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 <dkel...@hotmail.com> Sent: Monday, March 21, 2022 4:50 PM To: 'General Discussion: On-Topic and Off-Topic Posts' <cctalk@classiccmp.org>; D. Resor <organlis...@sonic.net> 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. Dwight _____
From: cctalk <cctalk-boun...@classiccmp.org> on behalf of D. Resor via cctalk <cctalk@classiccmp.org> Sent: Sunday, March 20, 2022 6:53 PM To: 'General Discussion: On-Topic and Off-Topic Posts' <cctalk@classiccmp.org> 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? https://www.dropbox.com/s/f6rvemx9ldbbv5x/EPROMS1.jpg?dl=0 No need for a Dropbox account, close the login pop up and you can view the image. Thanks Don Resor
