Re: Commodore 1084S monitor

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Did you honestly think that replying to an 18 year old posting was likely  
to get you anything more than insults?

Idiot.


Re: Commodore 1084S monitor
snipped-for-privacy@gmail.com says...
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It's been over 17 years since the original message was posted, so it's  
unlikely that anyone remembers the result even if it did get fixed.

What have you tried so far to fix or narrow down the problem, if  
anything?

It sounds like some kind of ghosting or ringing; is there a picture you  
could upload anywhere (Imgur or similar) so we can see what it looks  
like?

I'd start by swapping the video cable and also trying a different video  
source, just to make sure it really is the monitor at fault. Then I'd  
replace all electrolytic capacitors on general principle. These monitors  
are decades old and there are probably multiple caps that have gone out  
of spec by now, so just doing the whole lot can save multiple rounds of  
troubleshooting.

There's a service manual for this monitor available at  
http://www.zimmers.net/anonftp/pub/cbm/schematics/monitors /. The scan  
quality is poor, but it's certainly better than nothing.

Rayner

--  
Big-8 Management Board: https://www.big-8.org
Homepage: http://magic-cookie.co.uk

Re: Commodore 1084S monitor
On Monday, January 18, 2021 at 2:55:52 AM UTC+2, Rayner Lucas wrote:
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Hi Rayner,

Firstly just wanna say to the Google Groups Einstein that the 18 year period doesn't matter as long as the problem was solved and the guy is still around on this earth. The Commode/Amiga retro-scene is very much alive.

Now I have posted lots of pics and info in this thread. I have already recapped the monitor and done a lot of measurements.

https://www.edaboard.com/threads/commodore-1084s-monitor-with-faint-vertical-lines.396322/

I thought I'd also ask here as Alex faced the exact same problem.

Thanks for your time Rayner.

Re: Commodore 1084S monitor
snipped-for-privacy@gmail.com says...
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vertical-lines.396322/
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It's odd to see such an old thread get resurrected, but it is still a  
relevant post even if the original participants are no longer reading,  
so in this case I don't think it's anything to get worked up about.

I see from that edaboard thread that you've already tried the most  
likely solutions :-(

The slowly drifting *horizontal* lines you mention sound like hum bars,  
i.e. excessive voltage ripple from the power supply making its way onto  
the display. If this is the case you'd see two bars on screen at once  
(100Hz ripple from a full-wave rectifier, on a screen with 50Hz vertical  
refresh) Again, by far the most common cause is a bad filter capacitor  
in the low-voltage power supply, but there can be other components at  
fault. See https://www.repairfaq.org/sam/monfaq.htm#monrwphb

If you have access to an oscilloscope, you might want to check the  
outputs of the power supply for unusually high ripple. In particular,  
the output of the 12V DC regulator (IC403) ought to look nice and  
stable, as the regulator should smooth out whatever makes it past the  
filter capacitor.

Obligatory safety note: be very careful and don't work alone, these  
things have some nasty voltages inside them (including that 125V DC  
power supply output). I highly recommend the safety guidelines at  
https://www.repairfaq.org/sam/monfaq.htm#montrbs

Rayner

--  
Big-8 Management Board: https://www.big-8.org
Homepage: http://magic-cookie.co.uk

Re: Commodore 1084S monitor
On Tuesday, January 19, 2021 at 1:52:36 AM UTC+2, Rayner Lucas wrote:
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thanks for all your efforts Rayner. I am using a 1:1 isolation transformer  
when I power up the monitor and I do have an oscope. Ill test the PSU altho
ugh the lines are many more than two.. maybe 7-8 drifting to the bottom of  
the screen. Thing is that there are brand new caps everywhere.

I read around the internet and there was this thread and just one more guy  
with same monitor, same issue. He told me on eab boards via private message
 that his monitor is with an expert at the moment.

it definetely looks like some harmonic but my knowledge in CRTs is very lit
tle at the moment - learning every day.  





Re: Commodore 1084S monitor
snipped-for-privacy@gmail.com says...
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Okay, if there are 7-8 lines it's not mains frequency. I'd say it's  
still worth checking the PSU output voltages for stability, though - it  
will help to know whether you can rule that section out or not.

The number of horizontal lines suggests the unwanted oscillation has a  
350 - 400Hz component, which might be a helpful clue.

If investigating the PSU doesn't reveal anything, here's how I'd look at  
it. You've got a scope and a schematic annotated with expected voltages  
and waveforms. The problem shows up on the display, therefore it must be  
present among the signals and voltages that go to the CRT and deflection  
yoke. If you can figure out which one(s), you can then trace it back to  
the origin from there.

It seems highly unlikely to be anything to do with the EHT or the focus  
grid voltage, which is good because those are the ones I'd least like to  
be messing with.

It doesn't look much like a deflection problem either, as from the  
pictures on the edaboard thread I can't see any actual distortion to the  
image on screen.

As far as I can see, that mostly just leaves the:

+12V line
+125V line
-20V line
RGB signal lines

going to the CRT neck board as the likely candidates.

The safety guidelines at  
https://www.repairfaq.org/sam/monfaq.htm#montrbs include some advice for  
staying safe when investigating a running monitor; I particularly  
recommend the bit about only ever connecting/disconnecting test leads  
when the monitor is unpowered and unplugged.

Let us know if you manage to narrow it down.

Rayner

--  
Big-8 Management Board: https://www.big-8.org
Homepage: http://magic-cookie.co.uk

Re: Commodore 1084S monitor
You do need to know that the position of Village Idiot is occupied by an Australian at this time. Much as you might wish to compete, your status will remain "incurably stupid", only. You may re-apply should the incumbent leave.  

Re: Commodore 1084S monitor
On Monday, January 18, 2021 at 4:48:11 PM UTC+2, Peter W. wrote:
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Get a life Peter instead of running stupidity contests in Google groups especially when you are the undisputed heavy weight champion. No way for the rest of us to win.

Re: Commodore 1084S monitor
On Monday, January 18, 2021 at 1:24:24 PM UTC-5, snipped-for-privacy@gmail.com wrote:
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George:

Then you are in full competition with Phil for the position? He may be relieved to know that.  

Re: Commodore 1084S monitor
On Monday, January 18, 2021 at 9:04:00 PM UTC+2, Peter W. wrote:
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you re not funny dude

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