Conductive paint curiosities

Hardware questions and modifications

Conductive paint curiosities

Postby DoctorOctal » Tue Jan 19, 2021 2:20 am

In Sunday night’s video meetup we discussed the conductive paint inside the PCjr’s chassis. I’ve taken photos of the paint on some of the lids I have at hand.

The first lid seems to have typical paint—fairly even, if a bit mottled:

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Lid-paint-even.jpg
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Mike mentioned the effects of heat on the paint. I hadn’t made that connection before, but the pattern is obvious now. In this example, you can see spots that were above the memory card and fan:

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Lid-paint-even-with-spots.jpg
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Here’s another lid, again with spots, but now with uneven coverage:

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This lid has spots, but the paint is very light in general except around the vent holes, the front of the disk drive, and part of the power board. Did this Jr live a hot life, or was the paint always rather light?

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Lid-paint-light-with-spots.jpg
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And then there’s this lid with distinctive charcoal gray paint. Is this the expensive silver paint used on early Jrs?

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Lid-paint-light-with-spots-reduced.jpg
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Lid-paint-uneven-with-spots-reduced.jpg
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Lid-paint-even-with-spots-reduced.jpg
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Lid-paint-even-reduced.jpg
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DoctorOctal
 
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Re: Conductive paint curiosities

Postby DoctorOctal » Tue Jan 19, 2021 2:32 am

Here’s the other side of the lid:

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Charcoal-lid-top.jpg
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Apart from the IBM sticker, notice the styling of the vent holes, which is different from that of normal PCjrs and is the same as the styling on the prototype PCjr I have (that doesn’t have any paint). Also, the lid doesn’t have an IBM badge or any adhesive residue in that spot, so I think it never had a badge.

Here are more photos of the remnants of that machine:

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Charcoal-top-with-drive.jpg
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Charcoal-front.jpg
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Charcoal-top.jpg
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Charcoal-left.jpg
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Charcoal-top-reduced.jpg
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Charcoal-front-reduced.jpg
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Charcoal-top-with-drive-reduced.jpg
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Charcoal-lid-top-reduced.jpg
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DoctorOctal
 
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Re: Conductive paint curiosities

Postby DoctorOctal » Tue Jan 19, 2021 2:42 am

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Charcoal-back.jpg
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Charcoal-right.jpg
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Charcoal-bottom.jpg
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Again like the prototype, this has a generic QumeTrak 142 diskette drive with no IBM logo and a different handle style.

The sticker on the bottom is not in the usual place; lacks the FCC, UL, and CSA certification notices; and has a low serial number with a different prefix.

The left side appears to have the circular traces of a dragon sticker. Mike explained during the call that IBM would put stickers with a cartoon dragon on machines that didn’t pass QA tests and were retained for internal IBM use only.

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I’ve seen several PCjrs with dragon stickers at Computer Reset without knowing what they were.
Attachments
Charcoal-bottom-reduced.jpg
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Charcoal-right-reduced.jpg
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Charcoal-back-reduced.jpg
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DoctorOctal
 
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Re: Conductive paint curiosities

Postby DoctorOctal » Tue Jan 19, 2021 3:26 am

Mike’s story about the early, expensive paint made with silver reminded me of this passage from Blue Magic:

Although he was not directly involved with the early development of the machine, Dan Wilkie still vividly remembers what happened when he volunteered to help solve a manufacturing problem with the Junior.

“A corporate vice president from Armonk had come down to Florida in September after stopping off at the Teledyne plant in Tennessee where the Juniors were being built. The meetings in Tennessee turned into an absolute disaster when our people found serious design problems with the machine’s engineering and the vendors’ capabilities, which meant there was no way it would be ready to announce before late fall or even by the end of the year.”



Within two days, Wilkie had assembled a team of loyalists to go with him to Teledyne to do a “quick fix.” The quick fix took three months and required direct assistance from almost 50 members of the IBM engineering and manufacturing staffs.

As Wilkie recalls, “Joe Sarubbi set up a war room in his office at Boca and he coordinated the work with me at Tennessee. We held daily meetings by phone for three months. Many of the systems had to be re-worked and re-boxed in new packages two or three times. The press was speculating that the vendors were causing the delays, but not all of the blame fell on them because we had to make hundreds of engineering changes to meet the FCC [Federal Communications Commission] Class B emissions requirements. Circuit designs and board layouts had to be redone to dampen electrical noises. This took weeks to accomplish. Meanwhile, the inside covers of the machines had to be coated with a special formula we call ‘silver paint’ that sells for $700 a gallon. The first few hundred units were painted by hand in a makeshift area and the coverage was so poor we were finishing only eight to twelve sets of covers per gallon of paint. Eventually, the painting was handled by robotizing the operations and that led to affordable yields.”

— James Chposky and Ted Leonsis, Blue Magic: The People, Power and Politics Behind the IBM Personal Computer (Facts on File Publications, 1988), pp. 153–154.
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Re: Conductive paint curiosities

Postby Gremlin5 » Tue Jan 19, 2021 9:00 pm

DoctorOctal wrote:Mike’s story about the early, expensive paint made with silver reminded me of this passage from Blue Magic:

Although he was not directly involved with the early development of the machine, Dan Wilkie still vividly remembers what happened when he volunteered to help solve a manufacturing problem with the Junior.

“A corporate vice president from Armonk had come down to Florida in September after stopping off at the Teledyne plant in Tennessee where the Juniors were being built. The meetings in Tennessee turned into an absolute disaster when our people found serious design problems with the machine’s engineering and the vendors’ capabilities, which meant there was no way it would be ready to announce before late fall or even by the end of the year.”



Within two days, Wilkie had assembled a team of loyalists to go with him to Teledyne to do a “quick fix.” The quick fix took three months and required direct assistance from almost 50 members of the IBM engineering and manufacturing staffs.

As Wilkie recalls, “Joe Sarubbi set up a war room in his office at Boca and he coordinated the work with me at Tennessee. We held daily meetings by phone for three months. Many of the systems had to be re-worked and re-boxed in new packages two or three times. The press was speculating that the vendors were causing the delays, but not all of the blame fell on them because we had to make hundreds of engineering changes to meet the FCC [Federal Communications Commission] Class B emissions requirements. Circuit designs and board layouts had to be redone to dampen electrical noises. This took weeks to accomplish. Meanwhile, the inside covers of the machines had to be coated with a special formula we call ‘silver paint’ that sells for $700 a gallon. The first few hundred units were painted by hand in a makeshift area and the coverage was so poor we were finishing only eight to twelve sets of covers per gallon of paint. Eventually, the painting was handled by robotizing the operations and that led to affordable yields.”

— James Chposky and Ted Leonsis, Blue Magic: The People, Power and Politics Behind the IBM Personal Computer (Facts on File Publications, 1988), pp. 153–154.


I worked at a place in the early 90's in Minneapolis that we cast some plastic prototype covers for Cray Computers that all had to have the insides coated with paint that had gold particles suspended in the paint itself that Cray sent over to us. I remember the boss telling us to be careful with it because it was ridiculously expensive and the were only supplying us only so much to coat each cover and we had to have a certain amount of coverage on each piece. They had it worked out that the volume they sent over should cover the surface area of the part we were making to a specific required depth of coverage.
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Re: Conductive paint curiosities

Postby Gremlin5 » Tue Jan 19, 2021 9:14 pm

Again like the prototype, this has a generic QumeTrak 142 diskette drive with no IBM logo and a different handle style.


I just saw a drive like that sell on ebay 12 days ago.... I was confused because I had never seen a qumetrak 142 with that type of handle and face plate.

Qumetrak 142 ebay
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