ID UV erasable PROMS used on an IBM PC board?

dwight dkelvey at
Tue Mar 22 13:14:48 CDT 2022

It is true that the glass blocks most of the UVC from florescent lamps. The key word here is "most". It is not a 100% block.
When looking at aged data in EPROMs one should error on the side of caution.
As an example, I have a pole lamp that I use a standard florescent bulb, with the typical spiral of 3 turns. I used it for about 4 hours a day for about a month when I bumped into the lamp shade.
It crumbled into pieces. At the base where the lamp shade was protected from direct light of the lamp, the plastic seemed to be of full strength, even though the temperature was higher at the base.
I don't know the intensity of the various levels of UV at different frequencies leaking from the lamp. I do know that it takes a specific high frequency of UV in the UVC range as a minimum to erase EPROMs. This plastic may be sensitive to UV closer to the visible spectrum.
I'm only saying that one should use a lamp that has zero UVC as apposed to a lamp that has a filter reduced level of UVC.
Years ago, I won a bet by allowing an EPROM to sit exposed for 3 months in an industrial setting, using florescent tube lighting. It did not erase any of the data in that condition. I suspect it had some effect but unlikely much more than that lost by cosmic rays over the same period of time.
Holding an aged EPROM about 2 inches from a florescent lamp is still not something that I'd bet on.

From: D. Resor <organlists1 at>
Sent: Tuesday, March 22, 2022 2:40 AM
To: 'dwight' <dkelvey at>; 'General Discussion: On-Topic and Off-Topic Posts' <cctalk at>
Subject: RE: ID UV erasable PROMS used on an IBM PC board?

There are a few other problems.

The power supply does not power up.  Three of it’s four voltages are missing (+5vdc, +8.5vdc, +13vdc).  With no connections to the power supply board, the +5vdc measures 4.92vdc while the other two voltages are still zero volts.

The second issue I found upon removing the driver and processor board is moisture had entered the typewriter’s electronics and the connector between the two boards has corrosion on many of the pins and on the PWB near the connector.

I do not have access to a microscope.

I know it has been explained to me elsewhere that UV exposure from florescent lamps can erase the proms.  The way I understand is the glass of the florescent lamp filters out any UV radiation (as does the piece of glass mounted in front of quartz halogen lighting).  In order that a UV lamp can operate correctly the tube must be made of quartz, not glass.

Am I wrong here?

Don Resor

From: dwight <dkelvey at>
Sent: Monday, March 21, 2022 4:50 PM
To: 'General Discussion: On-Topic and Off-Topic Posts' <cctalk at>; D. Resor <organlists1 at>
Subject: Re: ID UV erasable PROMS used on an IBM PC board?

The dies look to have consistent wire bonding. That would mean they are one of the standard EPROMs made by Intel, just preprogrammed by Intel before shipping. The numbers wouldn't be intel numbers they would be IBMs inventory numbers. My guess is that they are 2732s. You might use a microscope and look at the edges of the dies. They often have the die type in the metal layers around the edge some place. Avoid using florescent ring lights as a large amount of UVC leaks from these. White LED are or incandescent lights.

Also power it up and note which pins look to have signals. if any of the lines have what looks like a constant voltage measure it to the nearest .01 volts if you can. That will help determine if it is driven by a signal or a hard tied wire. Lower left and upper right should be ground and power pins.



From: cctalk <cctalk-bounces at> on behalf of D. Resor via cctalk <cctalk at>
Sent: Sunday, March 20, 2022 6:53 PM
To: 'General Discussion: On-Topic and Off-Topic Posts' <cctalk at>
Subject: ID UV erasable PROMS used on an IBM PC board?

I cannot find a datasheet by any of the numbers silkscreened on these ICs.

Could these be proprietary IBM P/N numbers?

No need for a Dropbox account, close the login pop up and you can view the


Don Resor

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