telford dorr
Samba Member
Joined: March 11, 2009
Posts: 3555
Location: San Diego (Encinitas)
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 Posted: Fri Dec 11, 2020 4:46 pm Post subject: Another Way to Fix a 9-pin Relay |
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[From the "Out on the Fringe of Reality" department]
Did a repair for someone the other day, and wound up with an old 12 volt 9-pin flasher relay (used in 67 to 69 bus). The unit worked OK on the turn and brake functions, but bench testing showed it failed in the 4-way flash mode - VL terminal for the front left turn light produced no output.
Now the normal way to fix this is to buy a new one, but this was an otherwise good OG relay, and it seemed wasteful to just throw it away. So I opted for a repair. Because the relay contacts in this model relay are well hidden, the normal way to do this is to drill out the long rivet in the mounting foot, then remove the guts and work on them. This leaves you with a relay that works, but needs a through bolt to hold it together (viable, but not desirable).
Thinking about this for a minute, I realized that because the 4-way flasher function is hardly ever used, the relay contacts could easily oxidize or otherwise crud up. Maybe just operating this thing repeatedly for a while would mechanically wipe the contacts clean. Worth a try, except I didn't want to sit there for an hour turning this thing on an off. So I came up with Plan B.
Having a tube of these lying around, I used a AtTiny85 microcontroller to repeatedly turn a transistor (2N3055 / equiv) on and off twice a second. [AtTint85 has to be the most useful chip since the 555 timer, but any Arduino board would work..) Took a few miscellaneous parts plus a page of code to get the job done. Hooked it all up, gave the relay a shot of contact cleaner spray, and set it running. Within 10 minutes, a test light hooked to the VL terminal started blinking. Ran it for a half an hour just to make sure it was clean.
"But wait a minute!", you say, "Where am I supposed to get a AtTiny85 microcontroller? And write the code? That's not my thing..."
"That's not the point", I reply. "It's not how you do it, it's what was done that's important". For me, the microcontroller was the easiest way. But you could just as easily cobb up a second turn signal flasher of some kind to drive a Bosch cube relay, and use the Bosch relay to repeatedly ground the "S" terminal on the 9-pin relay. Same results.
[For those interested, the code I use is shown below:]
| Code: |
/*
9-pin Relay Exerciser
Revisions: 12/11/20 - initial release
This sketch is used to repeatedly operate the 4-way relay in a VW
9-pin turn signal relay. The theory is, because this relay is seldom
operated, the relay contacts oxidize and fail to close. Because the
relay is difficult to take apart (involves drilling out a large rivet),
an alternate cleaning method is desired. This sketch mechanically wears
the relay contacts to remove the oxides.
*/
/*
Note: unless modified, the AtTiny defaults to a 1 mhz clock. If you
set a different clock in the chip config, you must "burn boot loader".
This does not actually burn a boot loader, but does set the chip clock
fuses. After this, upload the sketch and the timing will be correct.
*/
// Definitions and equates
#define ON HIGH
#define OFF LOW
// Constants
const int RELAY_DRIVE = 2; // pin 7
const unsigned long ON_DELAY = 250; // milliseconds
const unsigned long OFF_DELAY = 250; // milliseconds
void setup()
{
pinMode( RELAY_DRIVE,OUTPUT );
digitalWrite( RELAY_DRIVE,OFF );
}
void loop()
{
digitalWrite( RELAY_DRIVE,ON );
delay( ON_DELAY );
digitalWrite( RELAY_DRIVE,OFF );
delay( OFF_DELAY );
}
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_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST) |
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telford dorr
Samba Member
Joined: March 11, 2009
Posts: 3555
Location: San Diego (Encinitas)
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| Posted: Sat Dec 12, 2020 10:57 pm Post subject: Re: Another Way to Fix a 9-pin Relay |
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Interesting! I never learned the hand signal version of the 4-way flasher mode. But then again, most cars didn't have 4-way flashers when I started driving.
I imagine doing a hand signal 4-way flash could get tedious... 
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST) |
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