DAN COTSIRILOS" <[EMAIL PROTECTED]>
Dan,
as i got the below respond from your email provider (for
whatever reason, i do not know - i use a serious german
email account powered by an t-online server, which is not
suspected to distribute junk or spam-mail), i post my
answer back to you on this public platform - if you want
to go private, please give me an email adress that works
without such annoying refusement messages).
The original message was received at Wed, 10 Mar 2004 22:27:27 +0100
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Betreff:
Re: [drakelist] FS-4
Datum:
Wed, 10 Mar 2004 22:26:49 +0100
Von:
Herbert Schulz <[EMAIL PROTECTED]>
An:
DAN COTSIRILOS <[EMAIL PROTECTED]>
Referenzen:
1
Dan,
for first, there is a question: are you well eqipped with measure-
ment tools for fixing that problem? It is likely, that you need
some advanced measurement rig's - the minumum i would recommend
is an analog scope with a MINIMUM bandwith of 150[MHz] (like vin-
tage Tektronix or HP scopes) with approbriate, high frequency and
low capacity 10:1 probes as well as a reliable, accurate frequency
counter with a minimum of 80[Mhz] measurement range....the second
point is, that most of the integrated circuit stuff used in the
FS-4 is no longer available today, but you may need the one or
other chip just for cross checking....
Now, for the details:
- Is the +5[V] and +12[V] DC supply really stable with no more
than appr. 50...100[mVpp] max. ripple and noise?
- Can you measure a stable sine-wave signal of 9.600[MHz] on test-
point "A" (testpoint "A" is the junction between R416 (470[Ohm])
and C418(0.001[µF])? What is the amplitude (pk-pk)
of that signal?
You have to measure it with a 10:1 probe with no more than
appr.
5[pF] load capacity. This measurement should be independent
of
any switch setting.
- Can you measure a stable sine wave signal of 5.000[MHz] at the
junction of C301 and C302? Or, as an alternative, measure
this
signal at the base of Q302 (2N3563). This signal should
be in
the range of several ten's to hundred's [mVpp]. However,
please
note, that capacitive loading of the probe is even more
critical
at that points, so that i would recommend a probe with a
capa-
citive load of no more then appr. 2[pf]. This measurement
also
should be independent of any switch setting. This measurement
point is located on the "A300 digital board".
- What does the input signal of U1(SN7490) at pin 1 look alike?
Ideally, it should be a waveform shape that at low goes
well
beyond appr. 700[mV] and where the high exceeds significantly
over appr. 2.4[V]. Also here, measure with a very low capacity
probe and a SHORT ground lead, otherwise you will see ringing
and other "hard to read" effects in the signal. This measurement
also should be independent of any switch setting. This measurement
point is also located on the "A300 digital board".
- Does the output signal of U1(SN7490) - a 10:1 frequency divider
-
present a true TTL-square-wave-signal (1:1 duty cycle) with
a
frequency of 500.00[kHz] and a amplitude low of 400[mV]
maximum
as well as a amplitude high of 2.8[V] minimum? Again, also
here
a low capacitance probe as well as a short ground lead is
man-
datory. Also here, this is a measurement that is independent
of any switch setting. As well as the above, also this measurement
point is located on the "A300 digital board".
- What is the voltage on the collector of Q202 (2N3563) are looking
alike in terms of frequency and amplitude? THIS IS A CRITICAL
POINT
TO MEASURE IN TERMS OF LOADING THROUGH THE PROBE! This measurement
point is located on the "A200 Locked Oscillator Board".
These are the tests for the moment. We will go one step further
if these tests are in all details prove to be o.k.
Kind regards and enjoy your evening as well as 73
Herbert, DG7MCC
