Author Topic: Amstrad monitor strange behavior  (Read 1424 times)

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Offline Fmtrx

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Amstrad monitor strange behavior
« on: 19:25, 16 August 20 »
Hello all,

I have a main unit CPC 6128, and until recently i had it hooked on a TV with the SCART adapter, and everything worked as expected.
Recently i purchased a CTM 644 monitor that works ok BUT has a strange behavior only at the first time of the day i switch it on:
When i power on the monitor and then the main unit, the main unit does not boot up, no red light is on.
When i switch off main unit and then the monitor and i repeat, then it works. Sometimes it works at the third time.
After this, the system always switches on at the first try during the day.

I have used a multimeter at the output of the monitor to check if the voltage is not high enough during the first start up, but the voltage is ok:
it always reads 5.17 V.

Does anyone know what could be wrong with the monitor? What part needs servicing ?
I am feeling that after sometime, the monitor will stop working.

Thanks in advance
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Offline Bryce

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Re: Amstrad monitor strange behavior
« Reply #1 on: 20:26, 16 August 20 »
Yes, the capacitors in the monitor are at the end of their life and need to be replaced. This is typical behaviour for capacitors that are starting to fail.


Bryce.
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Offline Fmtrx

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Re: Amstrad monitor strange behavior
« Reply #2 on: 08:22, 17 August 20 »
I see, thank you for pointing me to the right direction.
I may come up later in the afternoon with some pictures of the internals of the monitor, i am eager to see what is its condition from inside.

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Offline Fmtrx

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Re: Amstrad monitor strange behavior
« Reply #3 on: 23:05, 17 August 20 »
Hi Bryce,


I opened the monitor and took some photos. It seems i am in bad luck, as i could not find any particular capacitor that had the signs of wear.
I know that they can fail even if they do not show the bulging effect. So this means that i have to replace ALL capacitors in order to be sure that the issue is solved. Right ?


Picture 1 & 2: show the left and right side and the current external state of capacitors. They seem ok but one or more are causing the issue...


Also i found two more things to show.


Picture 3 is the back of the small board on the back of the neck of CRT and shows signs of oxidation.
Picture 4 is at the opposite side of this small board.


Picture 5: Also the main board at the lower part of the monitor, shows oxidation on a metal, and also a strange white substance - i am not sure
what it is and if it causes issues.


Now before starting cleaning, and attempting to do things:
Picture 6: is the connection of the 'crocodile' correct in order to proceed to the discharge of the tube with the screwdriver?


Do you believe that the findings in pictures 3,4 and 5 could also cause issues?
Should i attempt to rub these with isopropyl alcohol ?











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Offline Bryce

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Re: Amstrad monitor strange behavior
« Reply #4 on: 09:57, 18 August 20 »
Hi,
So... The monitor has been somewhere damp, the oxidised jumpers etc will need to be replaced. The capacitors won't show a bulge, these are the type with a rubber seal on the bottom, the top of these don't bulge. Eitherway, they will be way out of spec and all electrolytics will need to be replaced.

That crocodile clip is connected to a piece of plastic!! How do you expect an electric charge to discharge through plastic?! It needs to be connected to the metal frame or a good earth connection.

Bryce.
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Offline Fmtrx

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Re: Amstrad monitor strange behavior
« Reply #5 on: 10:09, 18 August 20 »


I had never expected such a thing.  I thought it was a piece of metal, i did not know that it is a plastic painted in metal color  :picard:
Good thing i asked before proceeding... I will attach to the metal frame.


Ok so i will replace all electrolytic capacitors and the oxidized jumber.
Should i be worried about the white material right next to the oxidized jumber?

« Last Edit: 10:16, 18 August 20 by Fmtrx »
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Offline Bryce

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Re: Amstrad monitor strange behavior
« Reply #6 on: 10:18, 18 August 20 »
The white stuff is silastic, it's used to stop larger components from breaking their leads through vibration. It's meant to be there.

Exactly. However, as you mentioned earlier, a capacitor can be bad even without bulging. If it has dried out there is no bulge, but the value could be completely wrong, or the ESR value could be way too high.

Bryce.
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Offline Fmtrx

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Re: Amstrad monitor strange behavior
« Reply #7 on: 10:56, 18 August 20 »
It seems i have a project in my hands. The only positive thing is that the faulty component is a trivial one, and not the tube itself or other components
that are hard to find. I will also try to clean the back of the small board, and hope that no job will be needed there.

So much for the "in perfect working order" from the description of the seller.  ::)
Thank you for the directions.
« Last Edit: 16:29, 18 August 20 by Fmtrx »
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Offline Bryce

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Re: Amstrad monitor strange behavior
« Reply #8 on: 11:20, 18 August 20 »
The stuff on the back of the neck-board is from the manufacturing process, it can stay there.

Bryce.
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Offline Fmtrx

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Re: Amstrad monitor strange behavior
« Reply #9 on: 12:16, 18 August 20 »
ok! Nice, one less thing to do.
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