Hewlett Packard 5300B Measuring System

 

Repairing and clean-up of a Hewlett Packard (HP)5300B Measuring System with a 5305B 1,300 MHz Counter module.

This was sup­posed to be just a clean-up project, but this one turned into a bit more work that I had expected.

This HP 5300B sys­tem was pur­chased on Ebay as “pow­ers on, the num­bers dis­play on the screen”. When it arrived I plugged it into my Watts Up? pow­er mon­i­tor and turned it on. Nothing hap­pened, there was no dis­play and the pow­er mon­i­tor showed .000 amps.
The sell­er did make it right by refund­ing part of the pur­chase, so now it was a chal­lenge to see if I could get this unit work­ing again.

To start with the fuse­hold­er cap was not the orig­i­nal and was inter­mit­tent­ly mak­ing con­nec­tion. After replac­ing the cap, I had AC line volt­age to the trans­former and low volt­age AC to the board. I noticed on fur­ther inspec­tion that the trans­former alu­minum sup­port was severe­ly deformed, which was also caus­ing bend­ing of the cir­cuit board and an attached pow­er tran­sis­tor using the alu­minum frame as a heatsink.

After a hour of dis­as­sem­bly, straight­en­ing, and reassem­bly it was time to try pow­er­ing up the unit again.
Still no dis­play or DC sys­tem voltages.
After a bit more trou­bleshoot­ing the prob­lem end­ed up being a dam­aged con­tact on the 50 pin Centronics style con­nec­tor that mates to the dif­fer­ent plug-on mod­ules for the sys­tem. Pin 25 DC +22 volt pow­er is con­nect­ed via the plug-on mod­ule to pin 50 (DC-IN) which then is switched by the front pan­el pow­er switch, and then is con­vert­ed to sys­tem volt­ages. This allows the sys­tem to uti­lize a bat­tery pack between the plug-on mod­ules for portable operation.
Most like­ly the dam­age hap­pened at the same time the alu­minum frame was deformed by a severe drop caus­ing the trans­former to move things around inside the case. This was not caused by the most recent ship­ping to my loca­tion, as I also found three of the four plas­tic board mount­ing latch­es dam­aged with miss­ing latch­es, but no remains of the latch­es inside the case when opened.

Now that the unit was work­ing, it was time to per­form a through clean­ing and take some pho­tos of the 5305B 1,300 MHz Counter plug-on module.

The Hewlett Packard 5305B is a beau­ti­ful exam­ple of qual­i­ty engi­neer­ing from the mid 70’s by the design team at HP. This unit was built in late 1981.

I still need to check the cal­i­bra­tion of the 10.000 MHz oscil­la­tor, but cur­rent­ly do not have any­thing accu­rate enough to do the job.

Hmmm, sounds like anoth­er future project!