Mac Plus ozone?

Curtis H. Wilbar Jr. rescue at
Sun Apr 13 08:32:36 CDT 2008

John Robertson wrote:
> Curtis H. Wilbar Jr. wrote:
>> I was given a Mac Plus a while back... and never tested it....
>> Decided to give it a quick test...
>> Other than needing a boot floppy which I'll have to dig up.... it 
>> powers on, video
>> looks good, monitor is stable and all...
>> But there is a faint sound (think of it as a cross between crickets 
>> chirping and clicks)
>> and after a while, it smells to me a bit like ozone at the top of the 
>> Mac.
>> I'm thinking maybe high voltage leakage ?
>> Anyone have any experiences with these old Macs that can point me at 
>> what to look
>> for ?
>> It might well be OK as it is... but I don't want to risk damage 
>> occuring as other
>> than a few dings and scrapes and a bit of yellowing, it is in 
>> remarkable condition.
>> -- Curt
> Ozone smell is just the high voltage at work. A slight leakage that 
> may indicate moisture or excessive dust on the monitor where the HV 
> lead clips to the side of the picture tube. You might be able to 
> reduce the smell by opening the case and (after waiting 24 hours to 
> discharge) clean the glass around the HV Anode clip (may have a rubber 
> disc protecting the clip) with a red (usually red) fat insulated wire 
> coming out of the picture tube cone. There is a special coating on the 
> tube that starts about 2 inches away from the anode clip and coats the 
> glass cone - do not remove or damage this if possible. It is 1/2 of 
> the capacitor element of the picture tube Lyden jar type capacitor.
Called DAG I believe.

I'll have to open this up, probably check it out in a dark room, then I 
can always
discharge with my hv meter or wait patiently for at least a day (and 
then double
check with the hv meter :-) ).

> Alternatively the flyback could be damp or filthy with dust. This is 
> found at the other end of the fat wire (normally red) leading from the 
> cone of the picture tube. You can wipe it with a damp cloth, taking 
> particular care not to rotate or move it relative to the frame - as 
> this will break wires and cause it to fail. Most flybacks are solid 
> enough that this is not a concern but in my early B&W video game 
> monitors the flyback coil was not well secured and subject to failure 
> from being turned or twisted whilst cleanig or just day to day 
> bouncing around...
which B&W video games ?  Vectors or Rasters ?  I have an Asteroids I haven't
repaired yet.  (I have around 12 vids, aprox half rasters, half 
vectors)  I am the
'repair shop' for them (but sadly get very little time, so several or 
awaiting repair).

Currently (off topic, but possibly of interest to some) on the repair 
room floor:
Star Wars (mathbox probs), Rip Off (sound problems), Tempest (flakes out 
large vectors and crashes randomly, might be bad ram socket from a ram 
replaced), Major Havoc (mainboard problems, to be built into a Tempest 
cab), Xevious
(the dreaded Matsushita monitor is slewing video at the edge of the 
(rotated) screen),
and I'm sure I'm forgetting a couple.

My Joust leaks HV... I think the DAG coating has become damaged (flaked 
off, or
partially 'cleaned' off by someone).  Especially if there is moisture in 
the air, it
crackles, and IIRC I observed a faint lighting show around the DAG 
coating.  I
believe you can get a coating to redo the DAG, but I haven't researched 
that far yet.

OK.. enough off topic (hrm... maybe not too of topic.. they are 
essentially computers :-) ).

-- Curt

> John :-#)#

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