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# Suitable transient voltage suppression diode

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## Suitable transient voltage suppression diode

(OP)
I have a 1992 Dodge Stealth with a relay that no longer works, The circuit is fused for 15 amps and is 12 volts. After some investigation I have determined that a transient voltage suppression diode, which was soldered into the relay, is open. This very tiny diode has the number 77 on it and also has the number 1 then a dot followed by what appears to be the capital letter I (eye). Can a replacement diode suitable for this circuit be recommended? Any help is appreciated

### RE: Suitable transient voltage suppression diode

Any 1n4001 series or higher should work. Is this in series with the relay? Just wondering because an open suppression diode would not prevent the relay from operating. Ford has a diode in series with a relay to prevent damage to electronics should a battery be connected in reverse. Many automotive relays now just use resistors in parallel with the coil for suppression.

### RE: Suitable transient voltage suppression diode

You probably already did, but just to make sure...

### RE: Suitable transient voltage suppression diode

(OP)
The coil with the double winding runs the fuel pump. The coil with the diode runs the idle control servo motor, the purge control solenoid, and the air temperature sensor. I have the factory service manual for this car and in it there is a very detailed description on how to test this relay. The particular check that this relay fails is: Connect the positive pole of the voltage source to pin #10, connect the negative pole of the voltage source to pin #8 and use a voltmeter across pins #4 and #5. The volt meter should show the source voltage. When I connect pins #10 and #8 The contacts can be heard as a "click" but the volt meter reads Zero volts. I perform this and the other checks inside my house using connectors I assembled. I purchased 2 brand new relays and both failed this very same check and were never installed in the car. They showed up bad. The relay has a cover which is not all that securely attached so I removed it from my relay to see what was inside just for the heck of it. I used an ohm meter to check the coils and all other possible junctions inside the relay and appropriate resistance was found. I then decided to remove the diode and measured its resistance in both directions. I found resistance way 1.5 million ohms indicating an open diode. That is my story and pretty everything I know about this relay. What problems there were with the 2 new relays I purchased I do not know for sure other than zero volts across pins #4 and #5 when there should have been 12 volts. Many thanks once again for all the responses. Ultimately I hope to repair this relay as there is only 1 company still making them, Standard Motor Parts and they are getting them out of China.

### RE: Suitable transient voltage suppression diode

There seems to be something wrong in your description. Assuming that the contacts are 4 and 5, if they are closed, you should not be able to measure 12V across them because they should be shorted. It's extremely unlikely that you would get 2 brand relays that can't operate correctly. The fact that the contacts are moving basically says they're working correctly. Therefore, the test procedure is not correct, or the interpretation is not correct.

Do you have a schematic drawing of the relay along with the test procedure in PDF form?

TTFN
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### RE: Suitable transient voltage suppression diode

I understand this is frustrating for you, but I would bet what little reputation I have here that the three relays you tested are good. I rebuilt an automatic transmission and that manual had several errors. I would take a step back and rethink this.

### RE: Suitable transient voltage suppression diode

Hi

Any time you connect probes across a closed contact you will see voltage drop, 0V is good.
Black test probe to neg. supply and red probe to either pin 8or10 to read source voltage maybe.

Chuck

### RE: Suitable transient voltage suppression diode

Note that some DMMs do not generate sufficient voltage necessary to read diodes. The typical DMM has a specific test range for diodes, usually marked with the diode symbol. ONLY that range will give the correct reading for a diode.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

### RE: Suitable transient voltage suppression diode

(OP)
I do not have the schematic or instructions for testing in PDF form. I tested the diode in the proper selection on my DMM. Pins #4 and #5 are continuous with each other so reading 12 volts across is proper. About a year ago I had another electrical issue with this car and during my investigation I tested this relay and, at that time, it tested good doing the very same tests I have described. I found it hard to believe that 2 new relays would both test bad, but this is a double relay with 2 coils and the other coil tests just like it is supposed to. I am confident in my findings but not comfortable telling a manufacturer the problems I have encountered. This relay is not your usual situation. Again, thank you for replying and efforts to help me. I can scan the pages in my factory service manual and save them as a jpeg. Would that help?

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