[sdiy] VCO Problems

[mikko.a.helin at nokia.com]

Let's see, if you use 12V supply the comparator should fire at 1/3 * 12V =
4V, and the output stage for saw doubles it and offsets to zero, so you
should get 8V p-p voltage. Measure also the CA3140 (integrator) output. If
it's >=4 V there's problem with the comparator/Schmitt trigger and FET as
the cap in integrator is not discharged properly. If you haven't done it yet
do it now: take some isopropanyl (for an example car windscreen cleaning
stuff or gasoline antifreezing stuff sold in gas stations, you must know it
if you've got the 4-wheel thing) and clean the pcb properly. It may be that
the pulse meant to set the FET on is not hold long enough (it's upto the 18p
cap and 15k resistor to make the time constant for the LM311 long enough to
completely discharge the cap) (if you can get a scope use it to see the
LM311 and CA3140 outputs for wave formats and time constant). Also double
check the FET type, it should be N-type enhancement FET. 

-Mikko

-----Original Message-----
From: ext Juho Lepistö [mailto:juho.lepisto at pp.inet.fi]
Sent: 08. December 2001 17:57
To: Diy
Subject: [sdiy] VCO Problems


I bet I'll get loads of "What did I said" messages.
Ok... My ASM VCO is silent. I've checked the connections and transistor/fet
polarities. Everything seems to be ok but still I don't get any signals out.
I'll get -8V out from saw output and -2V out from pulse output. I think the
problem might be my 12V power. I know that ASM is for 15V. Does ASM work
with 12V without component changes or do I have to change any component
values or is my project doomed?

P.S. Answer is still no. I don't want to buy kits even this is tough. I like
challenges.