[Diy_efi] FW: WB testing problems - again

[rr]

Best bet is to lower the value of R38. It is a 100K now. Reduce it
to 75K or so. Not critical. This portion of the circuit is an anti-glitch
filter. Or can lower the value of C12. Try a 2 to 2.2 uf. Just need to
get the voltage at U3 pin 5 higher.

BobR.


Stephen Andersen wrote:

> I'll try this again since I have not seen it yet...
>
> Okay, I have done more testing.
>
> Bottom line is that C12 IS leaking.  When I disconnect it (at the
> + terminal) everything goes to 7.75-7.8 volts, particularly
> terminal 5 of U3.
>
> So, now, what is the solution to this?  I had already replaced
> the cap itself with no change.  Any ideas?  What will this affect?
>
> I am not going to continue the rest of the tests until I
> understand the impact of this problem a bit better.
>
> Any ideas?
>
> Thanks,
> Steve
>
> > -----Original Message-----
> > From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
> > Behalf Of bcroe at juno.com
> > Sent: Sunday, April 14, 2002 3:37 PM
> > To: Stephen Andersen; bcroe at juno.com
> > Cc: diy_efi at diy-efi.org; RRauscher at nni.com
> > Subject: WB testing problems
> >
> >
> > Steve,
> >
> > Sounds like the meter is OK.
> >
> > With 7.8 V on the +4 side of R38, there must be leakage
> > on the other side pulling it down to 6.75V.  Check first for
> > solder splashes to that wire.  Assuming no shorts, there
> > are 3 parts that could cause the leakage.  Those are
> > ISO1 at pin 4, C12 at plus, and U3B at pin 5.
> >
> > As a check against reversed parts, move the probe from
> > R38 to those pins.  Count from the dot on the case to pin
> > 4 of ISO1 and expect the same 6.75 V.  Do this at pin 5
> > of U3 and the PLUS terminal of C12.  If you see a different
> > voltage, the part might be reversed.
> >
> > If that checks out, certainly do BobRs test of shorting ISO1
> > pin 1 to pin 2.  If this fixes the problem, Q1 may be leaking.
> > Try shorting Q1 pin 1 and 2 together; if that gives you 8V at
> > R38, Q1 is leaking.  I would suggest reducing R1 to 33K
> > and see if it is cured.
> >
> > If all that fails, you could remove the 3 parts one at a time
> > until R38 goes to 8V.  As BobR suggested, disconnect
> > C12 first as most likely suspect.  I would disconnect
> > ISO1 next, and then U3 pin 5.  Sometimes you can just
> > cut the pin, then bridge the cut with solder when the bad
> > part is found.  Its a good idea to check each cut with an
> > ohmmeter to make sure its really cut, or use your volt
> > meter to see a different voltage on each side running.
> >
> > Bruce Roe
> >
> >
>
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