[time-nuts] HP 59309A Clock runs, sets via GPIB, but no GPIB output?
francesco.messineo at gmail.com
Mon Oct 10 03:20:31 EDT 2016
I have a dump of the 1818-2295A somewhere, it should be archived in
one of my backups. I also made a replacement with a board having 2 x
28C64 SO-28 eeproms and it worked in my 59309A as far as I could test
it. However these eeproms present many glitches on the outputs during
address toggling, so it's way better to use a suitable CPLD after
recovering the equations (I'm a bit stuck on this project due to lack
If someone needs the dump, just let me know and I'll dig it out.
On Mon, Oct 10, 2016 at 5:34 AM, Paul Berger <phb.hfx at gmail.com> wrote:
> I just looked at the clock I am not using and it is 1818-2295A, it is not
> convenient for me to check the other one as it is running and in a place
> where I would have to disconnect it to get it out. I could dump this ROM
> for you but it may take me a few days as I have other things on the go right
> On 2016-10-09 10:48 PM, Bob wrote:
>> Hi Tom & Paul,
>> Some progress with the HP 59309A clock debug. Built a ROM reader
>> (Teensy++, a 28 pin WW socket, jumpers) and read out the HP 59309A U2 ROM.
>> Compared the user manual to my readings, found three stuck output bits out
>> of sixteen, and another few dozen assorted differences out of the 4096 ROM
>> Also, while moving U2 to the reader socket I noticed that the chip is
>> stamped 1818-2295A 2335 vs. the schematic which states U2 is a 1818-2193.
>> Perhaps the U2 state machine was updated?
>> The O1 (part of Next Address) bit, O9 (LOAD) bit and O11 (Rout) bit always
>> read 0. Together those stuck-at-0 bits compose the vast majority of the bit
>> differences. LOAD being always zero explains why I don't see data written
>> into the RAM when watching with a logic analyzer.
>> I'm 99% sure there is at least some bit rot, in particular there is a long
>> unused block at the end of the Talk Enable = 1 table, where all addresses
>> should match, and in the middle of that range there are just a few wrong
>> A small number of differences exist in other Next Address and Next
>> Qualifier columns, but there are only a few, not easy to tell if they are
>> just changes to the state machine or more bit rot.
>> Digging further, the serial number prefix 2510A is much newer than the
>> 1632A prefix mentioned in the manual I'm looking at, so there could be
>> differences in the schematic. Not clear if HP change pages up to 2510A
>> exist, I've not found them so far.
>> At this point, I can think of a few paths to take...
>> a) Leave it alone, still works fine as a desk clock, but useless for
>> reading TOD via HP-IB.
>> b) Build a little adapter board and replace U2 with a self-programmed 16
>> bit EPROM or a pair of 8 bit EPROMs. I could use the code in the manual,
>> buzz out the circuit to validate the schematic, and (if needed) reverse
>> engineer the state machine.
>> Tom and/or Paul, would you consider lifting the cover off your clock (just
>> 2 screws in the back) and peeking at the part number on your U2 chips?
>> That's the 28 pin ceramic ROM in the socket on the A5 board which is the one
>> at the far left looking from the front. The ROM is at the top of the board
>> and should be visible without touching anything.
>> If someone happens to have a ROM stamped 1818-2295A 2335, it would of
>> course be great to capture the bits, to remove the remaining guesswork in
>> creating a replacement image. Naturally, I checked the ROMs on Didier's
>> site, but didn't see any for the 59309A.
>> In conclusion, reading the U2 ROM shows three stuck bits, including LOAD,
>> which explains what I saw on the logic analyzer.
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