HP 8161A Repair - Page 1
Forum section: electronics / testgear

author: fisafisa
author_rank: Regular Contributor
timestamp: January 06, 2021, 01:06:25 pm
content: HiI just bought a 8161A as a repair project.From the pictures it looks complete even if some cables are not connected.Anybody with a copy of the service manual?

author: fisafisa
author_rank: Regular Contributor
timestamp: February 06, 2021, 12:42:32 pm
content: A couple of month ago I got hold of a broken 8161A.It is a pulse generator with the ability to select the pulse amplitude up to 5V and with a bias up to -5V.The service manual is not available of internet but upon inspection it was clear that a good deal of the components werefrom the 8060A for which you can find the manual.The output card, which was specific to this model, instead had a daughter module from the HP8082A another pulse generator.At the end I was able to find two versions of 8160A service manuals and the service manual for the 8082A.Combining the informations from the 3 I was able to understand and fix most issues.The first problem was the Power Supply.It is a switching unit, and most of the output capacitors had developed a leak.A similar repair job can be found inhttps://www.eevblog.com/forum/repair/what_s-this-part/msg958219/#msg958219but in my case all these wet-foil tantalum capacitors had burst open and spread the acid corroding their leads and some of the golden traces.I replaced them with SMD capacitors mounted on small pcbs.RIFA capacitors were still ok, but I replaced them all, just in case.Since the unit came with a broken fuse I tested the PS gradually feeding in a current controlled 120V DC (having disconnected the AC fansthat were not spinning and getting hot) using my bench PS 4 outputs in series.That worked fine, no smoke and all voltages in spec!But the fan are needed as some big power resistors were getting hot.Next repair was the linear regulator boardMore of these tantalum capacitors had died, and one in particular destroyed a bunch of traces.In addition a driver transistor was a bit loose as one his legs had been severed.to be continued...

author: fisafisa
author_rank: Regular Contributor
timestamp: February 23, 2021, 04:43:35 pm
content: After replacement of the bursted capacitors on the PS i got rid also of the RIFA capacitors that were visibly cracked.The big switching power supply module is now working and now the attentions turns towards the linear regulator board.In this board the same type of capacitors have burst open too and leaked the acid on the traces and in some areas completly wiped out the gold covered copper.After a bit of investigation I was able to understand how the traces were connected and they were replaced using rigid copper wire.A transistor needed replacing too as somehow one of its pins were snapped at the baseTesting the PS on the bench using 3 HP bench power supplies to recreate the various unregulated lines turned out to be quite tricky, but at the end I was convinced that everything was ok and I tried it together with the switching PS.All is well!Next time I am going to repair the PCU board and the motherboard. After that I should be able to see the instrument come to life!