HP8405A Vector Voltmeter 1000MHz - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

DG7RBN_AZ · 21st Dec 2019, 12:40 pm

@ Jeremy G0HZU_JMR: I was trying to send you a private message regarding your post about the HP8405A repair, but the system does not allow me. Could you please contact me.
Thanks & 73 de Andreas DG7RBN

Station X · 21st Dec 2019, 2:18 pm

Thread reopened.

G0HZU_JMR · 22nd Dec 2019, 2:18 pm

Wow, Looking at the start of this thread I've had my HP8405A VVM for six years now...

It's still working fine although I only use it a few times a year. There have been a couple of minor niggles over the years, I do recall that the phase meter started sticking and this was because the transparent dial coating was peeling away from the backing and it jammed against the meter needle. I managed to fix this by taking the cover off both dials and sticking the coating back down. I recall having to clean a couple of the switches as well.

Hi Andreas, I can try and answer any technical questions but it's 6 years since I last looked at the inner workings of my HP8405A. So I may be a little rusty...

cmjones01 · 22nd Dec 2019, 5:19 pm

I'm also observing this thread with interest. This summer I picked up an 8405A in good condition, though inevitably missing its accessories, at a very good price from an industrial auction. I haven't tried it out yet but had a look inside and one of the boards (I don't remember which) is labelled as faulty, so there's probably some work to do.

Chris

DG7RBN_AZ · 22nd Dec 2019, 5:42 pm

Hi Jeremy,
read your interesting post about the HP VVM repair. Three weeks ago I also had one of these "good ol' boxes" on my bench for repair (from a Munich university, they use it to control a 70MHz resonator, they don't need a full blown VNA

). The -20V line was blown because of a shorted electrolytic. After complete recalibration it performs amazingly well above specs.

The job would have been much easier with your "full-size" schematics, you mentioned in the thread. Could you please send me the file because I have a second HP8405A at the attic waiting for repair. The phase meter does wild swings and it also has the "flaky meter scale" problem.

vy 73 and Merry Christmas Andreas DG7RBN

P.S. I think I've found a solution for the dissolving meter scales. I've written a Postscript program to redraw the scales and print them. A laser marking shop in a town nearby will hopefully print them on adhesive foil with a cutout for the mirror arc.

G0HZU_JMR · 22nd Dec 2019, 9:57 pm

Hi Andreas, I had a quick look and managed to find a GIF version of the big schematic. I've uploaded it here:
https://www.qsl.net/g/g0hzu//RF%20Tr...05A_bigCCT.gif

This GIF version is a bit fuzzy but hopefully it is still very useful. If you open it in explorer it is possible to zoom in closer using CTRL and the mouse wheel. I did plan to try and find a paper copy of the HP8405A manual and scan it to produce a clearer version and one that includes all of the updates relevant to my particular serial number/year. But so far no luck...

cmjones01 · 22nd Dec 2019, 10:42 pm

Quote:

Originally Posted by DG7RBN_AZ

P.S. I think I've found a solution for the dissolving meter scales. I've written a Postscript program to redraw the scales and print them. A laser marking shop in a town nearby will hopefully print them on adhesive foil with a cutout for the mirror arc.

I recently had the flaky scale problem on a 334A distortion analyzer. I fixed that by carefully removing the flaky scale, scanning it and touching it up in trusty Paint Shop Pro 7, and thresholding it so it printed well. Then I laser printed it on to self-adhesive weatherproof plastic film and applied to the meter scale plate (the old flaky stuff washes off easily with water). It works really well, but I don't know how the mirror arc would be handled.

Chris

G0HZU_JMR · 22nd Dec 2019, 11:00 pm

My repair to the dials was a bit more of a bodge. I got an old Pritt stick and made up a weak solution of 'Pritt' by adding some water to a few scrapings of Pritt. I then made a crude liquid dropper and the weight of the tiny drops of the weak Pritt solution was enough to secure the original display film back down. Otherwise, any attempt to even lightly touch the transparent peely bits of the film would result in them fragmenting to nothing. The results were very good and so far the display has not yellowed.

emeritus · 23rd Dec 2019, 1:10 am

I have a vague recollection of a mention in a 1970's HP catalogue of their meter scales being individually calibrated, but this might have been for a particular instrument rather than general practice.

loulou31 · 3rd May 2020, 2:23 pm

I am repairing a hp8405 and when I tried to adjust mechanical zero
I discovered that the amplitude meter is not a linear galvanometer….a the begining it requires250ua (-9dB) at the center 500ua (-3dB) and full range 1mA(+3dB). The scale is quite perfectly linear in dB but not exactly and it shall be possible that each was individually calibrated. The magnetic circuit has a spécial shape to bring this log response.

Regard
Jean-Louis

21st Dec 2019, 12:40 pm	#41
DG7RBN_AZ Diode Join Date: Dec 2019 Location: Ulm, Baden-Württemberg, Germany Posts: 2	Re: HP8504A Vector Voltmeter 1000MHz @ Jeremy G0HZU_JMR: I was trying to send you a private message regarding your post about the HP8405A repair, but the system does not allow me. Could you please contact me. Thanks & 73 de Andreas DG7RBN Last edited by Station X; 21st Dec 2019 at 2:18 pm. Reason: Post moved.

21st Dec 2019, 2:18 pm	#42
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: HP8405A Vector Voltmeter 1000MHz Thread reopened. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

22nd Dec 2019, 2:18 pm	#43
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: HP8405A Vector Voltmeter 1000MHz Wow, Looking at the start of this thread I've had my HP8405A VVM for six years now... It's still working fine although I only use it a few times a year. There have been a couple of minor niggles over the years, I do recall that the phase meter started sticking and this was because the transparent dial coating was peeling away from the backing and it jammed against the meter needle. I managed to fix this by taking the cover off both dials and sticking the coating back down. I recall having to clean a couple of the switches as well. Hi Andreas, I can try and answer any technical questions but it's 6 years since I last looked at the inner workings of my HP8405A. So I may be a little rusty... __________________ Regards, Jeremy G0HZU

22nd Dec 2019, 5:19 pm	#44
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,681	Re: HP8405A Vector Voltmeter 1000MHz I'm also observing this thread with interest. This summer I picked up an 8405A in good condition, though inevitably missing its accessories, at a very good price from an industrial auction. I haven't tried it out yet but had a look inside and one of the boards (I don't remember which) is labelled as faulty, so there's probably some work to do. Chris __________________ What's going on in the workshop? http://martin-jones.com/

22nd Dec 2019, 5:42 pm	#45
DG7RBN_AZ Diode Join Date: Dec 2019 Location: Ulm, Baden-Württemberg, Germany Posts: 2	Re: HP8405A Vector Voltmeter 1000MHz Hi Jeremy, read your interesting post about the HP VVM repair. Three weeks ago I also had one of these "good ol' boxes" on my bench for repair (from a Munich university, they use it to control a 70MHz resonator, they don't need a full blown VNA ). The -20V line was blown because of a shorted electrolytic. After complete recalibration it performs amazingly well above specs. The job would have been much easier with your "full-size" schematics, you mentioned in the thread. Could you please send me the file because I have a second HP8405A at the attic waiting for repair. The phase meter does wild swings and it also has the "flaky meter scale" problem. vy 73 and Merry Christmas Andreas DG7RBN P.S. I think I've found a solution for the dissolving meter scales. I've written a Postscript program to redraw the scales and print them. A laser marking shop in a town nearby will hopefully print them on adhesive foil with a cutout for the mirror arc.

22nd Dec 2019, 9:57 pm	#46
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: HP8405A Vector Voltmeter 1000MHz Hi Andreas, I had a quick look and managed to find a GIF version of the big schematic. I've uploaded it here: https://www.qsl.net/g/g0hzu//RF%20Tr...05A_bigCCT.gif This GIF version is a bit fuzzy but hopefully it is still very useful. If you open it in explorer it is possible to zoom in closer using CTRL and the mouse wheel. I did plan to try and find a paper copy of the HP8405A manual and scan it to produce a clearer version and one that includes all of the updates relevant to my particular serial number/year. But so far no luck... __________________ Regards, Jeremy G0HZU

22nd Dec 2019, 11:00 pm	#48
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: HP8405A Vector Voltmeter 1000MHz My repair to the dials was a bit more of a bodge. I got an old Pritt stick and made up a weak solution of 'Pritt' by adding some water to a few scrapings of Pritt. I then made a crude liquid dropper and the weight of the tiny drops of the weak Pritt solution was enough to secure the original display film back down. Otherwise, any attempt to even lightly touch the transparent peely bits of the film would result in them fragmenting to nothing. The results were very good and so far the display has not yellowed. __________________ Regards, Jeremy G0HZU

23rd Dec 2019, 1:10 am	#49
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,349	Re: HP8405A Vector Voltmeter 1000MHz I have a vague recollection of a mention in a 1970's HP catalogue of their meter scales being individually calibrated, but this might have been for a particular instrument rather than general practice.

3rd May 2020, 2:23 pm	#50
loulou31 Tetrode Join Date: Jan 2019 Location: Toulouse, France Posts: 65	Re: HP8405A Vector Voltmeter 1000MHz I am repairing a hp8405 and when I tried to adjust mechanical zero I discovered that the amplitude meter is not a linear galvanometer….a the begining it requires250ua (-9dB) at the center 500ua (-3dB) and full range 1mA(+3dB). The scale is quite perfectly linear in dB but not exactly and it shall be possible that each was individually calibrated. The magnetic circuit has a spécial shape to bring this log response. Regard Jean-Louis