[Techtoolslist] Used HP 547A to find a pin to trace short

Tue Mar 19 12:52:46 EDT 2019

SnortSniffer is very simular to the AIM unit   ( https://www.testecvw.com/ )

William Stillwell

Board Member - Inspiration labs, Inc. a 501c3 organization

Board Member & Co-Founder - Byte Amusement Group // Free Play Florida
Arcade & Pinball Show a 501c3 organization

On Tue, Mar 19, 2019 at 12:32 PM <wkarkula at comcast.net> wrote:

> That LeakSeeker looks nice.  It's one of those tools that you don't use as
> often but when you need it, it's a godsend and time saver. I have a few
> different tools like that.  I like the audible feedback especially.
> I'd like to have one.
>
>
> -----Original Message-----
> From: Techtoolslist <techtoolslist-bounces at flippers.com> On Behalf Of
> Douglas Gauck via Techtoolslist
> Sent: Tuesday, March 19, 2019 7:47 AM
> To: John Robertson <jrr at flippers.com>; Technical Tools Mail List
> <techtoolslist at flippers.com>
> Cc: Douglas Gauck <douglasgb at mac.com>
> Subject: Re: [Techtoolslist] Used HP 547A to find a pin to trace short
>
> Here are some videos I did about a similar device, the LeakSeeker:
>
> https://www.youtube.com/playlist?list=PLVD-zkkSvyEV3OP-3i9BOrzJPfmWqc7pR
> <https://www.youtube.com/playlist?list=PLVD-zkkSvyEV3OP-3i9BOrzJPfmWqc7pR>
>
> -Douglas
>
> > On Mar 19, 2019, at 3:43 AM, John Robertson <jrr at flippers.com> wrote:
> >
> > On 2019/03/18 11:39 p.m., David Shoemaker wrote:
> >> Have had this item for years and finally figured out what it is good
> for.
> >>
> >>
> >>
> >> Problem 2: No sound
> >>
> >> No sounds at all, but the CPU seemed to be running.  Sounds fine if
> >> putting the rom board on the CH main.  Verified the CPU to be good
> >> and the Sound PAL was also good.
> >>
> >> Started probing around the 74LS244 & 245 and found pin 5 on IC276
> >> ('244) was looking bad.  Grabbed my HP Logic comparator and clipped
> >> it on.  Hit test and Pin 5 bad.
> >>
> >>
> >> As there are no schematics for the System 18 I did some continuity
> >> checking to try to figure out where that pin goes, found it goes to
> >> pin 2 on the sound PAL.  And up to the interconnect for the Rom board.
> >>
> >>
> >> But due to a slipped probe I noticed something else.  I was also
> >> getting continuity at GND (about 175ohm).  And at the +5 rail (3 ohms).
> >>
> >> Bad 244, shorted internally so I clipped pin 5 and checked continuity
> >> again for GND and +5.  Same thing.  BUGGER.
> >>
> >> With the trace damage I had seen I thought there was probably a pin
> >> touching a trace somewhere.  But after more than an hour with a tiny
> >> screwdriver and a magnifier I wasn't any better.
> >>
> >>
> >> Did some YouTube research on tracking down shorts.  Really didn't
> >> like the idea of dropping a few amps down the +5 rail grounded
> >> through the pal pin to try and find something warm.  I don't have a
> >> milliohm meter and they run a couple hundred $.  I do have an ESR
> >> meter which is a small resistance meter but it wasn't high enough
> resolution to find it by probing around the board.
> >>
> >> Found a video on the HP 547A current tracer and using it to track
> >> down
> >> shorts: https://www.youtube.com/watch?v=Verow5aGL0w
> >>
> >> I just so happen to have one of these I bought off ebay years ago
> >> thinking it might be useful in tracking down vector board problems.
> >> But I have never taken it out of the box to date.
> >>
> >> Ran my logic pulsar output into the +5 rail with the ground of it
> >> tied to the sound pal pin 2.  Then I was able to adjust the light on
> >> the 547A to just showing when touching that pin.  Started tracing
> >> around the board and picked up the signal near the connector to the
> >> rom board.  Ran along that area until I found a trace it was running
> >> up and followed it a couple inches then BOOM no more signal.  There
> >> was a chip pin leg right the spot it vanished.  Used my little screw
> >> driver to lift the pin and no more signal on the trace I was following
> and nothing at the pal pin 2.
> >>
> >> Put the rom board back on and sound fixed.
> >>
> >>
> >> Total cost of repair:  < $.50 in kynar wire (not counting the Clutch
> >> Hitter PCB which I will keep as a ref board for the future)
> >>
> >> Total time spent: about 4 hours
> >>
> >
> > I found a device years ago called the Global Specialties 'Short Squeak'
> (manual in the FTP archives - see link below) which produces an audio tone
> that is inversely related to the resistance of the circuit. This is great
> for finding shorts or low resistance loading - mostly under around around 2
> ohms. It looks like a regular probe but has a separate power supply wall
> wart. You hook the common lead to your common point (often ground, but can
> be Vcc, etc.) and then run the probe tip along various circuits listening
> to
> the pitch change, the pitch gets higher as the resistance lowers between
> the
> probe tip and the probe common.
> >
> > ftp://ttl.arcadetech.org/TTL/Test_Equipment/Global%20Specialities/Glob
> > alSpecialities_ShortSqueek_Model_SQ-1.pdf
> > <ftp://ttl.arcadetech.org/TTL/Test_Equipment/Global%20Specialities/Glo
> > balSpecialities_ShortSqueek_Model_SQ-1.pdf>
> >
> > I should make a video of the thing in action I guess, the HP Current
> Probe
> video referenced above, is not bad but I think the Short Squeak could be
> faster...should take it apart and copy out the circuit.
> >
> > John :-#)#
> >
> > --
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