Tektronix 2245; need help with dead PSU

A

Alfred Green

Guest
Greetings,

My 2245 'scope recently died, with no outputs from the psu. The input
cct seems ok with ~150vdc across the filter cap, but I'm having a hard
time tracing the voltages any further without a schematic.
Does anyone have such a thing, and/or tips on what to be looking for?
In case there are different versions, the psu board has a 1986 date
code and uses a MC34060 pwm chip.

All comments welcome,

Alf in Scottsdale, AZ
nu8i@cox.net
 
nu8i@cox.net (Alfred Green) wrote in
news:cc6cad33.0310201756.497cf208@posting.google.com:

Greetings,

My 2245 'scope recently died, with no outputs from the psu. The input
cct seems ok with ~150vdc across the filter cap, but I'm having a hard
time tracing the voltages any further without a schematic.
Does anyone have such a thing, and/or tips on what to be looking for?
In case there are different versions, the psu board has a 1986 date
code and uses a MC34060 pwm chip.

All comments welcome,

Alf in Scottsdale, AZ
nu8i@cox.net
Click to expand...
ISTR that the 2245 service manual has schematics for the PS.
Ebay or big-list.com may turn up a manual.
And you can download a datasheet for the Motorola MC34060 IC probably at
the Motorola website.
You can ohm the switcher FET (open?)and any rectifier diodes(short?),check
the electrolytics with an ESR meter.

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
I might be able to help.
i have a manual for something like this.
might just be the same one.
will let you know later.



"Alfred Green" <nu8i@cox.net> wrote in message
news:cc6cad33.0310201756.497cf208@posting.google.com...
Greetings,

My 2245 'scope recently died, with no outputs from the psu. The input
cct seems ok with ~150vdc across the filter cap, but I'm having a hard
time tracing the voltages any further without a schematic.
Does anyone have such a thing, and/or tips on what to be looking for?
In case there are different versions, the psu board has a 1986 date
code and uses a MC34060 pwm chip.

All comments welcome,

Alf in Scottsdale, AZ
nu8i@cox.net
Click to expand...
 
"Jim Yanik" <jyanik@abuse.gov> wrote >
ISTR that the 2245 service manual has schematics for the PS.
Ebay or big-list.com may turn up a manual.
Click to expand...
I spoke to someone at Tektronix and he confirmed that the service manual
does include the schematics. They no longer have anything available however.
A net search has failed to uncover one either so far. I have found one for
the 2246; I wonder if it used the same psu as the 2245.

And you can download a datasheet for the Motorola MC34060 IC probably at
the Motorola website.
Click to expand...
I have that info. Checking the vcc wrt the ground pin shows the voltage
varying from 0 to +5v; lower than I was expecting and I'm puzzled why it
would be changing.

You can ohm the switcher FET (open?)and any rectifier diodes(short?),check
the electrolytics with an ESR meter.
Click to expand...
The input switcher is an IRF830 which I think is enhancement mode, so I cant
really check that without supplying gate voltage. The diodes and caps seem
ok, but testing them in-circuit could be misleading.

I'll keep on exploring, and I appreciate the comments.

Rgds, Alf
Scottsdale AZ
nu8i@cox.net
 
I found my Service manual and its for a 2445A


"Alfred Green" <nu8i@cox.net> wrote in message
news:cc6cad33.0310201756.497cf208@posting.google.com...
Greetings,

My 2245 'scope recently died, with no outputs from the psu. The input
cct seems ok with ~150vdc across the filter cap, but I'm having a hard
time tracing the voltages any further without a schematic.
Does anyone have such a thing, and/or tips on what to be looking for?
In case there are different versions, the psu board has a 1986 date
code and uses a MC34060 pwm chip.

All comments welcome,

Alf in Scottsdale, AZ
nu8i@cox.net
Click to expand...
 
"Alfred Green" <nu8i@cox.net> wrote in
news:luilb.104366$gv5.59425@fed1read05:

"Jim Yanik" <jyanik@abuse.gov> wrote
ISTR that the 2245 service manual has schematics for the PS.
Ebay or big-list.com may turn up a manual.

I spoke to someone at Tektronix and he confirmed that the service
manual does include the schematics. They no longer have anything
available however. A net search has failed to uncover one either so
far. I have found one for the 2246; I wonder if it used the same psu
as the 2245.
Click to expand...
Yes,it does.(I coulda told you TEK would nothave the manual;the 224X series
has been 'obsolete',or past the 'Long Term Support Period' for several
years now.)
And you can download a datasheet for the Motorola MC34060 IC probably
at the Motorola website.

I have that info. Checking the vcc wrt the ground pin shows the
voltage varying from 0 to +5v; lower than I was expecting and I'm
puzzled why it would be changing.
Click to expand...
The 'housekeeping' supply for the IC is started by a cap charged by a
resistor from the rectified line V supply.The cap charges,the IC tries to
start,but the xfmr winding that maintains the 'houskeeping' supply cannot
supply current,perhaps because the switcher FET is open.
You can ohm the switcher FET (open?)and any rectifier
diodes(short?),check the electrolytics with an ESR meter.

The input switcher is an IRF830 which I think is enhancement mode, so
I cant really check that without supplying gate voltage. The diodes
and caps seem ok, but testing them in-circuit could be misleading.
Click to expand...
That ESR meter (Dick Smith meter!!) is invaluable for testing in-circuit
electrolytics,especially for switcher supplies.
I'll keep on exploring, and I appreciate the comments.

Rgds, Alf
Scottsdale AZ
nu8i@cox.net
Click to expand...


--
Jim Yanik,NRA member
jyanik-at-kua.net
 
"Techie" <Jbtek@Optonline.net> wrote in
news:ccllb.29478$6j.3827009@news4.srv.hcvlny.cv.net:

I found my Service manual and its for a 2445A
Click to expand...


Not the same family of scopes. No similarity at all.

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns941BEFDD0B44Ajyanikkuanet@204.117.192.21...
"Alfred Green" <nu8i@cox.net> wrote
far. I have found one for the 2246; I wonder if it used the same psu
as the 2245.

Yes,it does
Click to expand...
Thanks. I've ordered a CD for the 2246.

The 'housekeeping' supply for the IC is started by a cap charged by a
resistor from the rectified line V supply.The cap charges,the IC tries to
start,but the xfmr winding that maintains the 'houskeeping' supply cannot
supply current,perhaps because the switcher FET is open.
Click to expand...
That makes sense. I'll dig out one of my old scopes to look at it, just
using a DVM may be giving me a false picture.
I may just replace the FET anyway and see what happens.

That ESR meter (Dick Smith meter!!) is invaluable for testing in-circuit
electrolytics,especially for switcher supplies.
Click to expand...
Sounds like a good investment!

Tnx, Alf
 
"Techie" <Jbtek@Optonline.net> wrote
I found my Service manual and its for a 2445A
Click to expand...
It looks like there are some similarities, but not quite enough. I
appreciate your efforts in sending me the diagram; I'll keep it for future
reference.

Tnx, Alf
 
"Alfred Green" <nu8i@cox.net> wrote in
news:qbylb.106325$gv5.565@fed1read05:

"Techie" <Jbtek@Optonline.net> wrote
I found my Service manual and its for a 2445A


It looks like there are some similarities, but not quite enough. I
appreciate your efforts in sending me the diagram; I'll keep it for
future reference.

Tnx, Alf
Click to expand...
The 2245 and the 2445 and A versions are nothing alike.
Two entirely different families. Different architectures.
Now,2445 and 2465 (and A,B versions)are very similar;and 2245 and 2246,2247
are very similar.

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
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