Original/Stock Colo(u)r Classic Questions

1.1.1 — What are all these acronyms and abbreviations?

It occurred to me that we veterans use a lot of abbreviations and "insider-speak" that newbies to the Colo(u)r Classic world might not understand right away. I've provided a list of common ones here with explanations. I am not including general computer and electronic terms as it is assumed that if you know enough to be messing with upgrades, you know the basics like RAM, HD, CPU, Watt, Ohm, etc.

short for "Color Classic," "Colour Classic," or "Colo(u)r Classic," depending on how British the market was where yours was sold :)
short for "motherboard," this refers to the main circuit board of a computer containing (usually) the CPU, RAM, and external connectors (among other things). Also "MLB" (main logic board) and "LB" (logic board). Both of the latter can also be lower-case.
short for "analogue board." This is the board that the plug from the wall attaches to, and it provides power for all the components in a stock CC. Also lower-case.
short for "cathode ray tube." This is the screen that you see an image on.
Apple Desktop Bus. Uses a 4-pin Mini-DIN connector, identical in pin layout to S-video, used for connecting keyboards and mice, among other things. The CC mobo has two of these connectors; most later Macs have only one.

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1.1.2 — My CC won't start. Why not?

There are three common problems that are the source of this symptom:

The two most common are failure to turn on the power switch in the back and failure to press the power button on a known-good, connected ADB keyboard once the switch is powered on. Make sure your keyboard and cable are good, because if they aren't, it won't work. (For what it's worth, the same symptoms can occur on a 5xx-series Mac you might be considering as a parts source, so "dead" Macs often aren't.)

The third is a dead — NOT simply missing — PRAM battery. If the PRAM battery on an original CC mobo is dead, the CC will fail to output a video signal and boot up. (I got a perfectly good CC for $26 on eBay because the PRAM battery had died and the seller thought it was broken.) If you remove the dead battery, the CC will boot fine. If you replace the dead battery with a good one (this should be done), it will boot fine. If you need a PRAM battery, read this.

If the first three aren't the problem, you likely have a dead motherboard or a bad connection in your wiring harness. Double-check both and report to the Forum to await further instructions :)

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1.1.3 — Do I need to discharge the CRT before working inside my CC?

The short answer is probably not. The CC has a self-discharging circuit on the flyback transformer (the component that holds the 14 thousand volts or so that powers the CRT) that discharges the high voltage immediately when the CC is powered off. I've opened up my various CCs numerous times and have never heard even the slightest noise (indicative of a spark) when I've attempted to discharge the CRTs with a discharge tool.

Those of you who are more anal-retentive (or more worried) than myself would probably be served by discharging the CRT anyway, just to put your minds at ease. IT IS EXCLUSIVELY YOUR RESPONSIBILITY IF YOU INJURE OR KILL YOURSELF OR DAMAGE PROPERTY DUE TO UNFORESEEN CIRCUMSTANCES. YOU CANNOT SUE CHRIS LAWSON, STUART BELL, MEMBERS OF THE CCSCC, MEMBERS OF THE CC FORUM, OR THIS WEB HOST BECAUSE OF SOMETHING YOU DID. To do it, ground the blade of an insulated screwdriver, optionally in series with a 10 megaohm resistor. While the screwdriver is grounded, hold the INSULATED HANDLE and touch the tip of the blade to the anode of the CRT, underneath the red (or black) suction cup on the side of the tube.

Now, for the people who don't care or aren't worry-warts, just as long as you don't go messing with the suction cup on the CRT you'll probably be fine. As I said, the CC should discharge itself anyway.

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1.1.4 — My CC is emitting a high-pitched whine. What gives?

That sound is probably loose plates in the flyback transformer vibrating at a very high frequency. While the ideal solution would be to either replace or rebuild the flyback, there is a possible fix that Josh Shiflet passed on:

I just stuck a peice of plastic between the rectangular portion and the round portion of the flyback transformer. Evidently there is something in there that vibrates to make that noise. I did it while the CC was on so that i could tell when it was positioned properly. Just be really careful if you have it on while you do it. I used a rather long piece of plastic so that i didn't have to get very close to it. I just wanted to see if it would fix the problem and it did.

On occasion, this whine can also be caused by plates in an electrolytic capacitor vibrating at high frequency. If you can determine which capacitor it is, usually one on the analogue board, and usually a larger one, you can fix the problem by replacing the capacitor with one of identical capacitance rated for high-frequency duty.

I've had a couple people ask me if the VGA modification (or the High-Res modification) should cause these sounds to get louder or appear where they weren't present before. While I'm not totally sure on this, my gut feeling says maybe. You're increasing the horizontal scan frequency (originally 23.040 KHz, increased to 28.800 KHz with VGA mod or 32.160 KHz with High-Res mod), but all three frequencies are typically out of the range of human hearing, so this probably isn't the direct cause. My guess is that the higher voltages, particularly with the High-Res mod, cause increased stress on capacitors and the flyback transformer, which increases the likelihood of vibration in these components. Anyone with more knowledge in TV or CRT electronics is encouraged to correct me if there's a better explanation.

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1.1.5 — My screen is missing one colour. How can I fix it?

You most likely have a cold solder joint on the printed circuit board (PCB) that sits on the end of the neck of the CRT. In order to fix it, you'll need basic soldering skills and tools, so if you don't have these, find a friend who does.

Pop the back shield off of the board (it lifts right up) and inspect the board closely. If you see any solder points that are dull grey instead of silver, or are discoloured, or look physically cracked, re-solder them. To be completely thorough, you should remove the old solder, apply flux to the two areas to be joined, and apply new solder, but in most cases, you won't have to do that. In most cases, simply heating and re-melting the solder is sufficient.

If the above doesn't fix it, double-check all the connections in your wiring harness, paying particular attention to the video section. If one of those connections is intermittent or otherwise flaky, it can cause weird video issues. If nothing is wrong with the wiring harness, start checking for cold solder joints on the analogue board itself. If that doesn't yield results either, try another motherboard, or different VRAM. Bad VRAM chips or bad video circuitry on the motherboard have both been known to cause video problems as well.

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1.1.6 — My screen is all splotchy, with some dark areas and light areas and weird colours. How can I fix it?

Your CRT needs to be degaussed. Most likely, the cause of the splotchiness is a strong magnet that has come near the display. In some cases, however, the degaussing circuitry on the analogue board may have failed.

Step 1: If you know that your degaussing circuitry works, shut the CC down but leave the power switch in the back turned to the on position. If the CC is off, turn it on, but don't boot it up. Leave it plugged in and powered on like this for about 24 hours. Boot it up after 24 hours have passed and see if the splotchiness is reduced or gone. It probably will be, but if not, proceed to the next paragraph.

Step 2: If your degaussing circuitry is non-functional and you have a second CC around, simply swap analogue boards and follow the above procedure. If you don't have a second CC or the above didn't fully cure the problem, AND YOU FEEL COMFORTABLE WORKING WITH 110/220VAC ELECTRICITY, here's what to do:

Step 3: Get a strong magnet and a six-foot length of wire with a standard AC wall/mains plug on one end. Strip about 1 cm of insulation from each conductor on the other end. Unplug the degaussing coil from the analogue board and boot up the CC. Put the stripped wires into the two holes in the degaussing coil plug. With the CRT on so you can see the screen, very briefly plug the degaussing coil into the wall, taking care to remove it after a tenth of a second or so. NEVER leave this plugged in for more than 5 seconds. This should help the problem a bit, but may temporarily make it worse. After doing this step three or four times, plug the degaussing coil back into the analogue board and use the strong magnet to spot-fix any remaining areas. If you have a second CC with working circuitry, you may wish to follow Step 2 above as an additional fix. If you can't get it thoroughly degaussed, take the tube (or whole computer) to a TV repair shop and have them professionaly degauss it.

Alternative to Step 3: buy a degaussing coil on eBay for about $10-20 and use that. It's safer and less powerful than the DIY method described above. You can also use some sort of current-limiting AC transformer to step the voltage down, which is basically how the commercial coils work.

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1.1.7 — My screen is distorted somehow. How do I fix it?

Video adjustment instructions can be found in the Color Classic service manual (see below) or at Eric Neumann's High-Res modification site.

The Display Service Utility mentioned in the service manual is a piece of junk IMO; Larry Pina's excellent shareware Color Test Pattern Generator is far superior. Use it instead.

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1.1.8 — Where can I get the service manual for my CC?

Please see Section 3, "Colo(u)r Classic Technical Specs and Documentation," on the index page.

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1.1.9 — How can I start a CC with no keyboard or motherboard?

The simplest way to start a CC lacking its keyboard or motherboard is to short the +5V line in the ADB bus to ground while the power switch is turned on. To help you determine which line is the +5V in the ADB, you should consult the ADB pinout or, if you have no motherboard at all, the Takky wiring diagrams page, which is applicable to the Takky wiring harness but should assist you with a stock CC wiring harness as well.

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Last Modified on 06 November 2013
by Chris Lawson

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