DIY-WB LED problem (KC-5300 display)

[Crescent Kao]

> That leaves the VR3 resistor divider network or the op-amp. Notice
> I said in the unity gain buffer that pin 1 follows pin 3, check
> that it does, if not then the op-amp is the problem, otherwise
> figure out what's wrong w/ the divider.

Ok.. I continued with the testing today with the information you've
provided. With pin 1 and 2 jumped, I tested the voltage at pin 1 with 12v
applied to the circuit. Again, the values were from 0.63v - 0.85v  when
adjusting VR3 (however it wasn't stable this time - it would fluctuate
slightly... yesterday it was rock solid). Probing pin 3, i would get
"similar" voltages, however it seemed to be about 0.1v lower (on average)
than at pin 1.. again the voltate was fluctuating slightly during the
measuring where it was rock solid yesterday.

Also, Peter mentioned in another email to check if the Dimmer circuit it
functioning correctly. Well as far as I can tell it is working. However from
the brightest to the dimmest setting, the different isn't that much... and
when VR1 is turned all the way down, the display instantly shut off and does
not display anything. Not sure if that means anything.

> "Proof of this theorem is left as an exercise for the student"
>
> Good luck, and let us know the answer.

hehe.. pretty optimistic, I have very limited electrical experience. All I
know how to do is solder and recognize symbols and diagrams from the few EE
classes that I've taken. My area of expertise is Industrial Design and
Computer Science where I have a B.S. in both. Your help is very much
appreciated - makes me wish I payed more attention in class 8)


Crescent Kao
Director of Marketing and Sales
www.c-speedracing.com


----- Original Message -----
From: "Phil Hunter" <ilphayunterhay at yahoo.com>
To: <diy_efi at diy-efi.org>
Sent: Monday, January 21, 2002 10:02 AM
Subject: Re: DIY-WB LED problem (KC-5300 display)


> [snip]
> > I just performed the test you described. With IC1 removed and
> > in 1 and 2 jumped on IC2 (IC2 still in place), when I vary VR3,
> > I get a voltage range of 0.63v - 0.85v  With the jumper removed
> > and pin 1 jumpered to the sensor input, when I vary VR3, I get
> > a voltage range of 1.97v - 2.65v
>
> [snip]
>
> > Perhaps I have the trim pots at VR2 and VR3 wrong? The
> > pot at VR3 is currently labelled 502 and VR2 is labelled 254.
>
> One way to read this is 50 and 2 more 0's, i.e. 50 & 00 or
> 5000, 25 and 4 more 0's, 25 & 0000 or 250K, so you have them
> correct.
>
> At this point, you should have enough info to figure out the
> problem if you think about it. The pin 1 voltages don't match
> what was predicted, but in the 3X amp configuration they are
> about 3 times the unity gain configuration, so the sensor input
> circuitry (the difference in the 2 configurations) s/b correct.
> That leaves the VR3 resistor divider network or the op-amp. Notice
> I said in the unity gain buffer that pin 1 follows pin 3, check
> that it does, if not then the op-amp is the problem, otherwise
> figure out what's wrong w/ the divider.
>
> "Proof of this theorem is left as an exercise for the student"
>
> Good luck, and let us know the answer.
>
> regards,
> philh
> (digest)
>
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