Fluke 6160A (Frequency Synth) - is this normal behaviour? - Page 1
Forum section: electronics / repair

author: cprobertson1
author_rank: Frequent Contributor
timestamp: January 29, 2018, 01:29:46 pm
content: Good afternoon to you all!I have a Fluke 6160A Frequency Synthesizer here, 1973 vintage, that I've half-repaired.-PSU - blown - replaced-Smoothing caps (x3) - physical damage - replacedAnd now, we have power and we're up and running... mostly.I don't seem to be able to find a manual for this - and the onlyspec-sheetI've seen indicates that it is a 4-30MHz unit.What I'm curious about is why this seems to be able to go lower than this - if I set it below 4 MHz - it adds 2.5 MHz on - meaning if I set it to "0 Mhz" - it displays 2.5 - and anything I dial in gets "added" onto that +2.5MHz offset - until I get to 4 MHz, at which point the offset vanishes, and it continues normally up to 30MHz (and it seems to be remarkably in-spec - it's certainly within the tolerance of my frequency counter!)Is that lower-than-spec'd frequency to be expected? THe unit has been repaired in the past - and I suspect that a module from a different unit has been added - but I can't find any information to say which modulesshouldbe present! Some are clearly marked with "6160A" - but others just have a series of numbers (all on little brass badges, incidentally! Very pretty!)I don't suppose anybody might be able to find a manual for this? I've only been able to find manuals for the B-model so far (and they wanted £40 for it - I'm notthatdesperate)Many thanks in anticipation - and sorry in advance if this is a dunning-kruger-esque matter - I'm afraid I don't generally work with the insides of test-gear (I try to keep them closed if I can - don't want all those pesky electrons to escape!)

author: cprobertson1
author_rank: Frequent Contributor
timestamp: January 30, 2018, 10:25:16 am
content: Figured it out last night - looks like the output divider module was taken from the 6160B model; though it isn't marked as such, it has a number of extra rows populated for the higher frequency ranges (even though they aren't used).That might explain the lower-than-spec'd available frequency - but then again, it might have been able to do that anyway!The next question is: rust - what is the best way to repair rusty component leads? While I'd like to just replace all the ICs - there's a number that aren't manufactured anymore, and don't seem to have adequate replacements.Got a series of DIP packages on the "frequency control computer" board (mostly 7400-series logic) that are a but rusty: many I can replace, but some are a bit old-school and some I can't even find datasheets on!Is there any particular way I should go about trying to clean these up? I can (carefully) remove some of the corrosion and then plate the lead in solder - but I'm worried about accidentally destroying the lead in the process!Interesting to note is that we actually have a number of different types of corrosion on the board: which my awesome NDT workmate has confirmed with an x-ray PMI gun- Black rust (low oxygen/low moisture) resulting in Iron(II)Oxide (Fe3O4) - in this particular case, most likely galvanic corrosion occurring underneath an intact conformal coating that is restricting oxygen availability. It forms a thin but stable coating that spreads slowly- Brown rust (high oxygen/low moisture) resulting in Iron(III)Oxide (Fe2O3) - most likely the component was not conformally coated, or the coating has failed, allowing for atmospheric exposure. Interestingly, it seems to be a group of Motorola MC4001 ICs that have the worst example of this type of rust.- Nickel Oxide (NiO) - green corrosion, nickel leaching out of the alloy and corroding on the surface - different colour (lighter) than copper corrosion (and confirmed acuprous) - only found on two ceramic DIP packages - suggesting they must have used a high nickel alloy for their pins (I don't know why that would be!)- Cuprous Oxide (Copper(II)Oxide(Cu2O)) - formed on the coils of the transformer on the original power supply - insulation had failed in multiple places - probably one of the reasons the PSU was dead. I'm unsure how it came to be in such bad shape unless the waxcloth coating used to separate the primaries and secondaries was corrosive. There are also traces of this on the outer casing - suggesting it is brass coated.These two aren't actually a type of corrosion - but they're still deterioration of the base metal- Zinc Pest (allotrope of Zn) - seen on exactly one RF can - which crumbled to bits but is otherwise alright- Tin Pest ( allotrope of Sn) - possible tin disease on the exposed, tin-plated motherboard. Patches of crusty, frangible dark grey material which scrapes off. Touching it with the soldering for a few moments makes it look shiny again. Unsure how to test if it is in fact tin pest - or if it's just corroded tin (which, however, I was under the impression is white in colour)Anyhoo - thought you might find the various spectrum of corrosion on this unit of interestI'll grab some high-res pictures of it later on this week to let you have a gander!That's the interesting thing about inorganic chemistry. I was trained in organic chemistry - where pretty much everything you deal with is a colourless liquid... though I once had a slightly yellow liquid this one time. Organic chemistry on the other hand - oh! It's magical! So many colours!