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NCR System 3330 Dallas RTC Mod

The Dallas DS12887 RTC inside my NCR System 3330 PC had died a long time ago. Unfortunately, this made the machine unbootable from the hard drive, since it would forget the hard drive settings on each restart. Instead of finding a replacement, like for the Commodore PC 30-III, I opted for the external battery modification instead. I got this working with just two regular AA 1.5V alkaline batteries, a huge success!

The initial error on every startup was as follows:

NCR Battery Power Lost

Fortunately, the Dallas RTC is a in a socket on this machine, easily extracted:

NCR Dallas RTC Extracted

To perform the mod, two sections of the case needs to be opened, which I did with a Dremel tool:

NCR Dallas RTC Dremeled

Afterwards, it's possible to solder on leads for a new battery:

NCR Dallas RTC with new battery leads

I installed a new 2xAA battery holder inside the case, connected to the RTC:

NCR Dallas RTC external battery

The machine is now working again, settings can be saved to CMOS and booting from hard drive is possible:

NCR Powered On

Topic: Repair, by Kjetil @ 14/03-2020, Article Link

Commodore PC 30-III Repair

The Commodore PC 30-III is a AT-class 286 clone PC running at 12MHz with 1MB of RAM. My first and initial problem was the battery failure upon booting:

Commodore PC 30-III Battery Failure

For some reason, It was not possible to get past this error and continue booting anyway, so a replacement was needed. I got hold of a Glitch Works GW-12887-1 which can replace the original Dallas 1287 RTC in this machine:

Commodore PC 30-III Dallas DS1287 RTC

This is unfortunately soldered directly to the motherboard. But I cut a socket and soldered that one on instead:

Commodore PC 30-III U201 Socket Replacement

In which the replacement fits nicely:

Commodore PC 30-III GW-12887-1

This got the machine booting properly. But after a while of playing around with Compact Flash disk replacements, magic smoke suddenly appeared. Which became my second problem. I located the source; a burned ceramic capacitor:

Commodore PC 30-III Burned Ceramic Capacitor

From what I could find out online, these capacitors can fail if cracks appear in them, and moisture gets in over time. So that's most likely what happened to this 30 year old component. I got a replacement and removed the bad one, which disintegrated almost by itself:

Commodore PC 30-III Capacitor Replacement

The brand new ceramic capacitor in place:

Commodore PC 30-III New Capacitor

The machine is now up and running again:

Commodore PC 30-III Front

Topic: Repair, by Kjetil @ 08/12-2019, Article Link

Commodore 1541-II Floppy Drive Repair

I was able to repair my Commodore 1541-II floppy drive, which is typically used together with the Commodore 64.

The first problem was that I do not have the original (external) power supply, but fortunately it uses fairly standard +5V and +12V voltages, which are also used by most PC hardware. So I made an adapter from a 4-pin molex to a 4-pin DIN connector:

Commodore 1541-II Power Adapter

The pinout of the DIN connector can be found here among other places.

When powering up the drive for the first time, it would keep the drive motor running constantly, which is apparently a known problem. Some other people online said this could be caused by a faulty PSU or bad ROM chip...

When I attempted to continue troubleshooting the next day, the situation had worsened. Now the power LED on the drive would flash a little on power on and slowly fade away. Symptoms of a short circuit or something perhaps...

With no idea on what to do about this, I decided to try to replace the electrolytic capacitors, which people often do on restoration/repair projects.

There are only three of them on the main board, all 10uF and 25V, located here:

Commodore 1541-II Capacitor Locations

Old and new replacements:

Commodore 1541-II Capacitor Replacement

To my surprise, this actually worked, and the drive is now working:

Commodore 1541-II Working

I have a theory: Two of those capacitors I changed are between the incoming 12V/5V and ground, acting as "decouping/bypass" to filter out noise. If there happened to be a short circuit or weakened resistance in the capacitors, that would explain parts of the symptoms at least.

Topic: Repair, by Kjetil @ 26/10-2019, Article Link

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