HP8640B: A9 assembly - UK Vintage Radio Repair and Restoration Discussion Forum

Nymrod121 · 5th Nov 2015, 10:41 am

Morning,

Being a glutton for punishment I've acquired a second HP8640B. This one is Options 1,2&3 and has the later type of 'range vs deviation' switching/interlocking differential assembly (the infamous 'A9' unit).

I've spent a few hours on temporary fixes re. gears and am up against a reassembly conundrum ...

Is there anybody with a similar unit who would be able to take & provide pictures as follows:

Orientation of the two ribbon cables and associated header connectors (where these are plugged into the metering motherboard, I've noticed that the headers on mine have one corner mitred, similar to certain types of IC sockets. The headers are fully populated with 2x8 pins and unfortunately there is no corresponding 'index' on the motherboard, so the order of the ribbon colour coding is the only way to correctly orient for re-assembly);

Relative alignment of the plastic wheels and contacts (after the assembly has been removed with range and deviation controls set fully CCW, as spec'd in the manual)

Any/all help would be much appreciated, thank you

Best wishes

Guy

Julesomega · 6th Nov 2015, 1:47 pm

What exact detail do you need? This is 8640 is Option 1, 2

Nymrod121 · 6th Nov 2015, 10:08 pm

Thanks for your reply

Yes, that's the type of assembly I've been looking at over the last few days.

I've got the ribbon cable connector positioning sorted (many thanks Richard - trh01uk - for your help on that one).

It's the relative alignment of each contact disk that I need to be sure of - ideally, close-ups of each once the range and deviation controls have both been set fully counter-clockwise.

I shot myself in the foot on this by having not set both fully CCW prior to removal. This was simply because I couldn't get my hex. key into the control knob setscrews without risking damage to the front panel. With hindsight (20:20 vision), I should have fitted a couple of simple control knobs immediately afterwards so as to get both sets fully CCW before proceeding with removal of the entire A9 assembly...

Hope this clarifies!

Best wishes
Guy

Julesomega · 6th Nov 2015, 11:13 pm

Range .5 - 1MHz, dev. 5kHz has the rows of wipers vertical:
on the dev'n sw they are uppermost (with the instrument the right way up)
on the front range sw ditto
rear range sw wipers are downwards (as per photo)

hth

Nymrod121 · 7th Nov 2015, 2:06 am

Bingo! - the disc at the back was about 30° off vertical ...
Tomorrow I'll reinstall and test.
Many, many thanks for your help

Best wishes
Guy

5th Nov 2015, 10:41 am	#1
Nymrod121 Nonode Join Date: Apr 2012 Location: Worcestershire, UK. Posts: 2,052	HP8640B: A9 assembly Morning, Being a glutton for punishment I've acquired a second HP8640B. This one is Options 1,2&3 and has the later type of 'range vs deviation' switching/interlocking differential assembly (the infamous 'A9' unit). I've spent a few hours on temporary fixes re. gears and am up against a reassembly conundrum ... Is there anybody with a similar unit who would be able to take & provide pictures as follows: Orientation of the two ribbon cables and associated header connectors (where these are plugged into the metering motherboard, I've noticed that the headers on mine have one corner mitred, similar to certain types of IC sockets. The headers are fully populated with 2x8 pins and unfortunately there is no corresponding 'index' on the motherboard, so the order of the ribbon colour coding is the only way to correctly orient for re-assembly); Relative alignment of the plastic wheels and contacts (after the assembly has been removed with range and deviation controls set fully CCW, as spec'd in the manual) Any/all help would be much appreciated, thank you Best wishes Guy Attached Thumbnails __________________ "What a depressingly stupid machine." [Marvin: HHGTTG] Last edited by Nymrod121; 5th Nov 2015 at 10:53 am. Reason: corrected typos

6th Nov 2015, 1:47 pm	#2
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,117	Re: HP8640B: A9 assembly What exact detail do you need? This is 8640 is Option 1, 2 Attached Thumbnails

6th Nov 2015, 10:08 pm	#3
Nymrod121 Nonode Join Date: Apr 2012 Location: Worcestershire, UK. Posts: 2,052	Re: HP8640B: A9 assembly Thanks for your reply Yes, that's the type of assembly I've been looking at over the last few days. I've got the ribbon cable connector positioning sorted (many thanks Richard - trh01uk - for your help on that one). It's the relative alignment of each contact disk that I need to be sure of - ideally, close-ups of each once the range and deviation controls have both been set fully counter-clockwise. I shot myself in the foot on this by having not set both fully CCW prior to removal. This was simply because I couldn't get my hex. key into the control knob setscrews without risking damage to the front panel. With hindsight (20:20 vision), I should have fitted a couple of simple control knobs immediately afterwards so as to get both sets fully CCW before proceeding with removal of the entire A9 assembly... Hope this clarifies! Best wishes Guy __________________ "What a depressingly stupid machine." [Marvin: HHGTTG]

6th Nov 2015, 11:13 pm	#4
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,117	Re: HP8640B: A9 assembly Range .5 - 1MHz, dev. 5kHz has the rows of wipers vertical: on the dev'n sw they are uppermost (with the instrument the right way up) on the front range sw ditto rear range sw wipers are downwards (as per photo) hth Attached Thumbnails

7th Nov 2015, 2:06 am	#5
Nymrod121 Nonode Join Date: Apr 2012 Location: Worcestershire, UK. Posts: 2,052	Re: HP8640B: A9 assembly Bingo! - the disc at the back was about 30° off vertical ... Tomorrow I'll reinstall and test. Many, many thanks for your help Best wishes Guy __________________ "What a depressingly stupid machine." [Marvin: HHGTTG]