Symptom on Classic II: Screen Wobble When Accessing HD?

[Paralel]

I have a Classic II that needs to be recapped. I have noticed during times of heavy HD access that the edges of the screen will visibly wobble. Is this a caps issue, or does it sound like the problem extends to the analog board or some other major internal component? When there isn't heavy HD access going on the screen is perfectly stable.

 

[nvdeynde]

The Classic I/II Analog boards are notorious for bad capacitors. Even though they are the last model of the B&W compact macs, the capacitors are of poor quality. They were cheaper than the SE series for a reason I suppose.

Anyway you should be able to test this quite easily. Monitor the +5 and +12v lines idle and then during HDD activity. They will probably already be at the low side and when the hard drive is reading/writing it will get lower because the capacitors are bad.

 

[Paralel]

Does anyone have a link to the tech specs for the original drive that was in the Classic II?

I'm wondering if the larger drive in it, which was there when I bought it, might be pulling too much from the analog circuitry. If so, I might want to downsize to the proper drive type to reduce some of the strain on the system.

It currently has a Fireball 540S (Apple ROM) in it.

 

[nvdeynde]

The original HDD for a Classic II is a 40MB or 80MB drive from IBM/Connor/Quantum.

 

[techknight]

I recommend using an analog meter when watching for voltage spikes and sags, peaks can surpass the sample rate of a DMM and make it hard to see unless the rails are grossly sagging.

using an analog meter you can catch the peaks/sags easier. IMHO.

 

[Paralel]

I actually came across a really old post somewhere that described this particular problem. They suggested it was due to a physically larger replacement HD extending into the case, and being so close to the monitor, that when the HD is active, it interferes with the proper operation of the monitor (I'm guessing as a result of magnetic interference with regard to the deflection coils?). Does this make any sense?

 

[krye]

Hum...magnetic interference from a hard drive? Wouldn't that be worse for the hard drive as opposed to the monitor? If there was some sort of interference, you'd think the hard drive would throw read/write errors like crazy.

 

[uniserver]

Pretty much I had the same problem with my classic I.

The caps go bad reducing the amount of power available.

Its not because of any magnetic interface.

The issue with running on bad caps like that, it will progressively get worse as the caps totally die.