[928uk] 1981 - headlight double relay question

[Paul R Smith]

Or, it could be a "logic" diode so that the bulbs aren't powered until 
the lamps are in the upright position but the relaycoil cant put any 
power "back" to the lifting motor.

Smiffy

On 21/01/2023 17:42, Jonathan Rackowe via 928uk wrote:
> If the diode was across the coil (solenoid) of the component relay it was probably a back EMF protection diode. The cheap 1N4148 diode is often used for this purpose, and it is glass encapsulated so that may well have been your diode. A general purpose power diode such as an 1N4001, 1N4002, 1N4003, 1N4004 would work just as well, and as these are rated for higher current than the 1N4148 would probably be a better bet. Note that you must fit the diode the right way round!
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> If the diode was carrying current for headlights it would need a much higher capacity than the 1A diodes listed above – over 10A to support 120W of headlights. Seems unlikely that that was a 10A rated diode though, so I don’t think it was carrying the headlights current.
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> The odd thing was that you say the headlights stopped providing light. That suggests to me more than just the diode having failed. Perhaps the coil failed and that was what took out the diode. What ‘fettling’ did you do that has brought the relay back to life?
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> Do you know enough electronics to work out how the diode was connected in relation to the component relays, and thus what its purpose was?
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> Best regards,
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> Jonathan
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> 928 GT 1991 Amethyst Metallic
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> From: Rob Bocock<robbobrizzle at gmail.com>  
> Sent: 21 January 2023 12:40
> To:jonathan at rackowe.net
> Cc: 928UK List<928uk at lists.928.org.uk>
> Subject: Re: [928uk] 1981 - headlight double relay question
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> Many thanks Jonathan, a bit of fettling has brought it back to life, but It’s no doubt a sign it’s on the way out.
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> On closer inspection, I think it is a glass diode, just struggling to work out its value, so I can get a replacement to solder in.
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> Kind regards
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> Rob
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> Sent from my iPhone
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> On 21 Jan 2023, at 11:13,jonathan at netvue.co.uk  <mailto:jonathan at netvue.co.uk>   wrote:
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> Hi Rob,
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> Are you sure that the blown component was a resistor? In your photo the shiny look and short length make it look rather like a blown glass-encapsulated diode. But maybe the glazed look is just because it’s a resistor that overheated.
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> Unfortunately, I don’t have a 928 618 107 00 or 928 618 107 02 relay to check. Your best bet is to borrow or buy another relay, and then you can check the component type and value, repair your damaged relay and sell it on. These relays are rare so, whatever you do, don’t throw this old one away.
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> Best regards,
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> Jonathan
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> From: Rob Bocock <robbobrizzle at gmail.com  <mailto:robbobrizzle at gmail.com>  >
> Sent: 19 January 2023 15:05
> To:jonathan at rackowe.net  <mailto:jonathan at rackowe.net>  
> Subject: Re: [928uk] 1981 - headlight double relay question
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> Thanks Jonathan
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> Rather irritatingly, I’ve put the relay cover “somewhere safe” and can’t currently locate it.
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> Sadly I can’t see enough colour bands to work out the value either.
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> <image007.jpg>
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> <image008.jpg>
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> <image009.jpg>
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> 1st pic - top left
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> 3rd pic - In line to solenoid top left
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> Kind regards
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> Rob
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> Sent from my iPhone
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> On 19 Jan 2023, at 14:33,jonathan at netvue.co.uk  <mailto:jonathan at netvue.co.uk>   wrote:
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> Hi Rob,
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> Is your relay 928 618 107 00 ?
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> Can you see any coloured rings on the resistor? If so, please list the colours in order, starting at one end or the other.
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> If you can email me a photo that would be good.
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> Best regards,
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> Jonathan
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> 928 GT 1991 Amethyst Metallic
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> From: 928uk <928uk-bounces at lists.928.org.uk  <mailto:928uk-bounces at lists.928.org.uk>  > On Behalf Of Rob Bocock via 928uk
> Sent: 19 January 2023 14:25
> To: 928uk List <928uk at lists.928.org.uk  <mailto:928uk at lists.928.org.uk>  >
> Subject: [928uk] 1981 - headlight double relay question
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> Does anyone happen to know the value of the (I think resistor) soldered on the opposite side of the PCB to the 3 solenoids?
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> It’s the one to the solenoid which sends power to the headlight bulbs.
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> Mine appears to have melted, resulting in all headlight functions apart from light..!
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> Thanks in anticipation.
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> Rob
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> Sent from my iPhone
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