Heathkit oscilloscope?

[Dan Beck]

Hello all,

I have been fooling (emphasis on fool) with an old Heathkit 10 MHz two
channel oscilloscope, which I believe was built in 1976 (it was given to me
several years ago). I have been able to calibrate the voltage on one
channel, but not the other. Sometimes, after I have spent some time probing
old pinball machine circuit boards using the one good channel, the voltage
flakes out such that there is minimal amplitude in the waveform, and I can
no longer observe good signals from the board in test.

Does anyone here have experience with such a dinosaur? When the device
works it has helped me diagnose these old boards; I am just wondering if
there are any tips from the wisemen here in order for me to set this thing
up better, recalibrate, etc.

Thank you in advance for reading.

Regards,
Dan

 

[Michael A. Terrell]

Hello all,

I have been fooling (emphasis on fool) with an old Heathkit 10 MHz two
channel oscilloscope, which I believe was built in 1976 (it was given to me
several years ago). I have been able to calibrate the voltage on one
channel, but not the other. Sometimes, after I have spent some time probing
old pinball machine circuit boards using the one good channel, the voltage
flakes out such that there is minimal amplitude in the waveform, and I can
no longer observe good signals from the board in test.

Does anyone here have experience with such a dinosaur? When the device
works it has helped me diagnose these old boards; I am just wondering if
there are any tips from the wisemen here in order for me to set this thing
up better, recalibrate, etc.

Does this scope have a model number?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Rick]

Does this scope have a model number?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I'm thinking the IO-4510 or 20..

 

[robb]

Hello all,

I have been fooling (emphasis on fool) with an old Heathkit 10 MHz two
channel oscilloscope, which I believe was built in 1976 (it was given to me
several years ago). I have been able to calibrate the voltage on one
channel, but not the other. Sometimes, after I have spent some time probing
old pinball machine circuit boards using the one good channel, the voltage
flakes out such that there is minimal amplitude in the waveform, and I can
no longer observe good signals from the board in test.

Does anyone here have experience with such a dinosaur? When the device
works it has helped me diagnose these old boards; I am just wondering if
there are any tips from the wisemen here in order for me to set this thing
up better, recalibrate, etc.

Thank you in advance for reading.

I assembled one of those in college as part of a physics
project. 10 years later i purchased at an alumni day /reunion lab
clearout sale. It came with the original assembly instructions
manual, schematics and user manual. I also see these on THe-bay
occasionally.

if you have trouble solving problem, can not find info already
posted somewhere , and i have the same model them let me what you
need i can try to post something somewhere.

robb

 

[Dan Beck]

Thank you all for the responses!

I apologize for omitting the model number. It is a Heathkit IO-4550 two
channel oscilloscope. The individual who gave it to me also built it, so I
have all the assembly and operation manuals.

Another flaky behavior is when I connect to the 1 V peak-to-peak calibrator
on the front, I do get the square wave, but sometimes it only lasts for a
few seconds, and then the voltage craps out and I lose the waveform
amplitude, as I discussed previously.

Could any of these symptoms be explained by dried out electrolytic
capacitors? I also noticed when I was attempting to calibrate the second
channel's voltage (the one that doesn't work at all) the potentiometer I was
supposed to turn was sticky, and rough feeling.

Again, thank you in advance for any and all responses!

Regards,
Dan

 

[Michael Black]

Thank you all for the responses!

I apologize for omitting the model number. It is a Heathkit IO-4550 two
channel oscilloscope. The individual who gave it to me also built it, so I
have all the assembly and operation manuals.

Another flaky behavior is when I connect to the 1 V peak-to-peak calibrator
on the front, I do get the square wave, but sometimes it only lasts for a
few seconds, and then the voltage craps out and I lose the waveform
amplitude, as I discussed previously.

Have you made sure the probe (including the cable and connector) are
actually good? If any of that was flakey, the amplitude would suddenly
go away. And sometimes it's worth looking at the simplest solutions.

Just use a piece of wire to connect the input to the calibrator output,
and see what happens.

Michael

 

[Dan Beck]

Hi Michael,

thank you for your comments. Yes, indeed it is profitable to keep things
simple...Here are some observations:

Y1 (Good channel) Using a plain wire per your suggestion reveals a stable
square wave of appropriate amplitude, with the following exception. If I
gently tap the AC-GND-DC switch for that channel, without even changing the
position of the switch, the waveform decays to a trace with noise. This new
trace looks like it's "trying" to return to a square wave, but doesn't. If
I rapidly move the switch up and down it usually corrects; otherwise I have
to power down the 'scope and return to it minutes later.

Y2 (Bad channel) Using the plain wire test again all I get is a trace with
noise on it, very similar to what I described above. Messing with the
corresponding AC-GND-DC switch does nothing.Sometimes I am able to use this
channel to read signals from one of my circuit boards, but the amplitudes
are much lower than they should be, given the voltages I expect them to be
at.

I was able to perform the compensation procedure for the probe on its 10X
setting, using the supplied calibrator square wave on the 'scope, so I think
it is safe to conclude the probe is ok.

Both AC-GND-DC switches feel sloppy in their respective actions; I wonder if
they need attention...

I do appreciate your efforts with this.

Regards,
Dan

 

[Peter Bennett]

Hi Michael,

thank you for your comments. Yes, indeed it is profitable to keep things
simple...Here are some observations:

Y1 (Good channel) Using a plain wire per your suggestion reveals a stable
square wave of appropriate amplitude, with the following exception. If I
gently tap the AC-GND-DC switch for that channel, without even changing the
position of the switch, the waveform decays to a trace with noise. This new
trace looks like it's "trying" to return to a square wave, but doesn't. If
I rapidly move the switch up and down it usually corrects; otherwise I have
to power down the 'scope and return to it minutes later.

My first thought would be dirty switch contacts, but the power off/on
remedy confuses things. Could also be a cold solder joint on the
switch connections.

Y2 (Bad channel) Using the plain wire test again all I get is a trace with
noise on it, very similar to what I described above. Messing with the
corresponding AC-GND-DC switch does nothing.Sometimes I am able to use this
channel to read signals from one of my circuit boards, but the amplitudes
are much lower than they should be, given the voltages I expect them to be
at.

Possibly poor connections to/around the gain switch/pot.

You could try connecting corresponding points in the two channels
while feeding one channel - that may help to locate the fault in the
bad channel.

Of course, once you have one channel working fairly well, you can use
it to trace the signal through the bad channel.

If the original builder wasn't too experienced soldering, you should
check carefully for cold solder joints.

 

[Rich Grise]

I apologize for omitting the model number. It is a Heathkit IO-4550 two
channel oscilloscope. The individual who gave it to me also built it,
so I have all the assembly and operation manuals.

Another flaky behavior is when I connect to the 1 V peak-to-peak
calibrator on the front, I do get the square wave, but sometimes it only
lasts for a few seconds, and then the voltage craps out and I lose the
waveform amplitude, as I discussed previously.

When you say, "the voltage craps out", which voltage do you mean? Knowing
that will go a very long way toward helping us help you troubleshoot
this thing.

Good Luck!
Rich

 

[robb]

Thank you all for the responses!

I apologize for omitting the model number. It is a Heathkit IO-4550 two
channel oscilloscope. The individual who gave it to me also built it, so I
have all the assembly and operation manuals.

you are quite fortuneate to have those...

have you already run the initial diagnostic setup tests ? how
accurate were the voltages and resistances at the test points ?
were any out of the specified range ?

I have a note in the margin of ny manual that says "No trace"
even though only a few of the values were slightly out of
specified range

Another flaky behavior is when I connect to the 1 V peak-to-peak calibrator
on the front, I do get the square wave, but sometimes it only lasts for a
few seconds, and then the voltage craps out and I lose the waveform
amplitude, as I discussed previously.

I am no expert buy any stretch but the little i have leaned,
flaky electronic behavior seems accompanied by some physical
connection problem (i like the poor solder joint idea from one
of te experts) or possibly a close but not exact component
substitution

since it was a kit i would worry about incorrect connections,
swapped or in correct components placement. Looking inside, i
remember how easy it was to make incorrect connections on the
switches, using the wrong valued parts (resistors / transistors )
and putting the parts in the wrong place etc...

i am sure i overheated several parts soldering / de-soldering /
re-soldering.

Could any of these symptoms be explained by dried out electrolytic
capacitors? I also noticed when I was attempting to calibrate the second
channel's voltage (the one that doesn't work at all) the potentiometer I was
supposed to turn was sticky, and rough feeling.

scope seems like a restoration project in-itself.
sounds like fun
robb

 

[Dan Beck]

Hello all,

many thanks for all the responses to my questions. They are very much
appreciated, and more importantly, learned, where I had to learn!

An update: I reflowed the solders on the BNC connectors for both probes,
and the solders on the AC-GND-DC switches. I also tried to clean out these
switches using solvent on a cotton swap. Both switches are improved, but
one still exhibits flakiness. I have new switches on order. As for the BNC
connectors, the connector for the dead trace I had turned out to be the
problem. Both traces work properly now, with appropriate amplitudes.

Regards,
Dan

 

[Rich Grise]

many thanks for all the responses to my questions. They are very much
appreciated, and more importantly, learned, where I had to learn!

An update: I reflowed the solders on the BNC connectors for both
probes, and the solders on the AC-GND-DC switches. I also tried to
clean out these switches using solvent on a cotton swap. Both switches
are improved, but one still exhibits flakiness. I have new switches on
order. As for the BNC connectors, the connector for the dead trace I
had turned out to be the problem. Both traces work properly now, with
appropriate amplitudes.

Cool!

But bottom-posting is the convention.

Cheers!
Rich