How tolerant is VB921?

hobieboy · Post by **hobieboy** » Tue Aug 01, 2006 8:41 pm

Well - my ignition saga goes on & I thought I'll go back to basic and test the VB921's - apply 5V via 330ohm to pin 1 and see if pin 2 & 3 have continuity.

What was working last night is now not working. Pull out a new VB921, did the test - worked. Fiddle with the board. Went back to test the new VB921. Now it is NOT working - no continuity.

Did I do something wrong or are these really that finicky?

I am stumped... and please tell me I should not give up

Post by **jsmcortina** » Wed Aug 02, 2006 4:33 am

Checking for continuity isn't how I would test it. Apply a decent load to it - like a car light bulb or similar. i.e. +12v -> bulb -> VB921 -> ground
Then apply 5v to the base.

James

hobieboy · Post by **hobieboy** » Wed Aug 02, 2006 5:07 am

James, you are right - must be too late last night. Zero load may not work.
And yes, just confirmed that I did have 2 dead VB921 that corresponds to me not seeing spark from those 2.

THANKS!

Now looking forward - how do I "debug" starting problem if I have fuel & spark and car won't start? Where do I look - MT? MSLVV? ???

Post by **jsmcortina** » Wed Aug 02, 2006 5:30 am

If you have fuel and spark it is back to the basics like trying to start any car. Is the spark happening at the right time - test with a strobe. Are you getting the right amount of fuel? Check plugs to see if they are wet fouled and/or try some easy start spray.

James

ptegler · Post by **ptegler** » Wed Aug 02, 2006 7:44 am

If you think you might have damaged a VB921 but it still
seemd like it's working... an ohmmeter CAN be used to
check them. From Base to drain you'll see less than 100K
ohm if its bad or damaged. If good, it'll read >80
megaohms
btdt. YES...you CAN statically zap the base inputs.
They'll still trigger, but not at full power.

ptegler

On Wed, 02 Aug 2006 04:33:11 -0700
"jsmcortina" <jsm@jsm-net.demon.co.uk> wrote:

Checking for continuity isn't how I would test it. Apply
a decent load to it - like a car light bulb or similar.
i.e. +12v -> bulb -> VB921 -> ground
Then apply 5v to the base.

James

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hobieboy · Post by **hobieboy** » Wed Aug 02, 2006 9:52 pm

Hi Peter, I have ohm-ed all the suspected ones. And the one that was confirmed dead has ~0 ohm across B-E junction. So its definitely dead. The read all read >20M ohms (that's all my small meter can tell).