|
Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
|
Thread Tools |
3rd May 2019, 11:22 am | #1 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
|
HP 1980's test equipment keyboard issues
I've been working on an HP3577A network analyser (bought at auction / dead display). I've now got the display back working, but the keyboard is very flaky. I wondered if anyone has experience of tackling the keyboard-switches: is it the usual contact cleaner solution or something more drastic?
John |
3rd May 2019, 1:07 pm | #2 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
|
Re: HP 1980's test equipment keyboard issues
Do you have a picture of the keyboard switches used? I have various HP ones floating around somewhere from some HP kit I trashed for the enclosure as it was BER.
|
3rd May 2019, 1:28 pm | #3 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
|
Re: HP 1980's test equipment keyboard issues
I've just this minute removed the keyboard (what a job!).
I've a horrible suspicion that these use the top-side gold tracks as part of the switch contacts? The stainless strip which is visible seems to be the spring which "snaps" and returns the key to rest position. John |
3rd May 2019, 1:31 pm | #4 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
|
Re: HP 1980's test equipment keyboard issues
They are called Bill West switches
The stainless steel snap-spring provides the action an a gold plated leaf contacts gold plated pads on the board. All assembled by heat staking David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
3rd May 2019, 2:01 pm | #5 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
|
Re: HP 1980's test equipment keyboard issues
Many thanks David.
OK: so how to clean them? "Wash" the whole board with isopropyl? John |
3rd May 2019, 2:07 pm | #6 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
|
Re: HP 1980's test equipment keyboard issues
Interesting. Not the ones I have. The ones I had were fixed on with a metal bar over the top rather than melted in situ.
|
3rd May 2019, 3:26 pm | #7 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
|
Re: HP 1980's test equipment keyboard issues
Isopropyl is probably OK.
Trike used to make them brittle David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
3rd May 2019, 4:14 pm | #8 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
|
Re: HP 1980's test equipment keyboard issues
'Back in the day' (and maybe still) HP would not supply them as spare parts. They would replace individual switches if you sent the PCB to a service centre, but they felt that most repairers could not do a proper job of the heat staking with the tools they had available.
|
3rd May 2019, 5:11 pm | #9 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
|
Re: HP 1980's test equipment keyboard issues
Oddly, I did quite a few on instruments I was working on, on my bench without any special tools other than a turned-down weller soldering iron bit. The trick was to just turn the iron on for long enough to get the right temperature. The right temperature being found by melting a bit of the old switch. Being in an HP plant, we had raw switch parts in stores.
I suspect the problem these days is the gold's worn through. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
3rd May 2019, 8:18 pm | #10 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
|
Re: HP 1980's test equipment keyboard issues
I took the bull by the proverbial horns and flooded the switches/board with neat Isopropyl (over a large bowl), whilst giving each switch a good bit of exercise. Then blew out the excess alcohol with compressed air and gave it a second do. After drying and putting everything back together it seems to have done the trick: pretty much perfect responses from the keys.
Now to try to sort out why the log sweep has an abrupt 7dB amplitude step as it passes thro 100kHz (not present with a linear sweep: is there a change in RBW filter around 100kHz??) This one could run & run! John PS I suspect this instrument spent a couple of decades in a lab together with smokers... |
3rd May 2019, 9:12 pm | #11 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
|
Re: HP 1980's test equipment keyboard issues
Probably RBW switching. You should see a step in the noise floor, but the scaling of normal signals should be right at all frequencies. The apparent level of noise-like is dependent on the bandwidth being simultaneously detected.
David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |