Color Classic losing focus over time.

[12bit]

Hi Board.

I have a Color Classic that recently started to behave weird.

When I boot the unit sometimes a weird sound occours (kind of like a fizzling sound) lasting a couple of seconds before the 'mouse hand/cursor' comes up.

But that's not all. The focus on the monitor is kind of looping.

I mean; it starts off with some kind of focus getting worse during a minute or two - and then it is sharp as it should be - slowly loosing it again over a couple of minutes and so on and so on.

Any advice on what to do would be MOST helpful!!

Thanks !

Kenneth

 

[Paralel]

An analog board issue would be my best guess.

 

[Mac128]

You're going to need to check your voltages first. Definitely don't use it until you confirm the power distribution. Once you have done that, if the behavior continues, you are most definitely facing repairs on the analogue board involving a soldering iron (not sure of your level of proficiency). These are symptoms of failing PSU components, for which there is no simple fix. At best you are only buying yourself some additional time, but repairs will definitely be needed eventually.

 

[tomlee59]

A fizzling sound, plus erratic focus usually points to a high-voltage problem. It could be as simple as crud on the crt pins or socket/board, or as serious as a breakdown inside the flyback transformer. As a first diagnostic step, you'll need to open it up and take a careful look around. Report back on what you find, and we can go from there.

 

[techknight]

ive seen focus/g2 blocks inside the flyback fail. and cause driftness in focus/brightness of CRT. they are pots and pots wear out. Eventually depending on the design of the flyback, ive seen focus/G2 short straight to the HV would result in a loud SNAP and then dead. shorted HOT instant.

 

[Paralel]

What's a "G2 Block"? I'm not familiar with that term.

 

[12bit]

Hi guys.

Thank you very much for all your feedback - here is some more detailed info.

I opened 'her' up and apparently everything seems fine.

The problem occured after I exchanged the internal HDD with a new one. Before that the monitor somewhat 'drifted', but after the HDD change it now just has this 'in and out of focus' behaviour.

I have somewhat given up and has decided to set up either my old Classic or my IIci. I would like to get her up and running again though - so any thoughts or recommendations will be highly appreciated.

Kenneth

12bit.com

 

[Paralel]

Everything seems fine as in your broke out your multimeter and checked all the components on the analog board or everything seems fine as in you took the cover off, didn't see any fire, black smoke, or large sparks shooting out of somewhere and then put the cover back on?

 

[12bit]

The last 'Everything Seems Fine' example

No - So far I haven't measured anything. I will if I know what to look for - sadly I don't.

I am not a total newb when it comes to electronics (and multimeters for that matter), but I really have no clue as to what to look for.

I guess a Service Manual will be the next thing to look for

Thanks again;

Kenneth

12bit.com

 

[Mac128]

Many of the same basic principles apply.

http://68kmla.org/files/

 

[techknight]

the focus/g2 block is the technical term of the screen/focus controls that are part of the flyback, and in some instances are NOT.... but the color classic flyback, the focus/g2 block is integrated into it, and it can fail. Also if your HV starts going low, your focus and screen will drift as well, but the raster will also loose brightness, and start to "bloom" but the HV cannot go too far out of spec, as the X-ray protection circuitry will engage and shut down the deflection circuits. I know some of these terms as I am in the TV repair business. The G2 voltage is your screen voltage. the "screen" control is the voltage that goes into the G2 connection of the CRT.