic capacitor issues in the power supply. However, as noted it is possible there are track fractures if there has been shipping damage to this unit.
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Old 4th Jun 2019, 3:36 pm   #4
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Default Re: Help repairing a Commodore 1084S CRT monitor

The fact that it did work briefly tends to suugest it's not capacitor problems - these were pretty reliable. It's time to get a magnifying glass out and look over the print. Start with the heavy components, such as the line transformer, then look at items with heatsinks. I tend to agree thet we have a power supply issue here, so looking at the chopper transformer's connections might prove fruitful.
As you say you're new to this, please bear in mind there can be high voltages lurking around, even with the set off. You might prefer to seek help - there are lots of people on this forum who'd be happy to assist in repair..
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Old 4th Jun 2019, 6:11 pm   #5
WizRider
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Default Re: Help repairing a Commodore 1084S CRT monitor

Thanks so much for the info guys.
From my non-technical viewpoint I also think it's related to a cracked solder joint for what it's worth (not a lot I know!).

As Welsh Anorak says though, I'd rather seek help from someone on here that can assist in the repair. Are there any kind volunteers? I'd be happy to pay for your time.
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Old 4th Jun 2019, 6:31 pm   #6
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Default Re: Help repairing a Commodore 1084S CRT monitor

In that case, make a post in this section: https://www.vintage-radio.net/forum/...play.php?f=145.
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Old 4th Jun 2019, 7:30 pm   #7
WizRider
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Default Re: Help repairing a Commodore 1084S CRT monitor

Will do AC/HL.

Thanks for the help everyone.
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Old 4th Jun 2019, 8:52 pm   #8
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Default Re: Help repairing a Commodore 1084S CRT monitor

Quote:
Originally Posted by WizRider View Post
Hi all.

I've just bought a Commodore 1084S monitor and it has been damaged during delivery.
Is there any evidence for that, for example a damaged case?

I'm thinking that it might have just developed a natural fault, as vintage technology does.
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Old 4th Jun 2019, 9:55 pm   #9
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Default Re: Help repairing a Commodore 1084S CRT monitor

My feeling is as per Glyn's, that something heavy and attached to the PCB only by old, soft, solder got shaken around a bit in transit. I'd be looking for ring shaped cracks in the solder around the pins of the Line Output transformer especially.

It may, however, be worth wiggling the front and rear external adjustment controls back and forth a little bit just in case they have gone a bit noisy / intermittent. On my very similar Philips monitor some of these external controls govern hold / height / width and position.
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Old 4th Jun 2019, 10:01 pm   #10
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Default Re: Help repairing a Commodore 1084S CRT monitor

The OP has also posted here:-

https://www.vintage-radio.net/forum/...d.php?t=157061
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Old 5th Jun 2019, 2:44 am   #11
Terry_VK5TM
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Default Re: Help repairing a Commodore 1084S CRT monitor

When I was repairing these way back when, a common problem was cracking of the pcb and tracks around the flyback (EHT) transformer.

Don't run it for too long in this condition, depending on what has broken, it can take out the transformer, which are like hens teeth these days.
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Old 5th Jun 2019, 9:03 am   #12
dominicbeesley
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Default Re: Help repairing a Commodore 1084S CRT monitor

When you say it "works briefly" do you mean when the computer first starts - could this be the computer running in a display mode not suited to the monitor once it has booted? I'm not sure how screen modes are configured on an Amiga but worth a check before you start chasing hardware faults.
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Old 7th Jun 2019, 4:25 pm   #13
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Default Re: Help repairing a Commodore 1084S CRT monitor

I think the amiga is fixed at 625/50 composite video, at least mine is, no mode switching possible AFAIK
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Old 10th Jun 2019, 10:48 am   #14
dominicbeesley
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Default Re: Help repairing a Commodore 1084S CRT monitor

Fair enough, I thought the newer models offered multi-scan modes too. It was just that that picture looked like the results on my CRT monitor did when fed a non-standard mode from my Archimedes when I used to play around with over-scan modes and get the sums wrong!
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Old 13th Jun 2019, 4:47 pm   #15
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Default Re: Help with Commodore 1084S near Northampton

Looking at the schematic ..
from what I can see some of the Line output (horizontal scan) is applied to the frame or field scan circuitry..
I guess for raster correction ? of some sort ..
If I were looking for apcb daage or cracks I would start at pin 7 of the line flyback transformer and check for damge to traces or components as the chain of parts heads to the frame generator chip TDA2653A.
I suggest this only because not only is the frame or field linearity grossly affected ...but also Line output (width) has been affected (reduced) looking at our photo.
rgds and good hunting
VS
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