This weekend was busy ... Been sitting on some stuff for a while and this was the ideal day to crack them open.
A dead 53181. Does not power on. Turns out some of the big ceramic power resistors in the supply had 'desoldered' themselves over time. These machines do not have a real power-off switch. the main supply is always running to keep the oven hot. This particular machine had its oven removed before they tossed it. So i switched it back to its internal TCXO ( it has a smaller TCXO on the main board. installing the oven disables that one and switches the signal over. I have an oven in my older frequency counter so i will transplant it ( HP only has one model oven so they are compatible. just a matter of making an adapter cable )
The power supply. a custom module built by delta electronics. The power resistor just above the transformer had desoldered itself.
THe base board. a motorla 68331 32 bit microcontroller does the heavy lifting. the empty footprint abvove is for a floating point coprocessor but they never used this. THe service manual for these machines deals with the 53181 53182 and one other model. for each variation the FPU is crossed out. i guess they figured they had enough kick to run the floating point through a library
the little board bottom right is the boostconverter for the frontpanel VFD
the Xilinx3042 gate array contains the counter logic. the empty footprint can hold an identical 3042 used in the 53182 version of this machine.
Parts left of the xilinx are all ECL 10F series gates and comparators. input ranging relays do the rest.
The frontpanel
First boot : Success !
Working
THe 3Ghz options is a simple MMIC based amplifier followed by a fujitsi divide by 64 chip. i got the schematics and board layout. going to make this thing myself