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I have a Commodore 128D that hasn't been powered in about 15 years. I want to begin using it again. It has been stored in cool dry places like attached garages, in a cardboard box.

I hope this question can apply to the general case of anybody who acquires an old computer and wants to use it without damage.

My particular concerns are bad capacitors or other power supply problems, mechanical problems with disk drives for example, and other problems or stupid mistakes I'm not aware of.

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There are several simple precautions that are always worth taking when powering up a vintage microcomputer after long periods of storage or non-use. The minimum, simple steps, should include:

  1. Place the computer on an electrically safe workbench, preferably one that includes a grounding strap for the user. A wooden table is an OK substitute, just avoid static discharge from your body.
  2. Open the computer for visual inspection. Dust inside the case and around any ventilation ports (i.e. PSU fan) should be blown out using compressed air. Grime can be removed using isopropyl alcohol (70%) and a clean rag.
  3. Look carefully at the component side of the motherboard and any cards for anything abnormal. Common anomalies to check for are leaky electrolytic capacitors, damaged or improperly inserted chips, empty sockets (missing chip?), and any evidence of component overheating, like blackened, charred area around a resistor or cap, or on the PCB.
  4. After properly sorting out any of the above, if needed, you should gently press on each socketed component to ensure it is completely and correctly seated in the socket.
  5. Assuming it can be done without exposing you to dangerous voltages, disconnect the internal PSU from the motherboard, then power on the PSU only from AC power. Watch and listen carefully for any arcing or sparking so you can power it right back down quickly. If it looks OK, then wait several seconds and check for any unusual or acrid odors from the PSU. If it appears stable, you should check the PSU voltages with a multi-meter next. Obviously, checking voltages will require you to obtain some basic troubleshooting guide so you know which pins to check and the specified voltage you should see. See answers to this question.
  6. If above is good, reconnect PSU. Remove any peripheral cards that are not essential to subsequent testing, then power up the main board and CPU. Again, watch and listen carefully and check for odors or other anomalies so you can power it right back down.
  7. Ensure any fans that are installed are working and that the system or PSU is getting adequate airflow.
  8. If good so far, you can power back down, re-assemble the case, and start testing the machine with video displays and other peripherals.

This might sound like a lot of steps, but barring necessary repairs along the way, it can be done in 5 to 10 minutes.

You mentioned the floppy drive in the Commodore 128D as well. All the same simple checks above for the main board should be done for the floppy drive motherboard too. Frequently, the read/write head on a floppy drive will need to be cleaned before it can access disks. This is done by wetting a cotton swap with isopropyl alcohol and using that to gently clean the delicate head area. Also, if you keep the Commodore case open during operation, you can visually observe if the head is moving laterally across the disk. Sometimes it can get stuck or sort of sputter if the track it moves on needs lubricating after a long storage. I normally use a small amount of silicone lube for the metal tracks, and you should attempt to remove any old lubricant before applying the new. Of course, there can be many other failure modes for floppy drives, but these two simple things have gotten many drives working again for me. On 3.5" drives, the moving parts associated with inserting and ejecting the diskette are also prone to needing old lubricant cleaned off and new lubricant applied.

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    Err... I mean "Place the computer...". Thx. – Brian H May 6 '17 at 3:56
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    Agree in principle, but: Some old computers, especially those that have known problems with brittling keyboard membranes and connector stripes, are better left untouched and closed - Any movement of those connector stripes might break them and replacements might be hard to find. Others, like the ZX Spectrum, that is known to self-destruct in certain conditions, I'd open in any case. If you open the computer, you need to be prepared to replace those membranes. – tofro May 6 '17 at 8:01
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    Running some 80s era switching power supplies without a load connected can stress or even wreck them. Even more commonly, they will give erratic output voltages that have no relation to what they will output in loaded state. – rackandboneman May 6 '17 at 16:43
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    Great answer - suggest adding "allow device to warm up to room temperature overnight if its been stored in the cold" higher up, and about number 2 "visually inspect for anything that shouldn't be inside the device, including dead animals or nests. Doubly careful if you're in Australia." – Criggie May 6 '17 at 21:12
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    I would add "search the internet for common problems found when powering up the system". Some systems, most notably (IMHO) the BBC Micro, are notorious for almost all exhibiting the same problem when powered back up - in the case of the BBC Micro, one of the filter capacitors in the power supply vents in a rather impressive and bad-smelling display. This usually doesn't cause any lasting damage to the BBC Micro and in fact it can usually still be used in the meantime until you replace the capacitor, but it's feasible other computers might have similar issues that cause damage. – Muzer May 8 '17 at 9:25
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My advice for the first start:

  • Let the computer slowly warm up to room temperature.
  • Perform a careful "audio test" - I mean tilt the case or slightly shake and hear. If some strange noise appears, it would be better to open it and find a part making the noise. It could be a piece of plastic or something torn off - a wire or some other part.
  • Check all connectors with the metal pins. Is there any sign of rust? If so, better open the case (rust will be probably inside too) and clean it carefully.
  • Once you have opened the case: check any strange things, e.g. stains of some liquids, dust or inflated capacitors.
  • Smell it. Do you detect some "burned electrical circuit" scent?
  • As someone already mentioned: Some of the old computers, like Spectrums, have parts which can degrade, e.g. the membranes, etc. Be ready to replace them. Membranes have often microscopic cracks...
  • Do not open the case if not necessary.
  • Last but not least: be ready to turn it off as soon as you smell something strange. :)
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    I'd strongly suggest opening the case and doing a visual inspection before doing the "audio" test... What if the power supply isn't seated properly, and shaking it causes it to crack the mainboard? It'll save a couple of steps in your list, as well, and if someone is worried about whether there was storage damage, then opening the case is necessary. – Ghedipunk Dec 10 '19 at 15:44
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There can be no one size fits all recommendation for all vintage computers.

For example some DEC power supplies incorporate an over voltage circuit that short-circuited the output of the power supply. If you attempted to apply power with the power supply disconnected from the computer this circuit would trigger. If you made major changes to the internal power supply load in the full sized boxes by removing all the memory and i/O cards in one change you could trigger this circuit. Taking the cards out in stages and adjusting the power supply voltage avoided this problem. The thinking behind this design was a replacement, modular power supply was only worth a small fraction of the total system cost. An over voltage power supply could instantly do tens of thousands of dollars worth of damage in a minicomputer.

As well as looking for signs of leaking electrolytic capacitors, look for capacitors that have changed shape e.g. tops that have slightly bulge up. For an old system performing a visual inspection, assuming all is good then taking the final step of applying full mains power is asking for a loud bang, possibly with a small puff of smoke, the failure of the system to start, with smell of an electrolytic capacitor that has expired, a distinctive smell.

There is a piece of equipment called a variac which allows you to control the mains voltage applied to a system. I would use a variac to very gradually increase the mains voltage while monitoring capacitor and power supply voltages. Depending on the circuits and physical layout this has the potential to deliver a fatal shock. What you are attempting is to reform the electrolytic capacitors. There is a high probability of very old components changing value. Due to manufacturing tolerances electrolytic capacitors tended to be sold with very wide tolerances compare to other components. Good designers assumed the worst and tended to specify electrolytic capacitors rated with a higher capacitance than absolutely necessary for good circuit behaviour. This means you have a reasonable chance of success. A good precaution is to use a Cathode Ray Oscilloscope (CRO) or modern equivalent to check power supply ripple. A Digital Multimeter (DMM) could also be used. Very old circuits may be specified for analog multimeters with an Ohms per volt (Ω/V) and using the wrong meter could give erroneous readings. The problem with a CRO is you may not know what is acceptable ripple and what is unacceptable.

There are two types of integrated sockets used in vintage equipment and the more expensive machined pin type should be more reliable. The type using spring metal contacts can have reliability issues. Soldered joints should be more reliable. Check for hairline cracks on the Printed Circuit Boards (PCB) copper tracks. Dry or bad solder joints can cause problems and may be found during a close visual inspection. Search the internet for any active user groups and investigate known issues. Visual display units contain even more hazards due to the Extra High Tension (EHT) voltage supply and the dangers associated with a Cathode Ray Tube (CRT).

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  • I'm familiar with the variac approach for re-forming caps on old audio equipment, but wouldn't it be risky to ramp up supply voltage on an old digital system? I don't think the 5V supply, even if analog instead of switching, would behave very nicely, and the TTL it feeds could be even more problematic. – jeffB Dec 10 '19 at 19:40
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Commodore 128D has an internal PSU so you don't have the risk to have a faulty external PSU, typical for older C64 and C128. Se this other answer: What is the proper way to test the PSU output for a Commodore 128D?

Commodore motherboard doesn't have an RTC battery and doesn't use tantalum capacitors so you don't have some problems that plaugue Amiga and IBM PCs and compatibles of that era.

To add to the answer of PDP11 if you don't have a variac you could rig an incandescent bulb in series of the mains and put a 60W bulb. I f the bulb does not lights up there aren't shorts in the transformer. Do it with the PSU disconnected from the mainboard, because the C128 has a switching 5V regulator that should shut down on undervoltage.

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