Overclocked MolarMac problem

[beachycove]

I have a MolarMac which came to me overclocked (via installation of a B&W ZIF G3) to 400MHz on (as I recall) an 83MHz bus. It worked fine - in fact it ran like greased lightning on 8.6 - and I have hitherto kept it thataway.

Recently, however, I get bad screen distortions every second time I start the machine, and sometimes after it has run for a few minutes. The distortion reminds me somewhat of analog board problems seen on other hardware in the past (esp. ColorSync monitors), but with a full screen still visible (with vile discoloration and with scarcely legible text) rather than a screen that is collapsing from the edges. It could be the analog board, certainly, but could it just be the overclocking putting too much stress on components?

I have not done the overclocking thing much, as I prefer my old hardware stock, but as I say, this machine came to me this way. I would appreciate the counsel of the wise, as I rather like my MolarMac and would prefer not to see it go out of service.

 

[Dog Cow]

Have you tried down-clocking it back the original speed and seeing what happens?

 

[beachycove]

No, but I will obviously give it a whirl. Knowing little-to-nothing about overclocking, my question is whether it is the bus or the processor that needs to be "underclocked" again. Would the processor speed affect the video? The bus? Or both?

Despite claims to the contrary, a MolarMac is a PITA to work on by comparison with the other Beige G3s, and I would like to keep this as simple as possible.

 

[Mike Richardson]

The 83 MHz bus is not entirely stable.

Assuming a 400 MHz G3 chip is installed then the G3 chip is not overclocked, just the bus.

Look up the jumper settings and downclock the bus to 66 MHz.

If this does not fix the problem, then you are looking at some kind of other failure.

An analog board problem will cause "natural" looking distortions, while a digital board problem will cause "artificial" or pixel-based looking distortions.

It's hard to explain. Consider a "natural" distortion to be when you put a magnet near the screen. The colors near the magnet go all wonky. You can tell it's not a "digital" or software effect.

Now replicate those wonky colors on the screen in a paint program. The effect is different.

 

[beachycove]

It is most likely the analog board/ flyback transformer/ some other mysterious item in the dark depths of the machine that is faulty, as fiddling with the jumpers as per the various overclocking instructions posted elsewhere has had no effect. It is now back at the original settings, as at least I know that they worked very well for a couple of years. The screen is getting progressively worse, with darkening, colour distortion and poor focus making it now completely illegible, all the time. The degeneration has been very rapid. I don't think this the result of overclocking, except perhaps that the overclocking may have stressed the components and brought them to a sticky end.

I read in various places of the need to renew solder joints as a cure for such problems, but am nervous of the electrical charges stored in the components. I guess it will have to go into the "to be fixed" pile. One of these days, perhaps, once I have learned properly how to discharge a CRT and know that I can work in there safely....

 

[Franklinstein]

Apple's late-model CRT-based systems seem to have numerous problems like this. I've got an original iMac with a failing flyback, and one of the original B&W G3 companion displays with bad solder joints. So, your problem is not uncommon, and it's likely that re-soldering things will get you back to normal. However, if you've never worked on the actual CRT section of a compact Mac or anything before, I can't recommend doing it yourself until you're trained properly.

Also, the overclocking thing is tricky, but not likely to cause your issue. One thing to note about the 83MHz bus is that controllers capable of running at that speed were actually installed on Rev. A G3 boards, though none were ever clocked as such. If you can verify that you've got the 83MHz part in there, then you can pretty much rule out OCing as your culprit (unless you've got the processor upclocked too much).

If you're opening it up anyways, make sure to check all of the cables, particularly those on the A/V riser card, as they may have worked themselves loose.