[ale] OT: Question regarding whining monitors (for you EEs out there)

[Scott Castaline]

Geoffrey wrote:

> John Wells wrote:
>
>> Guys,
>>
>> I have an Apple eMac that has monitor issues (see older threads in 
>> which I've mentioned it).  Most of the the time everything works 
>> fine, but if I leave it on for 15+ minutes or so on average, the 
>> monitor begins to emit a high-pitched whine that seems to grow in 
>> intensity over time...to the point that I'd rather jab an ice pick 
>> into my temple than to sit at it for very long.
>
>
> I'm not an EE, (changed to CS after two semesters..) but as I recall, 
> this is likely a transformer and also a possible indicator of 
> shortened life.
>
>> I'm preparing to take it to the only authorized support center here 
>> in Greensboro...CompUSA, but want to be fully wearing my BS armor 
>> before going in.  In my experience, these guys will throw out any 
>> random explanation, assuming you're a DAU who doesn't know better.
>
>
> I wouldn't take anything to CompUSA, for repairs, but I understand 
> your issue if that's all you've got to work with.  These days, not 
> many folks repair monitors, and I doubt CompUSA will have anyone on 
> hand to give you a reasonable solution (outside of replacement).  Most 
> of these type of folks know little (if anything) about electronics.  
> Then know how to swap cards out, install software and the like.
>
Usually that's an indicator that there is a problem in the high voltage 
section (flyback xfrmr is part of the HV). Sometimes just adjusting the 
variable inductors that control the oscillators in the HV (these control 
the scan rates) can eliminate the problem and extend the use of the 
monitor. To replace the HV section is the second most expensive part in 
a monitor with the CRT being first in cost to repair. It's been a while 
since I've worked on monitors ( about 15 years ago ), so this advise may 
not apply to the newer monitors. If you attempt to do this yourself bear 
in mind that you are poking around in 32Kv +, especially when you get 
near the anode cap on the tube. that will be the thicker gauged wire 
that connects to the bell of the CRT, DO NOT TOUCH THAT, IT WILL 
DEFINITELY BITE YOU!!! You use to able to get alignment tools that are 
essentially plastic version of screw drivers and hex drivers. The 
inductors will be tubular with thin wire wrapped around it and a hollow 
iron core inside. It is this core that you adjust with a hex driver. 
There are also parts that look like mini metal disks with a slot in them 
or a cross. These are potentiometers (Pots) or variable resistors. Use a 
small plastic screw driver either phillips(for the cross) or flat 
tip(for the ones with slots). The circuit board is usually silkscreened 
identifying major parts. Look for inductors labeled as HV, Horiz. Freq., 
or Vert. Freq. same for any pots. Also keep in mind that the tube 
behaves like a giant capacitor and even with the monitor powered off and 
unplugged, the still holds a charge that will definitely bite. I suggest 
that if you do attempt this youself. do it one handed, using your right 
hand and if you have to sit on your left hand. This will prevent 
shocking youself through the heart. It is not a pleasant feeling. I've 
had that happen to me while working on a portable heart monitor, the 
circuit boards formed a box around the tube and were not labled. I 
grabbed the unit and discharged the tube through my chest. Fortunatelly 
it was a low powred tube and was monochrome so it only had approx. 5 - 
15 KV. I mean to and don't mean to scare you, just be carefull.