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Flakey HP 70: post modified as RAM Chip identified.
10-22-2015, 06:22 AM (This post was last modified: 10-22-2015 07:02 AM by Geoff Quickfall.)
Post: #2
RE: Flakey HP 70
Okay, doing some research the following chips are found in the 70:

1818-0116 ROM
1818-0117 ROM
1820-0993 RAM
1820-11?9 (1169 most likely) ARC
1820-1128 clock driver reset
1818-0078 CTC

With the symptoms described above, the inability to retrieve stored numbers in either the financial registers or K and M it would look like I need to replace the RAM chip, any comments. I have a few dud 45s' which may end up being RAM chip donors to get this 70 fully operational.

Or do the symptoms suggest a defunct ROM. Again, a number stored in the financial, K and M registers are not retrievable suggesting a defective RAM. If it was the ROM, then I would be to store and retrieve numbers from the RAM.

Just checking my logic, so tomorrow I will swap the 1820-0993 with one from a dud 45 and let you know.

P.s. Thanks Eric Smith for your chip set descriptions.
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Messages In This Thread
RE: Flakey HP 70 - Geoff Quickfall - 10-22-2015 06:22 AM
RE: Flakey HP 70 - Didier Lachieze - 10-22-2015, 06:42 AM
Damn it!!! - Geoff Quickfall - 11-08-2015, 01:48 AM

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