UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 1st Nov 2021, 7:23 pm   #1
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default AVO test leads - bad connections to meter sockets

I recently picked up an Avo 8 MK5 at a sale with a load of other stuff and it's the first time I've found one with what look like nearly new (condition) test leads. It's also proved after testing, to be the only Avo I've got that seems to work on all its ranges - must get round to fixing the other meters sometime! After cleaning the contacts for the late 90s Varta D cell that was still installed and replacing the 2 amp fuse which fell apart when removed to clean its contacts, the low ohms range worked well, but not with the genuine test leads being used. The high ohms range worked once the 15 volt battery had been re-stuffed with Poundland button cells!

These Avo leads are absolutely useless. The connection to the socket terminals is too lose to be reliable, particularly the positive one on this meter. I usually use ordinary 4mm plug leads or spade connections when using Avos, but thought that I might try using these proper leads if I could get them to make a reliable connection to the meter socket terminals. I thought about folding the shield back and cutting a slot in the 'solid' brass pin and splaying it out a bit, but that would really be butchery. Before I investigate further, does anyone have a method they've used to make these connections with original leads better? Can the terminal sockets be adjusted in some way, or is it best to just keep the original leads as 'artefacts' and carry on using basic leads as I've always done?
Attached Thumbnails
Click image for larger version

Name:	P1140741.jpg
Views:	119
Size:	127.6 KB
ID:	244789   Click image for larger version

Name:	P1140742.jpg
Views:	147
Size:	71.0 KB
ID:	244790  
Techman is offline  
Old 1st Nov 2021, 7:30 pm   #2
Craig Sawyers
Dekatron
 
Craig Sawyers's Avatar
 
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,941
Default Re: AVO test leads - bad connections to meter sockets

Oddly I haven't had too much of a problem with AVO leads. But like all meter leads like those the connections have to be clean. Application of metal polish, the clean that off, then IPA, then contact cleaner.

FWIW I have the same parlarver with Fluke leads on DVM's on ohms range.

Craig
__________________
Doomed for a certain term to walk the night
Craig Sawyers is online now  
Old 1st Nov 2021, 7:35 pm   #3
The Philpott
Dekatron
 
The Philpott's Avatar
 
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,081
Default Re: AVO test leads - bad connections to meter sockets

-I've noticed there is a lot of variance with the test leads and their various terminations & accessories. The socket in the other end has an inconsistent size on some, to the extent that a Holdtite Croc. sometimes either won't go in, or is hopelessly loose. I have done some mixing and matching to cobble together satisfactory sets!

Most if not all of my 'shrouded, rapid type' leads like the one you've pictured- have split pins at the 'meter' end- and this can be persuaded apart with a blade if it ever seems loose. I wonder if it's significant that all of my meters are of an older model than yours..

Is there a way of knurling the loose pin by some means i wonder. I think cutting a slot in it has a poor chance of success

Dave
The Philpott is offline  
Old 1st Nov 2021, 8:05 pm   #4
pmmunro
Octode
 
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,797
Default Re: AVO test leads - bad connections to meter sockets

All the "genuine" Avo leads of this type which I have seen have had biforcated pins and I have had occassion to open out the slot a little. A solid pin is never going to be satisfactory; there has to be some resiliance to make a reliable contact.

The user manuals insist that genuine leads should be used and that these have a resistance of 0.02 ohms per pair but I can't see the logic of this, other than to ensure sales. (The standard of insulation is another matter). On current ranges, the leads are external to the shunt arrangement so should not affect the accuracy. On voltage ranges the leads have a negligible resistance compared to the multipliers and on resistance ranges there are too many other variables for the leads to make any difference, especially as the zero setting is adjusted before use.

Much longer leads, about 1 metres each, were listed and I have seen these in use. As they were very similar to the standard ones in every other respect, I can only assume that they had a higher resistance.

The earlier rubber insulated leads were prone to fracture of the wire near the ends and the insulation could perish with more extreme age. The later plastic insulated leads seem to be more robust.

The price of the genuine leads was also always a deterrent so I would favour making up your own leads using suitably rated 4mm plugs and sockets and extra flexible test lead wire with an approproste voltage rating.

PMM
pmmunro is offline  
Old 1st Nov 2021, 9:39 pm   #5
TowerRadio
Hexode
 
Join Date: Mar 2008
Location: Bristol, UK.
Posts: 388
Default Re: AVO test leads - bad connections to meter sockets

You can clean the orifice with contact cleaner on a Q tip,then slightly widen the gap in the plug.Les
TowerRadio is offline  
Old 1st Nov 2021, 11:02 pm   #6
Alistair D
Nonode
 
Alistair D's Avatar
 
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
Default Re: AVO test leads - bad connections to meter sockets

In my case I used IPA on the Q tip. The amount of dirt that came out of the sockets on every one of my meters was amazing.

I would suggest that this is a task worth doing every once in a while.

Al
__________________
I won't tell you how I discovered that.
Alistair D is offline  
Old 1st Nov 2021, 11:22 pm   #7
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: AVO test leads - bad connections to meter sockets

Thanks everyone. Yes, I think cleaning is definitely needed. Anyway, after wondering if I'd actually got a pair of 'fake' leads, I put on my best reading glasses and under a strong light with a good magnifying glass and a bit of scratching, I can see that there actually is in fact a completely closed up slot - my face was as red as the colour of that rubber insulation! I tried to open it up with the smallest jewellers screwdriver, but risked busting it and the same with a scalpel blade, so I'm going to take them out into the workshop and clamp them securely and tap a sharp blade into the slot to open it up. I honestly thought these plugs were solid. If you got a wander plug and left it clamped up for 4 decades, it's guaranteed to still spring open to some degree on release, but not these leads - you wouldn't believe that the slot would close up so completely as to not be visible!
Attached Thumbnails
Click image for larger version

Name:	P1140758.jpg
Views:	103
Size:	63.5 KB
ID:	244809  
Techman is offline  
Old 2nd Nov 2021, 1:16 am   #8
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: AVO test leads - bad connections to meter sockets

Quote:
Originally Posted by TowerRadio View Post
You can clean the orifice with contact cleaner on a Q tip,then slightly widen the gap in the plug.Les
That's what I've done. I went out to the workshop and gently clamped each one in a drill stand type vice with a wrap of cardboard for protection (the outside sections of this type of vice offers underside support, unlike a standard vice) and then tapped a thin blade with a small hammer until it split the 'gap' open.

It's now absolutely perfect, I still find it quite surprising that the gap would close up so tightly as to be practically invisible. I've got a few sets of leads from my other older Avos stashed away, so I'll have to get them down off the shelf and check them out for 'slots' - something I should have done in the first place, but I never use the standard Avo leads and particularly those, as they're very old and likely to be a bit 'fragile'. In fact I don't think I've used an Avo with its proper leads since I was a student in the 70s, I've always used them with lead types as shown in the second picture below - it'll make a change to use genuine Avo leads now I've got a 'safe' and reliable set. I realise that as they were, it wouldn't perhaps have affected voltage readings and higher ohms readings, but they really were bad, as you can imagine, with the gap in the plug pin completely closed up like it was.

This is now the newest Avo I've ever had and I don't think I've ever actually used this model before, even at work. It seems strange to have acquired what I would call a 'modern' Avometer. I also got one of those 'Heavy Duty' models from the same place. It has an ancient pair of spade type Avo leads in dubious condition, as you can imagine. This is a model that I've never seen before, but a bit of research shows them to be quite common.

Anyway, it looks like I've got a good usable Avo 8 MK 5, although I notice that the meter needle is out of balance when the meter is stood upright rather than on its back. I also notice that although the low ohms range is now perfect, the reading if left with the probes connected slowly rises, which I'm pretty sure is an indication that the 'D' cell with a date of 06/1997 has a rather high internal resistance, even though the terminal voltage is still good. It rises and then stabilises. I ought to really replace that 'vintage' battery, as I suspect that the date on it was probably around the time that this meter was last used.
Attached Thumbnails
Click image for larger version

Name:	P1140759.jpg
Views:	90
Size:	55.5 KB
ID:	244810   Click image for larger version

Name:	P1140761.jpg
Views:	84
Size:	154.5 KB
ID:	244811  
Techman is offline  
Old 2nd Nov 2021, 8:44 am   #9
Kentode
Octode
 
Kentode's Avatar
 
Join Date: Mar 2015
Location: Yorkshire, England.
Posts: 1,294
Default Re: AVO test leads - bad connections to meter sockets

Quote:
Originally Posted by TowerRadio View Post
You can clean the orifice with contact cleaner on a Q tip...Les
If you're not careful, the cotton bud will be pulled off the end of the tip and remain in the meter socket! Ask me how I know...

Hint: a short length of single core wire with a small hook formed on the end will retrieve it.
__________________
Regards, Ken.

BVWS member
Kentode is offline  
Old 2nd Nov 2021, 2:47 pm   #10
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: AVO test leads - bad connections to meter sockets

I used a cotton bud with IPA in the sockets - luckily the end didn't come off!
Techman is offline  
Old 2nd Nov 2021, 5:47 pm   #11
The Philpott
Dekatron
 
The Philpott's Avatar
 
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,081
Default Re: AVO test leads - bad connections to meter sockets

I think that i have seen one or two of these pins that have started to close up but nothing like that.. Also you get the Avo special trick where when you pull the shrouded lead off the meter the PVC cap lifts off it's splines, sits firmly inside the shroud and refuses to leave!

It's surprises me how much dust and fluff can corrode the insides of the terminals in unboxed meters.
The Philpott is offline  
Old 3rd Nov 2021, 12:19 am   #12
Alistair D
Nonode
 
Alistair D's Avatar
 
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
Default Re: AVO test leads - bad connections to meter sockets

"If you're not careful, the cotton bud will be pulled off the end of the tip and remain in the meter socket! Ask me how I know..."

The ones I am using at the moment are from ASDA. https://groceries.asda.com/product/c.../1000017779777

The adhesion of the tip is excellent and they are as cheap as chips.

Al
__________________
I won't tell you how I discovered that.
Alistair D is offline  
Old 3rd Nov 2021, 2:21 am   #13
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: AVO test leads - bad connections to meter sockets

Yes, I think a lot depends on the 'quality' of the cotton bud

I should clarify the bit I said about the the reading rising on the low ohms range if I leave the probes connected. What is actually happening is that the resistance reading is falling, as setting zero it will actually slowly go beyond the zero, so the chemical action in the very old 'D' cell starts to get going and the cell actually warms up and improves, not the other way round with the voltage decreasing - it needs replacing really, as it may eventually end up leaking.
Techman is offline  
Old 24th Nov 2021, 3:11 pm   #14
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: AVO test leads - bad connections to meter sockets

I dug out my stash of old Avo leads that came with various other meters over the decades and some of them weren't as bad as I'd remembered, so I've found another half decent set. These have a different type of plug with a wrap round sprung type contact that still needed cleaning and bending out a bit on both leads.

I've replaced the 1.5 volt cell, but the adjustment pot was very hit and miss, so I opened the meter up to investigate and possibly clean. What I've actually discovered is that the main problem is due to the riveted connection of the pot tags and not a dirty pot track. Manipulating the tag to rivet connection was making a lot of difference. The pot is a lot better than it was and the low ohms range is now quite usable, but it's by no means perfect. The chips on a couple of corners of the top face of the meter shows that someone who didn't know where the hidden screws were had been in there before. The innards looked in generally good and untouched condition - do you think?
Attached Thumbnails
Click image for larger version

Name:	P1140787.jpg
Views:	70
Size:	114.7 KB
ID:	246491   Click image for larger version

Name:	P1140791.jpg
Views:	52
Size:	101.0 KB
ID:	246492  
Techman is offline  
Old 24th Nov 2021, 4:26 pm   #15
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: AVO test leads - bad connections to meter sockets

Quote:
Originally Posted by Techman View Post
The innards looked in generally good and untouched condition - do you think?
Actually, now I look at the picture that I took when I had it briefly apart, I notice something on the printed circuit shunt in the top right, although the meter works on all ranges and seemed to be near enough within tolerance regarding accuracy. I'm not used to the innards of what I would call a more 'modern' Avo with printed shunts etc.
Techman is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:38 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.