Channel A failure on Tek 2235

T

Terry Ilardi

Guest
I have a Tek 2235 scope (military version) on which I suddenly lost the
A channel. I get a nice flatline trace for channel A. The B channel
works fine.

I need to troubleshoot this but was looking for suggestions as to where
to start. It went out quite suddenly (I was switching the test leads
from from A to B and then back to A when it happened). I was wondering
if the failure might have been induced by a static discharge.

If anyone knows of typical components in this scope that are likely to
fail and cause this problem, I would appreciate hearing from you. Also,
since I don't have a spare scope to troubleshoot with, if anyone has any
suggestions as to how I should proceed with just a DVM, signal generator
and other typical test equipment, I would appreciate it.

Thanks.

Terry Ilardi
 
Terry Ilardi <ilardi@us.ibm.com> wrote in
news:c1votg$gao$1@news.btv.ibm.com:

I have a Tek 2235 scope (military version) on which I suddenly lost the
A channel. I get a nice flatline trace for channel A. The B channel
works fine.

I need to troubleshoot this but was looking for suggestions as to where
to start. It went out quite suddenly (I was switching the test leads
from from A to B and then back to A when it happened). I was wondering
if the failure might have been induced by a static discharge.

If anyone knows of typical components in this scope that are likely to
fail and cause this problem, I would appreciate hearing from you. Also,
since I don't have a spare scope to troubleshoot with, if anyone has any
suggestions as to how I should proceed with just a DVM, signal generator
and other typical test equipment, I would appreciate it.

Thanks.

Terry Ilardi
Click to expand...
First,take off the cabinet,and see if there's a broken BNC-PCB connection.
(wire,solder joint) Or even a bad Ch.1 BNC(bad center receptacle)
Then maybe you could have a bad AC-GND-DC switch. Jumper around it,see if
you get a signal then.
If you blew up the input FETs,you would have a DC offset on Ch.1.A DMM
would allow you to check the input FET pair for that offset.


--
Jim Yanik
jyanik-at-kua.net
 
Jim Yanik wrote:

Terry Ilardi <ilardi@us.ibm.com> wrote in
news:c1votg$gao$1@news.btv.ibm.com:


I have a Tek 2235 scope (military version) on which I suddenly lost the
A channel. ...

Thanks.

Terry Ilardi



First,take off the cabinet,and see if there's a broken BNC-PCB connection.
(wire,solder joint) Or even a bad Ch.1 BNC(bad center receptacle)
Then maybe you could have a bad AC-GND-DC switch. Jumper around it,see if
you get a signal then.
If you blew up the input FETs,you would have a DC offset on Ch.1.A DMM
would allow you to check the input FET pair for that offset.


Thanks. Will try. The bad connector sounds like a possibility since,
Click to expand...
now that I think about it, Channel A has been a little flakey in the
past. I always thought it was my fault due to poor setup.

By the way, I've read that the 2235 was not one of Tektronix' better
products. Do you know anything about that?

Thanks again for the help.

Terry Ilardi
 
Terry Ilardi <ilardi@us.ibm.com> wrote in
news:c2295s$7mk$1@news.btv.ibm.com:

Jim Yanik wrote:

Terry Ilardi <ilardi@us.ibm.com> wrote in
news:c1votg$gao$1@news.btv.ibm.com:


I have a Tek 2235 scope (military version) on which I suddenly lost
the A channel. ...

Thanks.

Terry Ilardi



First,take off the cabinet,and see if there's a broken BNC-PCB
connection. (wire,solder joint) Or even a bad Ch.1 BNC(bad center
receptacle) Then maybe you could have a bad AC-GND-DC switch. Jumper
around it,see if you get a signal then.
If you blew up the input FETs,you would have a DC offset on Ch.1.A
DMM would allow you to check the input FET pair for that offset.


Thanks. Will try. The bad connector sounds like a possibility since,
now that I think about it, Channel A has been a little flakey in the
past. I always thought it was my fault due to poor setup.

By the way, I've read that the 2235 was not one of Tektronix' better
products. Do you know anything about that?

Thanks again for the help.

Terry Ilardi
Click to expand...
2235,2236 IMO were very good scopes,although not comparable to a 465 or
465B.The 2200 series was designed to be low-cost,high-volume manufacturing.

The 2245 series was not very good,IMO.
300 series were garbage(Sony-Tek)

I have a 2213,myself(built from scratch! I repaired PCBs other techs had
scrapped,bought the mech parts I couldn't salvage(less than $50),and got
Vern Isaacs of CRT manufacturingto give me a new CRT that was graded OK but
only for internal use.

--
Jim Yanik
jyanik-at-kua.net
 
Jim is the resident expert on Tek scopes. I agree with him; check the
mechanical connection on the BNC connector center pin. There is a
carbon comp resistor that connects the center pin of the BNC to the
attenuator PCB. Check that resistor & it's connections to the
connector and PCB.

I actually think the 2235 is a good scope. More cheaply made than the
400 series, yes, but they were like half the price when new. I use a
2235A as my main troubleshooting scope & have fixed a couple dozen
2235's.

BTW, you can use your scope to check itself! You don'e need a spare
to troubleshoot this type of problem. What I mean is that you can
feed a signal into channel A, and use channel B to troubleshoot the
signal thru the attenuator to see where the problem lies. Be careful
when you have the cover off, of course!

Jeff

On Mon, 01 Mar 2004 11:38:07 -0500, Terry Ilardi <ilardi@us.ibm.com>
wrote:

I have a Tek 2235 scope (military version) on which I suddenly lost the
A channel. I get a nice flatline trace for channel A. The B channel
works fine.

I need to troubleshoot this but was looking for suggestions as to where
to start. It went out quite suddenly (I was switching the test leads
from from A to B and then back to A when it happened). I was wondering
if the failure might have been induced by a static discharge.

If anyone knows of typical components in this scope that are likely to
fail and cause this problem, I would appreciate hearing from you. Also,
since I don't have a spare scope to troubleshoot with, if anyone has any
suggestions as to how I should proceed with just a DVM, signal generator
and other typical test equipment, I would appreciate it.

Thanks.

Terry Ilardi
Click to expand...
 
Jim Yanik wrote:

I have a 2213,myself(built from scratch! I repaired PCBs other techs had
scrapped,bought the mech parts I couldn't salvage(less than $50),and got
Vern Isaacs of CRT manufacturingto give me a new CRT that was graded OK but
only for internal use.
Click to expand...
Very cool! I once built an Eico 460 (not quite the same-but hey, I was
sixteen at the time).

Terry Ilardi
 
Jeff W wrote:

Jim is the resident expert on Tek scopes. I agree with him; check the
mechanical connection on the BNC connector center pin. There is a
carbon comp resistor that connects the center pin of the BNC to the
attenuator PCB. Check that resistor & it's connections to the
connector and PCB.

I actually think the 2235 is a good scope. More cheaply made than the
400 series, yes, but they were like half the price when new. I use a
2235A as my main troubleshooting scope & have fixed a couple dozen
2235's.

BTW, you can use your scope to check itself! You don'e need a spare
to troubleshoot this type of problem. What I mean is that you can
feed a signal into channel A, and use channel B to troubleshoot the
signal thru the attenuator to see where the problem lies. Be careful
when you have the cover off, of course!

Jeff

Jef,
Click to expand...

Thanks. I had thought of trying to use the good channel to troubleshoot
the bad but then decided I was deluding myself that it could be done.
It's nice to hear the experts say that it is possible. If its more then
a bad connection (I can use my DVM for that) I'll try it.

Thanks.

Terry Ilardi
 
"Terry Ilardi" <ilardi@us.ibm.com> wrote in message
news:c1votg$gao$1@news.btv.ibm.com...
I have a Tek 2235 scope (military version) on which I suddenly lost the
A channel. I get a nice flatline trace for channel A. The B channel
works fine.

Terry - When you say "Channel A" or "Channel B", I presume you mean Channel
Click to expand...
1 or 2. "A" and "B" refer to the timebases, so check that you have selected
"Horizontal Mode A" for the timebase, and that the outer timebase knob is
engaged with the lower. For the "Vertical Mode" select BOTH and CHOP. Do
both VERTICAL POSITION controls work? If they do, the pre-amplifier is ok;
if not, compare the voltages around the Ch.1 pre-amp U130 (M84F), Q114+115
with CH.2 pre-amp U180, Q164+165. Your 'test signal' here is the position
controls! Also check the switching voltages at Pin 14 of U130+180; according
to the service manual, should be +0.7V to switch that channel ON, -0.7V for
OFF.

If position controls are ok, switch vert mode to ADD and see if you get a
signal through each channel. If not, look first at the attenuators, then at
the buffer amps and phase splitters on the attenuator PCB. The buffer amps
are U10 (CA3180), Q13+15+18, the phase splitter is U30 for Ch.1, U60,
Q63+65+68, U80 for Ch.2. Compare DC voltages, or trace an AF signal from
your sig gen, listening with any small audio amp but with a 100nF capacitor
to block DC.

HTH - Julian (Manchester, UK)
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top