Interesting (?) DME relay discovery...
01-02-2012, 12:13 PM
#1
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Interesting (?) DME relay discovery...
Shortly after I bought my '90 C4 I purchased a spare DME relay from PP based on forum advice. Also on the advice of the forums, I took the functioning DME relay out of the relay block to serve as the spare and plugged the new one in. This was in July IIRC.
Starting in mebbe October or November I started getting rare random no-starts. I never put the original relay back in; a tap on the top of the new relay usually 'fixed' the issue and I'd forget about it until next time. I finally pulled the relay out to have a look at it last night.
(Apologies; my digicam isn't working so you get blackberry images)
Using an illuminated magnifier I found NO issues with the solder pads. No cracks, no cold joints. The PCB looked great.
Flipping the body over I looked at the actual relay mechanisms and that's where I found something interesting.
These are simple devices. There's a pair of electromagnets that when energized pull a 'flapper plate' (that's a technical term
) down to the magnet core. The flappers are held up by a single spring when the magnets are not energized and aren't really 'hinged' by anything other than interlocking shapes of the flapper edge and electromagnet housing. Affixed to the flappers are copper contact plates and welded to those are copper braids which are also welded to the electromagnet body.
In the relay I have, the copper braid on the lower electromagnet was installed in such a way that it was in physical contact with the flapper plate, resulting in that flapper plate not sitting correctly. It wasn't flat to the 'hinge axis' like that of the upper mechanism. It was obvious that the copper braid was clamped to the electromagnet housing prior to welding, and the clamped area remained squashed flat to the housing above the weld. This was where the braid was interfering with the motion of the flapper. I got under the flattened clamp area with a thin wedge (used a scalpel, actually...) and lifted it enough to get a small flathead screwdriver under it. It only took a light pry and gentle rearrangement to get the flapper to sit correctly. Note please that these photos are post-repair.
I did this last night so I can't say for sure that I fixed the problem, but here's hoping...
Starting in mebbe October or November I started getting rare random no-starts. I never put the original relay back in; a tap on the top of the new relay usually 'fixed' the issue and I'd forget about it until next time. I finally pulled the relay out to have a look at it last night.
(Apologies; my digicam isn't working so you get blackberry images)
Using an illuminated magnifier I found NO issues with the solder pads. No cracks, no cold joints. The PCB looked great.
Flipping the body over I looked at the actual relay mechanisms and that's where I found something interesting.
These are simple devices. There's a pair of electromagnets that when energized pull a 'flapper plate' (that's a technical term
) down to the magnet core. The flappers are held up by a single spring when the magnets are not energized and aren't really 'hinged' by anything other than interlocking shapes of the flapper edge and electromagnet housing. Affixed to the flappers are copper contact plates and welded to those are copper braids which are also welded to the electromagnet body. In the relay I have, the copper braid on the lower electromagnet was installed in such a way that it was in physical contact with the flapper plate, resulting in that flapper plate not sitting correctly. It wasn't flat to the 'hinge axis' like that of the upper mechanism. It was obvious that the copper braid was clamped to the electromagnet housing prior to welding, and the clamped area remained squashed flat to the housing above the weld. This was where the braid was interfering with the motion of the flapper. I got under the flattened clamp area with a thin wedge (used a scalpel, actually...) and lifted it enough to get a small flathead screwdriver under it. It only took a light pry and gentle rearrangement to get the flapper to sit correctly. Note please that these photos are post-repair.
I did this last night so I can't say for sure that I fixed the problem, but here's hoping...
01-02-2012, 01:55 PM
#2
RL Technical Advisor
Well done!!!! The quality control of these (and other) parts leave something to be desired and this may become SOP if the situation worsens.
By the powers invested in me by Rennlist, I hereby confer on you the degree of DER; Doctor of Electrical Relays, and that includes all honors and privileges that you are now entitled to.
By the powers invested in me by Rennlist, I hereby confer on you the degree of DER; Doctor of Electrical Relays, and that includes all honors and privileges that you are now entitled to.
01-02-2012, 04:05 PM
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Oh, sure. And you guys call dessert 'pudding', giving rise to this obviously ridiculous conversation:
"Hullo mum! What's for pudding?"
"Oh hi sonny- we'll be having pudding for pudding."
Don't even get me started on bollocks. Something that sucks is 'bollocks' (or 'pants'; wtf?!), but something good is 'the dog's bollocks.'
I'm just messing; work with a mess of Brits and the actual truth is that HRH pays my wage. Thanks for the info!
"Hullo mum! What's for pudding?"
"Oh hi sonny- we'll be having pudding for pudding."
Don't even get me started on bollocks. Something that sucks is 'bollocks' (or 'pants'; wtf?!), but something good is 'the dog's bollocks.'
I'm just messing; work with a mess of Brits and the actual truth is that HRH pays my wage. Thanks for the info!
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01-02-2012, 04:40 PM
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It takes 5 minutes or less to check; my prescription would be to do so before you're stuck roadside. In the dark. While it's cold and raining. And you're headed back to your date's house. (I hate when that happens)
01-02-2012, 06:05 PM
#11
Burning Brakes
Boots and Bonnets and cubby boxes...Oh My
If you dont eat your meat you can't have any pudding...how can you have any pudding if you dont eat your meat
If you dont eat your meat you can't have any pudding...how can you have any pudding if you dont eat your meat
Last edited by Silvertarga; 01-02-2012 at 07:11 PM.
01-02-2012, 06:35 PM
#12
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Project for Feral Comprehension
Feral: Why not construct an electromagnetic device wired to your dash or another handy-dandy arm's-length remote position that has a servo-arm that taps on the top of your DME relay in case you're ever stuck in a midnight heavy downpour, no flashlight, and a burned-out trunk light, or heaven forbid, a broken hood release cable. It could plug into an adjacent site in the central electric panel and take up a minimum of space. I would begin post-haste on a feasibility study ! Having an advanced degree in both cosmic and subatomic electromagnetic phenomena from Ding-Dong University, I am the one to call for any and all assistance you may need. CHEERS.
01-02-2012, 07:02 PM
#13
Burning Brakes
01-03-2012, 06:46 AM
#15
