[time-nuts] HP 59309A Clock runs, sets via GPIB, but no GPIB output?

Paul Berger phb.hfx at gmail.com
Thu Oct 6 22:08:05 EDT 2016

On 2016-10-06 4:56 PM, Bob wrote:
> I'd like to ask the HP 59309A owners on time-nuts if the following symptoms sound familiar, and if so, what would the fix be?
> o New-to-me HP 59309A clock.
> o Late build, 1985 date code on many parts.
> o I replaced the big 1900 uF electrolytic before plugging it in.
> o Visual inspection very clean, no corrosion, no battery.
> o 12v reads 13.1v, 5v reads 5.3v, -2v reads -2.9v.
> o Front panel switches and buttons all work as expected.
> o Internal and external osc. both work as expected.
> o Internal "format" switch set to 0000 i.e. comma, cal, no space.
> o GPIB works to *set* the time, using Prologix Ethernet adapter.
> o Prologix Ethernet adapter attached directly to the clock, no cables.
> o Python code to set via GPIB attached below.
> o Setting time via GPIB always works, tried many times.
> o Reading time has never worked.  All I get is lots of ASCII 44444444444444444444444...
> o Reading with Prologix ++read command
> o Switches set to 1100010 i.e. Listen, ADDR 2 for normal operation
> o Tried switches as 0000010 i.e. Talk Only, also resulted in continuous 4444444444444444444...
> o Tried very long delays between every GPIB command, no change.
> o Tried removing top cover and running a fan to bring entire clock to 21C, no change.
> o Tried gently reseating the four boards and three socketed PROMS, no change.
> Thanks to TVB for hp59309.c sample Windows Prologix USB code.  I based the Python Ethernet code on TVB, to read from the clock he sends command C and then ++read.  When I do that all I get are a zillion 0x34 '4' characters.
> Seems strange that all the GPIB commands work.  I tried R reset, P pause T resume D day H hour M minute S second manually and they all work just fine.  I have never been able to read anything reasonable though.
> As to the Prologix Ethernet adapter, I believe it is working OK electrically as I have been using it for weeks at a time reading PPS time intervals from a trusty HP 5334B counter, the adapter has read hundreds of thousands times from the 5334B.
> Is there a trick to using the Prologix to read from the 59309A?
> I did notice that the 59309A has at least one trick - in TVB's code where he reads the Prologix settings and only writes them if they need to be changed, that is actually required(!).  Just writing them every time seems to put the adapter into a strange state.
> Page 4-2 of the 59309A manual seems to imply that the "Output State Machine" generates the GPIB output messages, using input from the "Data Memory".  AFAICT, those two functional blocks are the only ones that are not working for me.
> I think A4U18 ROM is OK as it handles GPIB command decoding and R P T D H M S commands all work.
> A5U15 appears to do the ASCII encoding for SP, CR, LF, ", : so it may or may not be OK.
> A5U2 is described as "STATE MACHINE ROM (A5U2). This 4K ROM controls the operation of the circuits that develop the talk output of the 59309A."  Has anyone experienced failure of this ROM, and do the symptoms match what I'm seeing?
> This is a lovely clock, and while I can't actually think of a reason to *need* the GPIB time output, I'd still like to fix it.
> Cheers,
> Bob Marinelli
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I have two of these clock both working, however I have never tried to 
read one with anything like a Prologix adapter I have only used mine 
with HP computer of a similar vintage, however as long as the adapter 
adheres to the handshake timing it should be ok.  I was going to say 
that the -2 seemed excessively high, but I just checked one of mine and 
it is -3V and works fine.  Since it display fine my guess would be that 
the problem area would be at the right end of sheet  2 of the A5 board.  
Yes it is possible for ROMs to go bad, but I have not experienced it 
personally.   Since your adapter is reading something that would suggest 
it is handshaking on the GPIB bus, but the fact that it seems to run 
away might suggest that the send sequence does not terminate correctly, 
in the mode you say you have it set for it should send a string of 18 
characters including the terminating CR LF and then stop, however in 
talk only mode there will likely not be a big break between strings.

  If you set it to talk always you should see the RAM addresses cycling 
and on the input side it should alternate between addresses coming from 
the A4 side and addresses coming from the state machine ROM.  If you had 
a logic analyzer you could monitor the inputs and outputs of the RAM as 
well as the addresses as it cycles through loading and reading out the 
addresses.  On page  5-9 there is a table of the state machine ROM 
contents note addresses are in octal, you could remove U1 and U3 and 
then supply your own TTL level addresses to the ROM to see if you get 
the correct bits out or it A7 is controlled by the rear panel talk 
always switch.  You could also remove the ROM and read it out 
externally, but be very careful handling it, they are not kidding when 
they say they are very static sensitive, I would recommend a properly 
grounded static mat and wrist strap.  Out of circuit you will need to 
create your own rig to read it since it requires multiple voltages.

If it was me I would dive in with a logic analyzer, there are flow 
charts to tell you how the sequence of events should go and the analyzer 
will quickly tell you if that is what is happening.


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