Author Topic: Hello! / New User - CTM644 problem & CPC 464 whining problem  (Read 4714 times)

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Offline bleeper

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Hi there, just picked up a CPC 464 for the first time in 15 years, and have been having fun but there are a few problems with my system :
 
1. CTM644 - picture is generally clear and colourful but there are several bright horizontal lines which occupy the top 1" of the display, only when there are borders. On games / programs that have black borders, this problem goes away. V-Hold and H-Hold do not cure the problem. A quick Google says this might be a vertical retrace issue but I wondered if anyone else has had this specific on their monitor?
 
I am hoping this is something I can easily adjust internally or it's just 1 culprit capacitor, or is it a symptom of something worse?
 
2. The CPC itself makes a fairly low, but audible whine. Like interference or something. It all seems to work fine and loads tapes fine so it's not critical I sort it, although it would be nice :)
« Last Edit: 15:30, 07 June 10 by bleeper »

Offline Gryzor

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Hello mate, welcome to the forum and the scene in general! It always feels great to pick one up again, doesn't it? :)

Concerning your issues; there are far more knowledgeable persons than me here, so just hang on and someone will narrow it down for you, but in both cases it does sound like a capacitor issue to me... How loud is the whine anyway? I mean, I think there is supposed to be some!

In general, changing capacitors in old machines is usually a good idea. I've done it with some of my oldest machines (from the 70s and early 80s) and the difference is very visible!

Offline Bryce

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Good morning Bleeper,
            a few questions to your issues:

Is the whining just generally coming out of the keyboard and varies depending on what the processor is doing? If so, then welcome back to 1984, this is perfectly normal for the CPC.

Concerning the monitor problem, this is a bit more fifficult to diagnose, but usually easy to solve. You didn't say what colour the stripe(s) are, maybe the easiest thing to do is take a foto (640x480 resolution should be enough) and post it to this thread (click the "Additional Options" below the text input field to attach the file, JPG or PNG preferrably). Then it's easier to tell you what needs replacing. But you are correct, it's most likely just a capacitor, not some unobtainable custom part, so it should be a quick fix.

Bryce.

Edit: Also important: If you leave the CPC running (without loading any programs), do the lines eventually fade, or do they always stay bright?

Also, how much electronics knowledge do you have = A) I've built my own low-orbit satelite control system, B) I can recognise components and know what they do, or C) What's a soldering Iron?
« Last Edit: 12:39, 08 June 10 by Bryce »

Offline Cholo

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Cant help you much with the errors im afarid, but do be carefull before attempting any kind of repair. Especially be carefull and dont touch inside the monitor unless you dont know what to do.

Offline bleeper

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Hi everyone, thanks for the welcoming replies :) i am really glad i decided to get her up and running again and to stumble upon this active and friendly community.
 
Anyway, the whining has stopped bothering me as much now. In fact, I think it's gotten quieter, perhaps the parts have 'warmed up' now. All part of the charm hey  ::)
 
Unfortunately, the monitor lines are still there no matter how long I leave it on for. They seem to take on the colours of whatever the border may be - i.e. if yellow i'd get yellow stripes. I know it's not the CPC causing this as I've tried it on another CTM and its perfect. And as I said, if the borders are black, as in most games, the stripes disappear. It seems to only affect the overscan area (if that's the right term?)
 
As for my technical knowledge, I am competent at soldering, discharging, etc, and following instruction, but not really diagnosing or knowing why I'm soldering this or that. The low-orbit satellite control system is next on my list, obviously... ;)
 
Maybe I need to decide if it's economical to fix this or not... I would actually prefer a green screen anyway since that's what I used for years till I 'upgraded'. It would be fun to give it a go before giving up, however.
 
P.S. the dark lines on the pics are just my camera.
« Last Edit: 02:17, 09 June 10 by bleeper »

Offline MacDeath

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Hi and welcome back to the 80's.

Did you open your CPC ?
Often a lot of dust can be find inside those old machines.
Removing it is always good.


Also : those are old machine, and we must remember those were done with cheap of the shelf components.

The power supply suffers from time, creating a lot of parasits, as the monitor is also prone to get some dust.

So :
--clean the plugs.
--open the CPC just to look if there nothing obvious : Capacitors from the 80's were prone to explode...
--concerning the monitor, it's a bit more dangerous to open it, as TV features lots of dangerous charged capacitors...but if done with care, why not.

http://en.wikipedia.org/wiki/Capacitor
http://en.wikipedia.org/wiki/Capacitor_plague

So just inspecting dust, connections and faulty capacitors is a good start.


To remove dust, prefer dry air canisters, but just blowing at it an do it well, if not recommanded. A paint brush may be fine too...yet not recommended too.



For your lines : My CPC monitor is prone to get the same when the external 3"1/2 DiskDrive I use with my CPC6128 (the qwerty one) is activated...
It was a shitty montage my brother did in the past, and he simply derivated the +5V supply, adding a plug on the CPC...

Are your "clear lines" stable ? or are they moving randomly ?

Also you told us it happen when a coloured border is on and disapear when the border is black.

Have you tried to change the colour of the border in Basic ?
Or changed the video mode in basic ?

not sure, but "Mode0", "Mode2", border (enter colour number) and so on...this would be easy to verify.

But yeah, this seems to come from the monitor, perhaps not well synchronised at the first raster line.

One thing may be to try "overscan" vertical full screen games.

Such as Konkey Dong (pun), Arkanoids or Ghouls and Ghost.
Those use the first rasterline, but also feature a black border...
Would be interesting to see if this produce the parasites.

Also check every border colours...


And to be honest, unless you are a retro tubeTV hobbyist... the best would be to simply find another Monitor, but availability may depend of where you live.
Easier in France...


Have you tried to modify the setting of the "synchronisation potentiometer" ? (don't know its real name).
That is the potentiometer at the rear side of the Monitor.
 
« Last Edit: 09:04, 09 June 10 by MacDeath »

Offline Devilmarkus

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Hi bleeper,
seems, that your V-position is adjusted bad in your monitor.
Perhaps a potentiometer, which died, or a capacitator.
Not too hard to fix.
When you move V-position too high, those lines also appear on a TV.

BTW.: Welcome to our forum!
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Offline Bryce

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Hi Bleeper,
           the lines on your screen are a classic example of vertical foldover and shouldn't be too difficult to fix. Firstly as mentioned above, BE CAREFUL when you open a monitor, don't touch any contacts if you haven't discharged them beforehand, the circuit will still have relatively high voltages (400V) at several points even days after unplugging it. But, you say you know how to discharge, so I assume you've done similar work before and know what you are doing. If not check the web for methods to discharge the capacitors DON'T just short-circuit them!

Now to the problem: The CTM644 uses an LA7830 vertical scan driver chip (not transistors as often used in cheap TVs). This is the chip with (7) pins on only one side and it's bolted to a heatsink. When you look into the back of the monitor, it should be on the lefthand side at the rear of the PCB (front of the monitor). It's timing is controlled by several large capacitors and a few resistors. You may just have a dry joint somewhere in this area (See picture below with red square marking the area), so check and re-solder anything in this area that looks dodgy. It may even be dust full of moisture under the PCB, so remove any dust too. If it's neither of these, then it is most likely that one of the two capacitors shown below (C424 / C425) has reached it's end of life. There won't be any external signs that it's broken (ie: raised lid or blackness etc), because it has dried out, not overheated. Both of these are electrolytic capacitors (the one's that look like little blue/black cans). Replace them with the same value (and voltage) and remember that they have a plus and minus pole, so make sure you solder them in the right way around. That should solve your problem. If not, then there's always the chance that the LA7830 is internally damaged, but this is fairly unlikely, and a real pain if it is, cos I doubt they are easily available today.

And if you really want to go back to green screen, I'll gladly swap my GT65 for a CTM644, if you're not too far away :)

Let us know how it goes,

Bryce.

P.s. @MacDeath: The line problem you're having with the external floppy is a voltage drop problem within the CPC. Solder a large electrolytic capacitor  (about 1000µf 16V should do) across the pins of the 5V output plug that your brother added and the problem should go.
« Last Edit: 11:45, 09 June 10 by Bryce »

Offline MacDeath

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Quote
MacDeath: The line problem you're having with the external floppy is a   voltage drop problem within the CPC. Solder a large electrolytic   capacitor  (about 1000µf 16V should do) across the pins of the 5V output   plug that your brother added and the problem should go.
yeah, I knew this was a Voltage drop.
(Captain Obvious was here)
But I didn't knew if it was in the CPC or in the Monitor (after all, the monitor is also the powersupply and I didn't tested/investigated this further.)

Thx for the solution anyway...
Will check for this.

Offline Bryce

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I had exactly the same problem with my CPC when I connected my 3.5 drive to the 5V rail. The outputs to the monitor were dropping too low and the screen had flickering lines that were synchronised with the head reading :) The capacitor solved it though :)

Bryce.

Offline bleeper

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Thanks for that diagram Bryce, once I have a spare couple of hours I'll try it out. Promise I'll be careful. :)
 
I wouldn't mind swapping it for a GT65 but sadly I'm quite far from St.Lucia here in sunny England!

Offline Bryce

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:D I'm not really in St. Lucia, I just liked the flag. I'm in Germany, but that's too far too :(

Bryce.

Offline Gryzor

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Then make it your avatar! You're abusing the system :)

Offline Bryce

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As I use the "ModernDark64" skin, I don't see the flags anyway, just the letters LC :(

Bryce.