Re: Trying to bring back a AA501

Chuck Harris

I am having trouble imagining how a 15V CMOS device could spontaneously
generate 5V on one of its outputs.... I can see ~0V, or ~15V, or even 7.5V,
but 5V is an odd value for a device that has no resistors in it.

Are you sure that it isn't being bullied around by whatever it is driving?
old style CMOS has very little drive capability.

-Chuck Harris

Eric wrote:

This one did fail the truth table check when it was in the device. VCC is about 15V
which means a HIGH is 15V. Output 3 has a 5V output and does not move from there.
When it should be high it is at 5V when it should be low it is at 5V. In the 501 the
truth table is frequency dependent on the input. As you roll through the frequency
the outputs should do their thing. 1 2 and 4 seem to function as expected.

On 1/5/2020 3:30 PM, KB6NAX wrote:
Watch out! The CD and 74 pinouts are different. You don't what to hack up your
circuit board.

Also, be advised, when troubleshooting IC's in general having the schematic of the
device gives understanding of how inputs and outputs work. For example a tri-state
output could be "off" and not "open." A CMOS input is high impedance so you don't
know if the input stage is blown unless a clamp diode is shorted. The ultimate is
to try the truth table, a lot of work on complex parts. Parts substitution can't
be beat for getting results. I always buy two or more when in that situation.

eBay to the rescue - Item #372418190226


-----Original Message----- From: Eric
Sent: Sunday, January 05, 2020 6:51 AM
Subject: Re: [TekScopes] Trying to bring back a AA501

I did find out that the AA501 does need the VCC of 15V so the HC series
logic is out for sure. I am going to order some of the direct
replacement parts as there is a supply house that has then mouser and
digikey were out. Texas Instrument cross reference says a CD40175BE is a
comparable part as well. I have also confirmed the fault as with this IC
out of circuit the 501 says 100+% distortion on all frequencies also one
of the outputs is open when i check it with my small curve tracer. On
this one pin 14 is dead.

On 1/5/2020 1:08 AM, KeepIt SimpleStupid via Groups.Io wrote:
My GOTO place has it:
On Saturday, January 4, 2020, 10:31:47 PM EST, Mlynch001
<@mlynch001> wrote:
OK, learned something. LSTTL and TTL are different animals? SN74HC175N Will
drive 10 outputs of LSTTL. Just trying to learn how logic works, I will likely
encounter a similar issue in the future.


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