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CRT Monitor Issue (Advice/Recommendation Sought)

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n45048:
Hi everyone,

I thought I'd reach out to the EEVblog community for some assistance.

I'm in the process of expanding my vintage computer collection and managed to score a bunch of old Apple Macintosh hardware for $10. Absolute gold! Part of my acquisition were two Apple 'Multiple Scan 720' 17" CRT monitors. But both have identical problems.

Whilst my expertise lies in IT/Data forensics, I'm not a CRT/Television/Power Supply expert. I'll try to explain the symptoms as best as I can:

Both power up and display a signal without any problems. Overall, the picture is pretty good; Sharp, good colour, good shape, no burn-in.

ISSUE #1:The maximum brightness/contrast settings seem a bit low. I mean the image is fine, but I feel that I shouldn't have to crank the settings all the way up to achieve a normal picture.

ISSUE #2: Perhaps the more serious issue. Intermittently, the monitor has a "glitch". The image will distort for a fraction of a second and an audible "click" or "tick" can be heard. My guess is that there is an issue with the power supply.

Could anyone with some CRT expertise point me in the right direction? I'm even happy to pay someone to diagnose/fix my problem (I live in Sydney). Poking around CRT picture tubes has always made me nervous so I'm hesitant on working on it myself.

Michael.

Monkeh:
#2 sounds like it's degaussing. Have you not had a CRT before? :P

justanothercanuck:
The brightness issue is probably capacitors.

As for the clicking noise, if it is indeed the degaussing coil, that shouldn't happen during normal operation.  It should only degauss when the monitor is initially powered up.  That might also be a capacitor issue, but don't hold me to that one.  ;)

n45048:

--- Quote from: Monkeh on February 21, 2014, 07:29:47 am ---#2 sounds like it's degaussing. Have you not had a CRT before? :P

--- End quote ---
It's definitely not degaussing. It degausses for a few seconds on power-up, which is expected. Even the manual degauss function works as expected. The behaviour I'm describing is abnormal. I'll try to capture it on video and upload.

G7PSK:
It could well be just dirt build up on the outside of the crt. leaking off the ht. with the odd arc over. Try cleaning the crt's first by blowing or vacuuming  the dust of and then clean any residual grease ect off with alcohol swabs. I have often found that is all that is required, especially if the monitors or TV's have been used by smokers or in a kitchen or workshop environment. That is where I would start, but remember to turn off and unplug the monitors some hours before opening them up preferably the day before to let the tube charge leak off.

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