[Diy_efi] DIY-WB construction & testing... help

[Andrew Brownsword]

>>>> The UEGO circuit fails two tests:  pin 5 of U3 measures 7.2v instead of 7.8
>>>> - 8.0, and J5 measures 1.8v instead of 1.9 - 2.1.
>>> 
>>> For U3 pin 5 lift one leg of the cap C12 and re-measure. IF the voltage
>>> goes up that cap is leaky.
>> 
>> The voltage didn't change, so the capacitor would seem to not be the
>> culprit.  Any other suggestions?  Is it related to the J5 voltage problem?
> 
> Have you cleaned the flux off the board yet?

I cleaned off one particularly bad area using a chemical "pen".  Should I do
a more extensive pass?  Can flux cause shorts?
 

>>> J5 should really be closer to 2 volts. Is the +4 volt (VGnd) measurement
>>> on the low side? This would contribute to a low J5 reading. If not then
>>> double check the resistors R31, R32 & R35; as to being 1% to and 10K &
>>> 100K.
>> 
>> The VGnd voltage is about 3.95v -- so it is on the low side.  Could this be
>> a result of my power supply being on the 12.5v?  Does it matter?  Those 3
>> resistors are all very close to their target values (<0.5% error).
> 
> 3.95v is at 1.25%, darn good. Lets see, 1.8v/2.0v = 10%. That is why I
> believe it should be higher. Maybe check the specs on the DVM you are
> using. It may be loading the circuit.

Hmmm.  Unfortunately I don't have the manual for this unit anymore.  Its a
Sperry DM-4100A... nothing fancy just your basic DVM.  Should I go and
invest in something better?  Recommendations?
 
 
> You can try the tests, if they wwork good. If not, then do not worry
> about it.

Heh, this seems like an interesting testing policy.  :)

Cheers,
  Andrew


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