Hello to all...and happy new year
(that was what we already said in 2020
).
I did buy on an auction website a HP 5334A counter.
Unfortunately when i arrived, there was display on the front panel. I could hear the buzz of the transformer.
Openning of the box, test of the voltages on the test points. Everything was OK
After multiple power on/off I noticed that there some display for "fraction" of a second during the power on... that kept
my spirit for trying on.
After getting an online copy if the service manual of HP 5334B ( a sibling), and some study... I noticed
- display is controlled through an 8 line I/O Port bus from the main cpu...
- With the scope and checking some of the direct lines (STR1 & STR2) from the EXEC CPU to the from panel board that this CPU was OK. (of use here, we can put the unit in diag mode by pressing the reset button while powering up the unit. In this mode the unit keeps doing some diag tests going on step to another and cycling when pressing the reset button).
Unfortunately, some of the Data lines to the 7 segment drivers kept high impedance state.
Checking what other component was on the lines I found that this IO Ports of the EXEC CPU was also shared with the GPIB uC.
Removing this last CPU from its socket and starting the unit solved the display problem of the unit.
I have now an error 9.2 (GPIB CPU problem) when I power on the unit and after validating the error the units goes to "counting"...
Still trying to solve the GPIB CPU problem, how can I check if the problem is the CPU or some other component.
Note : 4MHz clock and reset lines is common to both EXEC CPU and GPIB CPU. This CPU is MOSTEK MK3870/42... this is
a Factory MASK programmed CPU with fw MK16255N-15. There seems some way to read the code using the test pin of the CPU and doing a "serial dump"...and after that to program a MK38P70 chip with some external UV-PROM.. But this version of the CPU cost "an arm"...
Should I try to mount the CPU on a breadboard and do some testing ?
Thanks in advance for any hint
Olivier