Marconi sticking keys - UK Vintage Radio Repair and Restoration Discussion Forum

Steve Gibson · 16th Apr 2021, 12:37 am

Does anyone know how difficult it is to disassemble and clean the keys on the Marconi 2440/2442 Frequency counter?

They keypad is a bit rough and sometimes the keys don't properly engage, or they activate the key next to them. Fairly sure they just need servicing but I didn't know how serviceable those keys are.

ortek_service · 17th Apr 2021, 3:21 am

The service manual tells you how to remove the front panel assembly to get to these, and a quick Google for this finds free down downloads from KO4BB website or: https://elektrotanya.com/marconi_244...wnload.html#dl etc

The main issue seem to be that they recommend their special tool (spanner?) to undo the semi-rigid cable connection. But could probably improvise something else.

The switches on this are individual PCB-Mount fairly-standard 'D6' size ones, according to the parts list. Although just taking a look on a rather front-impacted one (where all the switches still click OK, apart from one that's stuck down) that had been chucked out, I noticed the switches have a spigot for the keycaps to go onto (rather than more common flat top ones).
It looks like Marconi have used these on many Instruments in that size case.

Contact cleaner spray may work (and also lubricate, stopping sticking), if it gets into the right parts But on the 'D6' switches, the top normally just clips, and I did recently manage to just release this and clean the badly-oxidised contacts inside one on a 40year old computer board
- Although that one wasn't sticking at all, so may need to make sure the keycaps aren't sticking on the front cover metal plate they go through, which may cause adjacent ones to activate as can't see how the matrix would be read-wrong if some aren't stuck down a bit.

Dickie · 17th Apr 2021, 8:45 am

If you can get the semi-rigid cable undone, the rest is straightforward. You might be able to get to the relevant SMA connector with a pair of long-nosed pliers, otherwise you will need to fashion a right-angled SMA spanner. You can see the problem by simply removing the rear frame and then the lower case panel.

Steve Gibson · 17th Apr 2021, 10:37 am

thanks guys

16th Apr 2021, 12:37 am	#1
Steve Gibson Triode Join Date: Mar 2014 Location: Northampton, Northamptonshire, UK Posts: 49	Marconi sticking keys Does anyone know how difficult it is to disassemble and clean the keys on the Marconi 2440/2442 Frequency counter? They keypad is a bit rough and sometimes the keys don't properly engage, or they activate the key next to them. Fairly sure they just need servicing but I didn't know how serviceable those keys are.

17th Apr 2021, 3:21 am	#2
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,440	Re: Marconi sticking keys The service manual tells you how to remove the front panel assembly to get to these, and a quick Google for this finds free down downloads from KO4BB website or: https://elektrotanya.com/marconi_244...wnload.html#dl etc The main issue seem to be that they recommend their special tool (spanner?) to undo the semi-rigid cable connection. But could probably improvise something else. The switches on this are individual PCB-Mount fairly-standard 'D6' size ones, according to the parts list. Although just taking a look on a rather front-impacted one (where all the switches still click OK, apart from one that's stuck down) that had been chucked out, I noticed the switches have a spigot for the keycaps to go onto (rather than more common flat top ones). It looks like Marconi have used these on many Instruments in that size case. Contact cleaner spray may work (and also lubricate, stopping sticking), if it gets into the right parts But on the 'D6' switches, the top normally just clips, and I did recently manage to just release this and clean the badly-oxidised contacts inside one on a 40year old computer board - Although that one wasn't sticking at all, so may need to make sure the keycaps aren't sticking on the front cover metal plate they go through, which may cause adjacent ones to activate as can't see how the matrix would be read-wrong if some aren't stuck down a bit.

17th Apr 2021, 8:45 am	#3
Dickie Octode Join Date: Sep 2004 Location: St. Albans, Hertfordshire, UK. Posts: 1,478	Re: Marconi sticking keys If you can get the semi-rigid cable undone, the rest is straightforward. You might be able to get to the relevant SMA connector with a pair of long-nosed pliers, otherwise you will need to fashion a right-angled SMA spanner. You can see the problem by simply removing the rear frame and then the lower case panel. __________________ Regards, Richard, BVWS member

17th Apr 2021, 10:37 am	#4
Steve Gibson Triode Join Date: Mar 2014 Location: Northampton, Northamptonshire, UK Posts: 49	Re: Marconi sticking keys thanks guys