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Hi List

I *know* this is a Tek list - so this is off topic. However, I was so
pleased to have sorted out a problem on my HP 5328A timer I just had to crow
a little.

Ever since I got it, some of the funtions didn't work well (like time
interval and ratio). However, when frequency and period measurement died
too it was clearly time to do something about it. Now this counter cost me
???22 (around $30) on eBay, so it owed me nothing - but I'm a determined cuss
and rarely admit defeat.

Followed around 3 days of diagnostics - derailed by errors in the manual
(the military version). Eventually it turned out to be a chip on the
Function Selector card - labelled Time Base Multiplexer. Now this was a
7454, now obsolete. So having dug out the chip, isolated the output pin and
confirmed that it was indeed *that* chip (and not the one it was driving
holding its output low) I was then confronted with what to do.

Now the chip is a bunch of ANDs and a NOR that does /(AB + CD + EF + GH).
So it would have been possible to replace it with a 7400 and a 4-input NOR -
except that there is no 4-input NOR in fast TTL, just in slow CMOS (and this
chip has to handle a PLL synthesised 100MHz clock). So I transformed the
logic funtion to /(AB)./(CD)./(EF)./GH and used a 74F00 (quad 2-input NAND)
and 74ALS21 (dual 4-input AND), strung together in place of the original
7454.

Works an absolute treat!

Cheers

Craig

Hello Craig,

You might want to consider using a wire-OR of 2-input open collector NANDs,
e.g. 74LS38. It is still a kludge but it is only one IC with few wires and a
flying resistor. If you place a socket on the circuit board and use one of
those 'discrete component adapters' you can do whole thing without cutting
original board.

While on the subject of strange ICs, does anyone know what are Tek's
155-0015-01 and 155-0038-01; the latter is used in 7M13, a Readout Unit, a
plug in that puts text on the screen of 7000 scope.

Regards
Miroslav Pokorni

The Tek P/N 155-0015-01 is a TTL BCD-to-Decimal
converter. My cross reference doesn't say exactly
which one, but it is probably a 7441, 7442, or 7445.
The 155-0038-01 is a 16 pin D/A TTL converter. No
other info.

Craig: The 7454 is obsolete but is still available
from surplus dealers for about $1 US.

Jim Reese

--- Miroslav Pokorni <mpokorni2000@...> wrote:

Hello Craig,

You might want to consider using a wire-OR of
2-input open collector NANDs,
e.g. 74LS38. It is still a kludge but it is only one
IC with few wires and a
flying resistor. If you place a socket on the
circuit board and use one of
those 'discrete component adapters' you can do whole
thing without cutting
original board.

While on the subject of strange ICs, does anyone
know what are Tek's
155-0015-01 and 155-0038-01; the latter is used in
7M13, a Readout Unit, a
plug in that puts text on the screen of 7000 scope.

Regards
Miroslav Pokorni

----- Original Message -----
From: "Craig Sawyers"
<c.sawyers@...>
To: <TekScopes@...>
Sent: Thursday, January 24, 2002 12:39 AM
Subject: [TekScopes] HP counter - off topic

Hi List

I *know* this is a Tek list - so this is off

topic. However, I was so

pleased to have sorted out a problem on my HP

5328A timer I just had to
crow

a little.

Ever since I got it, some of the funtions didn't

work well (like time

interval and ratio). However, when frequency and

period measurement died

too it was clearly time to do something about it.

Now this counter cost
me

?22 (around $30) on eBay, so it owed me nothing -

but I'm a determined
cuss

and rarely admit defeat.

Followed around 3 days of diagnostics - derailed

by errors in the manual

(the military version). Eventually it turned out

to be a chip on the

Function Selector card - labelled Time Base

Multiplexer. Now this was a

7454, now obsolete. So having dug out the chip,

isolated the output pin
and

confirmed that it was indeed *that* chip (and not

the one it was driving

holding its output low) I was then confronted with

what to do.

Now the chip is a bunch of ANDs and a NOR that

does /(AB + CD + EF + GH).

So it would have been possible to replace it with

a 7400 and a 4-input
NOR -

except that there is no 4-input NOR in fast TTL,

just in slow CMOS (and
this

chip has to handle a PLL synthesised 100MHz

clock). So I transformed the

logic funtion to /(AB)./(CD)./(EF)./GH and used a

74F00 (quad 2-input
NAND)

and 74ALS21 (dual 4-input AND), strung together in

place of the original

7454.

Works an absolute treat!

Cheers

Craig

__________________________________________________
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Great stuff seeking new owners in Yahoo! Auctions!

All Tek IC's beginning with the "155-" prefix are Tek-made and there really
are no equals made by any other company. Tek always preferred to buy parts
whenever possible and only made parts in-house when they could not find an
oustside source for them.

Stan
w7ni@...

Jim Reese wrote: