Once again, knowing no end to repairing things, I saw an HP 5316a come up on eBay for cheap ($20), that I bid on first thing, and ended up winning. Not sure I WANTED to win it, but hey, it’s a repair, I’m cool with doing those. Maybe I’ll be able to resell it, maybe not. *shrug*
3 days later, it showed up on my doorstep via FedEx, and looked to be in good condition, except the missing handle and feet, as described by the seller. Initial power up showed it power up okay, but never register any count. The gate LED would trigger, as would the sensitivity LED, and both could be adjusted. I did get a alternating flashing of the HP-IB LEDs on the front panel though (at this time, I didn’t know what this meant).
After opening the unit, I noticed two empty sockets, one on the HP-IB (GPIB) card, and one on the main board. It appeared they were used for a ribbon cable between the two, but the cable was missing. Also, another power up showed an E2 error (which translates into a failed HP-IB card)… which isn’t surprising given the connection to the HP-IB card was missing. I’m just not sure why it booted okay previous to that.
So, first thing first with all repairs of this type of equipment (especially this age), check the main filter caps. The primary 7500uF cap checked out good (though asking a meter to check a cap that large is usually a task) at 8mF (8000uF), but the two 3900uF caps both registered as about 10pF: toast. It’s fascinating the change in capacitors since this unit was made. The two 3900uF caps are both 3 legged (I guess for stability?), and all the original caps are at least 2x the volume of the new caps. During this repair, I also grabbed a handful of M-M jumper cables (like those used for breadboarding) and ran them between the main board and HPIB board. Once that was done, I powered the unit up, and it booted! At first I thought it was still broken, but if you don’t have any of the function buttons pressed, the unit just cycles all the numerical LEDs from 1-9, then repeat.
Once I confirmed the fixes worked, I ordered the ribbon cable and IDC DIP connectors online from Cables and Connectors, one of the only places that had the connectors for a reasonable price, and reasonable shipping. Obviously these types of connectors have been phased out in favor of just standard flat flex cables, or standard 1x ribbon connections.
Making the cable was pretty easy, and install was straight forward. After that, the case was closed up, and the unit works great. I’d love to make a replacement oscillator for the unit with an OXCO rather than the stock 10Mhz crystal (which isn’t temperature stabilized), but I need to figure out how much current the +5V rail can supply. Anyway, that’s for another post.
Thanks for reading!