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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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21st Aug 2019, 6:44 pm | #1 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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HP 8558/8559 Switch Issues
This is not a new topic to the forum. There are previous posts about how to repair these switches.
Today I have been looking at my own 8559 Spectrum Analyser which used to work OK, albeit with a few issues with the Ref Level / Attenuator switches. Recently it has refused to sweep which is not helpful with an SA. I have removed the plug in from the Display Unit - HP182T. In the bottom was a tell tale 4 contact piece of spring fingering and when I looked harder there was another sandwiched in a chassis overlap. Inside the plug in itself I found two more so I have 4 identical so far - but where did they come from? I have a pdf of the manual - it is not brilliant - but so far as I can see. Ref Level Switch should have 2x 4 contact pieces and they are still there - I assume this is OK then. Freq Span/Div Switch (Front) and Resolution BW Switch (Rear) have no contacts at all that I can see. There are pimples where the contacts originally fitted by something akin to a plastic rivet. We will come back to this. Time / Division Switch should have 2x 4 contact pieces - these are hidden from view for now so unknown until unit is dismantled further. Trigger Switch appears to use 2x 4 contact pieces - these both seem to be missing and pimples are visible as above. My question here is how are the switches which are shown in the circuit schematics as needing 6, 8 and 10 contacts (Freq Span) realised? Should I be looking for other finger combs with more contacts? I don't seem to have enough to go around as it is! The Freq Span/Div switch does not look wide enough to accommodate 10 contacts. The space available on that rotor (with the hairpin spring) looks like it takes 4+4 like the others. Was some trick done to mingle the pads and get more switch work out of fewer physical contact fingers? |
21st Aug 2019, 7:22 pm | #2 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
|
Re: HP 8558/8559 Switch Issues
Here is the schematic for the switch, which apparently needs 10 contact fingers.
It seems pretty sure, by looking at the PCB itself, that there is a thicker middle ring which is probably a +15V circle. That leaves 3 rings outside and another 3 inside for contacts which must produce the correct output code if using 2x 4 finger contact combs on the rotor. Could a cunning PCB layout produce the right output codes? There is no PCB layout diagram given unfortunately. Last edited by Jon_G4MDC; 21st Aug 2019 at 7:30 pm. |
22nd Aug 2019, 2:14 pm | #3 |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,706
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Re: HP 8558/8559 Switch Issues
I don't have any of the 180 series SA plug-ins, but the they all seem to shed those contacts from the switch rotors as you already know.
The 8557A has them too, I don't know if they are exactly the same as the 8559 but there are some pictures of the front switch rotors showing the contacts in this repair thread; https://www.vintage-radio.net/forum/...ad.php?t=80757 I also found a picture showing the PCB track layout behind one of the rotary switches in a 8558B plug-in, it also looks to have another PCB behind the first one with more rotary switches. It's from this webpage with quite a detailed repair write-up & lots of pictures; https://lazyelectrons.wordpress.com/...180d-hp-8558b/ Hopefully some of this will help with your repair. David |
22nd Aug 2019, 2:42 pm | #4 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
|
Re: HP 8558/8559 Switch Issues
Thanks David, that appears to be track work for one of the other switches but the site does provide proof positive that the Freq Span/Div switch has 2x 4 contact fingers.
When I get it apart I will take my own photo of the PCB. I don't like the homemade spring contacts - I think his PCB might have a short life. I hope to find a source of the right fingerstock (optimist!). Anyway now I can count up how many contacts I am missing. At least it seems all are identical. Jon |