[Diy_efi] FW: WB testing problems - again

[Stephen Andersen]

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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