TEK 221 O-Scope Power Supply Problems

Group,
I have a "dead" TEK 221 scope that I am trying to repair. Nothing out of the power supply. The batteries are dead, so I removed them. Will the power supply operate without the batteries, power by the AC Line? Can I operate the power supply out of the scope (disconnected from the scope)? I cannot find any indication that the first inverter is running. Checked transistors OK. I suspect that the inverter trigger diac is defective. No way to test.
Please share any thoughts that you have or past experiences.
Thank you,
Dave

 

[Jeff Liebermann]

On Thu, 11 Sep 2014 08:50:12 -0700 (PDT), davidahoneycutt@gmail.com
wrote:

>I have a "dead" TEK 221 scope that I am trying to repair. Nothing out of the power supply. The batteries are dead, so I removed them. Will the power supply operate without the batteries, power by the AC Line? Can I operate the power supply out of the scope (disconnected from the scope)? I cannot find any indication that the first inverter is running. Checked transistors OK. I suspect that the inverter trigger diac is defective. No way to test.

I have an earlier Tek 213 scope that had a similar problem when I
bought it:
<http://802.11junk.com/jeffl/pics/drivel/slides/tek213.html>
The problem was that some of the "D" size NiCd batteries were shorted.
With the batteries shorted, dead, or missing, the AC power supply
would not run. I suspect that the 221 might have a similar design and
problem:
<http://www.eevblog.com/forum/repair/oscilloscope-for-electronics-repair/msg98150/?PHPSESSID=a6693dbf5ce85bb11009cfdd0688449b#msg98150>


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[mike]

On 9/11/2014 8:50 AM, davidahoneycutt@gmail.com wrote:

Group,
I have a "dead" TEK 221 scope that I am trying to repair. Nothing out of the power supply. The batteries are dead, so I removed them. Will the power supply operate without the batteries, power by the AC Line? Can I operate the power supply out of the scope (disconnected from the scope)? I cannot find any indication that the first inverter is running. Checked transistors OK. I suspect that the inverter trigger diac is defective. No way to test.
Please share any thoughts that you have or past experiences.
Thank you,
Dave

I got my manual from here
http://manoman.sqhill.com/
It's a locked pdf, so I can't cut/paste from it.
and it's 91MB.

The miniscope series has weird power supply configurations.
This one shuts down if the battery voltage is below 10.3V.
Don't try to run it with the battery disconnected...it's a critical
part of the regulator.
It's 10 NiCd A-cells, but they're only 600 mAH. Should run fine on
more modern AA NiCd's.
Should also run on NiMH, but the charger will probably kill them
with overcharge if you leave it connected to AC.

Be careful probing around in there.
There are connections between the line side and the isolated side that
you'd not expect without a schematic.
And some things that you might think were ground referenced aren't.

Don't want to smoke your
scope probe or yourself.

 

[Maynard A. Philbrook Jr.]

In article <f0947de3-acb8-40d7-9cea-fcf9e425faaf@googlegroups.com>,
davidahoneycutt@gmail.com says...

Group,
I have a "dead" TEK 221 scope that I am trying to repair. Nothing out of the power supply. The batteries are dead, so I removed them. Will the power supply operate without the batteries, power by the AC Line? Can I operate the power supply out of the scope (disconnected from the scope)? I cannot find any indication that the first inverter is running. Checked transistors OK. I suspect that the inverter trigger diac is defective. No way to test.
Please share any thoughts that you have or past experiences.
Thank you,
Dave

If I am not mistaken, those supplies work like some UPS supplies and if
the battery is no good or missing, it won't start.

Normally there is some sort of slow charge and once the batteries get
up to snuff, the inverter will start.

Not sure if using an external supply is going to allow
you to test for this? Some charging circuits and supplies
are smart and test the condition of the batteries. You
may need to put a resistor in series to fake it if you
attempt an external supply test in place of the batteries.

Jamie

 

[chuck]

On Thu, 11 Sep 2014 08:50:12 -0700 (PDT), davidahoneycutt@gmail.com
wrote:

Group,
I have a "dead" TEK 221 scope that I am trying to repair. Nothing out of the power supply. The batteries are dead, so I removed them. Will the power supply operate without the batteries, power by the AC Line? Can I operate the power supply out of the scope (disconnected from the scope)? I cannot find any indication that the first inverter is running. Checked transistors OK. I suspect that the inverter trigger diac is defective. No way to test.
Please share any thoughts that you have or past experiences.
Thank you,
Dave

I have a 212 on my bench and it definitely will not work without a
good battery pack. I rebuilt the battery pack and still had a
problem. Some diode in the power supply area had also failed but I
can't remember which one. Chuck