Wavetek Model 171 Function gen - Page 1
Forum section: electronics / testgear

author: wolfalex
author_rank: Regular Contributor
timestamp: December 29, 2015, 08:30:26 pm
content: Hello,Today I tried my old WaveTek Model 171 function generator/Synthesizer after 2 years of storage in a cellar, and a move to my new apartment, and the duty cycle of the output signals wascompletely wrong. First I thought probably a power regulator inside the unit failed again as it happend once in the past, but after double checking all the supply rails I saw that the were allok.After knocking around a little on the top board I found the problem: microchip IC5 seems to have a bad contact in its socket. Probably corrosion. IC5 forms the positive and negative currentsource which then is used for signal generation inside the unit by charging and decharging on capacitor. After knocking on IC5 the duty cycle of all the signals was perfect again.My function gen and "repair" is probably not the most exciting thing, but I thought I add some pictures here, in case somebody is interested in it. The generator comes with a nice digital"frequency" dial in function which is used here.

author: wolfalex
author_rank: Regular Contributor
timestamp: December 29, 2015, 08:31:44 pm
content: Some more pictures.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: December 29, 2015, 09:23:01 pm
content: Yep. Beating on stuff is usually the first repair method I try. Next is to remove socketed components or boards one at a time, look at them carefully on both sides, and plug them back in. You'd be surprised at how many PCs and other equipment I've fixed using these two secret techniques.

author: wolfalex
author_rank: Regular Contributor
timestamp: December 31, 2015, 10:46:22 am
content: First I was afraid that the problem will be hard to find, but at the end I was very happy. I never expected that by simply bumping on the PCB that I will find the problem within 5 minutesNow I only have to find out if the problem is a solder joint, the IC socket itself or corrosion on the part.

author: wolfalex
author_rank: Regular Contributor
timestamp: December 31, 2015, 11:17:47 am
content: Reseating the part did it. No problems anymore.

author: dom0
author_rank: Super Contributor
timestamp: December 31, 2015, 11:30:22 am
content: If it sits in one of these stupid TI-style sockets (grabbing the pins by their sides instead of their faces, see image below, easily recognizable how the contacts in the sockets are different) the issue is likely to come back. Long term solution: replace socket.(Image courtesy of Jimnarem by TekWiki)

author: wolfalex
author_rank: Regular Contributor
timestamp: December 31, 2015, 11:55:15 am
content: Hello, thank you very much for the info. Yes, unfortunetly the part sits in one of these sockets. I have never seen them before and I was already wondering about them (especially about the top plastic half of the socket which seems to be loose and can be moved a little bit with the hand).I think you are right, most likely the fix is not good enough. I am only afraid that changing the socket could be a major effort. I think I will need to take out all the control rods, unscrew the voltage regulators from the backplate and so on.Have you done this fix before?

author: dom0
author_rank: Super Contributor
timestamp: December 31, 2015, 12:23:02 pm
content: Yes, they are common in older Tek gear. No need to replace them if the pins of the IC are gold plated (like most Tek ASICs are), but for normal ICs I just replace them "on sight".But I see your troubles here, no access to the solder side of the board and taking it apart looks like it's not just a matter of unplugging a few connectors. Maybe try putting something like Deoxit into the socket and flush with IPA?

author: wolfalex
author_rank: Regular Contributor
timestamp: December 31, 2015, 02:27:09 pm
content: I think right now I will keep it like it is. Especially because I spend quite some time bumping on the IC and the PCB around the socket and nothing bad was happening anymore. If it breaks again I know now what to do