Tektronix 7603 won't trigger

[GanjaTron]

Greetings all,

a question for anyone familiar with the Tektronix 7000 series scopes:

I recently acquired one of these equipped with a 7A24 & 7A12 dual
trace amps plus a 7B53A timebase. The scope powers up with readout but
doesn't show a trace, even with signal input. The trigger blinkenlight
on the timebase doesn't budge (I assume it's supposed to).

Compressing the trace using the beam finder, I found a stationary
blinking (at high time/div settings) spot way off to the right. I can
shift it vertically with the trace amp's position knobs, but that's
it. No trace.

I've got the service manual here and the power supply checks out ok.
The calibration and troubleshooting and procedures didn't help.

I suspect the timebase is trashed and should be replaced. Before I do
that, and since I'm not inclined to invest a significant sum into such
an old scope (despite the praises that have been sung about it in this
newsgroup), I'd like to hear your opinions. If the mainframe's at
fault, I'd probably just sell it off for parts.

Thanks for your time,

--Roland

 

[N_Cook]

GanjaTron <ganjatron@gmx.net> wrote in message
news:972c3117-870a-41fa-b7ca-4e9f41ac06a7@r34g2000vba.googlegroups.com...

Greetings all,

a question for anyone familiar with the Tektronix 7000 series scopes:

I recently acquired one of these equipped with a 7A24 & 7A12 dual
trace amps plus a 7B53A timebase. The scope powers up with readout but
doesn't show a trace, even with signal input. The trigger blinkenlight
on the timebase doesn't budge (I assume it's supposed to).

Compressing the trace using the beam finder, I found a stationary
blinking (at high time/div settings) spot way off to the right. I can
shift it vertically with the trace amp's position knobs, but that's
it. No trace.

I've got the service manual here and the power supply checks out ok.
The calibration and troubleshooting and procedures didn't help.

I suspect the timebase is trashed and should be replaced. Before I do
that, and since I'm not inclined to invest a significant sum into such
an old scope (despite the praises that have been sung about it in this
newsgroup), I'd like to hear your opinions. If the mainframe's at
fault, I'd probably just sell it off for parts.

Thanks for your time,

--Roland

failure in one of the X-driver transistor tails?



--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Jim Yanik]

"N_Cook" <diverse@tcp.co.uk> wrote in news:gv0pjf$tqr$1@news.eternal-
september.org:

GanjaTron <ganjatron@gmx.net> wrote in message
news:972c3117-870a-41fa-b7ca-4e9f41ac06a7@r34g2000vba.googlegroups.com...
Greetings all,

a question for anyone familiar with the Tektronix 7000 series scopes:

I recently acquired one of these equipped with a 7A24 & 7A12 dual
trace amps plus a 7B53A timebase. The scope powers up with readout but
doesn't show a trace, even with signal input. The trigger blinkenlight
on the timebase doesn't budge (I assume it's supposed to).

Compressing the trace using the beam finder, I found a stationary
blinking (at high time/div settings) spot way off to the right. I can
shift it vertically with the trace amp's position knobs, but that's
it. No trace.

I've got the service manual here and the power supply checks out ok.
The calibration and troubleshooting and procedures didn't help.

I suspect the timebase is trashed and should be replaced.

Or repaired. get a 7B53A service manual.

Before I do
that, and since I'm not inclined to invest a significant sum into such
an old scope (despite the praises that have been sung about it in this
newsgroup), I'd like to hear your opinions. If the mainframe's at
fault, I'd probably just sell it off for parts.

Thanks for your time,

--Roland


failure in one of the X-driver transistor tails?



--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

7600's are known for cracks on the regulator PCB,around the TO-3 studs
where they solder to the PCB pads.
also,aging 7600's have PS filter cap problems.

also,metal film resistors in the output amps often change value or open.

You have to check for a ramp coming out of the 7B53A,need that for a sweep
on the display.
It would help to have a different timebase to swap in to see where the
problem is.
Or you could put one of the vert PIs in the H slot and feed in a ramp or
triangle waveform from a function gen.
even a sine wave would work,to see if the MF is OK.

it's also possible the sweep control IC,155-0049-xx has failed.
155-0049-02 ICs are preferable,but -00 and -01 will work.

FYI,you can check date codes on various ICs and other parts to see when
your scope was made. format 8644 would be year 86,week 44

check a couple of PCBs because board-swapping is common.

--
Jim Yanik
jyanik
at
kua.net

 

[PeterD]

On Wed, 20 May 2009 03:48:11 -0700 (PDT), GanjaTron
<ganjatron@gmx.net> wrote:

Greetings all,

a question for anyone familiar with the Tektronix 7000 series scopes:

I recently acquired one of these equipped with a 7A24 & 7A12 dual
trace amps plus a 7B53A timebase. The scope powers up with readout but
doesn't show a trace, even with signal input. The trigger blinkenlight
on the timebase doesn't budge (I assume it's supposed to).

Compressing the trace using the beam finder, I found a stationary
blinking (at high time/div settings) spot way off to the right. I can
shift it vertically with the trace amp's position knobs, but that's
it. No trace.

I've got the service manual here and the power supply checks out ok.
The calibration and troubleshooting and procedures didn't help.

I suspect the timebase is trashed and should be replaced. Before I do
that, and since I'm not inclined to invest a significant sum into such
an old scope (despite the praises that have been sung about it in this
newsgroup), I'd like to hear your opinions. If the mainframe's at
fault, I'd probably just sell it off for parts.

Thanks for your time,

--Roland

See if you can borrow another timebase locally... That would be a
quick diagnostic. If the timebase module is what is bad (probably is,
but that's a WAG!) then you can get 'em on eBay for a low amount. I
could even be convinced to send you one though shipping would be
expensive...

 

[GanjaTron]

On May 20, 2:55 pm, Jim Yanik <jya...@abuse.gov> wrote:

"N_Cook" <dive...@tcp.co.uk> wrote innews:gv0pjf$tqr$1@news.eternal-
september.org:

it's also possible the sweep control IC,155-0049-xx has failed.
155-0049-02 ICs are preferable,but -00 and -01 will work.

Well, I got hold of a service manual and traced through the timebase
with another working scope. Turns out the fault is on the horizontal
preamp board, specifically one or both of the CA3046 xsistor arrays. I
found the CA3086 as a readily available replacement in a cross ref, so
I'll see how that goes.

Btw, the 7B53 isn't exactly cheap in Germany (not that anything else
is). You can expect to pay up to 5-fold compared to the States for a
used plugin on eBay.

 

[msg]

GanjaTron wrote:

Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

FWIW, some 7603s were for sale for $10 at a local hamfest a few years
ago and I believe that all of them had a bad can electrolytic in the
power supply; the one I bought sure did and replacing it brought
the scope to life but I too have complaints about noise (not flickering)
on the trace with no input (7A18 dual trace vert). I have not
investigated any capacitor issues in the plugins or elsewhere in the
mainframe. Triggering worked for me.

Michael

 

[Jeff Liebermann]

On Thu, 18 Jun 2009 13:57:43 -0500, msg <msg@_cybertheque.org_> wrote:

GanjaTron wrote:

Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

FWIW, some 7603s were for sale for $10 at a local hamfest a few years
ago and I believe that all of them had a bad can electrolytic in the
power supply; the one I bought sure did and replacing it brought
the scope to life but I too have complaints about noise (not flickering)
on the trace with no input (7A18 dual trace vert). I have not
investigated any capacitor issues in the plugins or elsewhere in the
mainframe. Triggering worked for me.

Michael

Yep. I have a Tek 7623A storage scope, with 7A12 vertical and 7B53A
sweep plugins. Lots of tiny push buttons to keep me entertained.
However, I had to go through a pile of about 10 such mainframes before
I found one that didn't have blown electrolytics in the power supply.
I dragged home the one and only working one from the pile, ran it for
about 2 months, and the canned electrolytics blew up.

Moral: If the cans are not blown now, they will be shortly.
Pre-emptive replacement might a useful exercise.

--
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

 

[GanjaTron]

Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

Regards,

--Roland

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
newsu6l35d3mt8ruv9d66b3imb28in12u06hg@4ax.com:

On Thu, 18 Jun 2009 13:57:43 -0500, msg <msg@_cybertheque.org_> wrote:

GanjaTron wrote:

Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

FWIW, some 7603s were for sale for $10 at a local hamfest a few years
ago and I believe that all of them had a bad can electrolytic in the
power supply; the one I bought sure did and replacing it brought
the scope to life but I too have complaints about noise (not flickering)
on the trace with no input (7A18 dual trace vert). I have not
investigated any capacitor issues in the plugins or elsewhere in the
mainframe. Triggering worked for me.

Michael

Yep. I have a Tek 7623A storage scope, with 7A12 vertical and 7B53A
sweep plugins. Lots of tiny push buttons to keep me entertained.
However, I had to go through a pile of about 10 such mainframes before
I found one that didn't have blown electrolytics in the power supply.
I dragged home the one and only working one from the pile, ran it for
about 2 months, and the canned electrolytics blew up.

Moral: If the cans are not blown now, they will be shortly.
Pre-emptive replacement might a useful exercise.

heh,more than 10 years ago,I was replacing 7600 series PS filter caps
because they were drying out/low capacitance.(at TEK-Orlando)

there's also some electrolytic caps on the mainframe interface board that
affect PS operation.
Also,the studs that the TO-3 xstrs screw into develop cracks around the
solder pin(from thermal cycling).I used to file off the chrome plating
on the pin,then resolder them all,and the socket for the transistor array
on the +5V supply gets removed and the array soldered in.(TEK official mod)

One real worry is "gold-dot" connectors on the ribbon cables;
there was a mandatory mod to replace all G-D ribbon cables on all 7000
series scopes that had them. they caused a lot of intermittents.
they can be ID'd by the pale appearance compared to the good connectors.
you cannot get new TEK ribbon cable assys anymore.

for 7600s that use spec analyzer modules,there was a mod that added a fan
on the back,a larger shield over the heat sink to accomodate the fan,and
changed a current limit resistor on one of the supplies.
(by paralleling another R across it)
(can't recall which,though...a current schematic should have it ID'd)

--
Jim Yanik
jyanik
at
kua.net

 

[Jorgen Lund-Nielsen]

GanjaTron wrote:

Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

Regards,

--Roland

You also have to check the ESR of the electrolytics with an ESR-Meter.
Often elytics have still their capacitance but the ESR goes up and than
they are nearly functionless.

Jorgen
dj0ud

 

[GanjaTron]

On Jun 19, 9:49 am, Jorgen Lund-Nielsen <jorgen.lund-
niel...@xyz123desy.de> wrote:

GanjaTron wrote:
Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

Regards,

--Roland

You also have  to check the ESR of the electrolytics with an ESR-Meter.
Often elytics have still their capacitance but the ESR goes up and than
they are nearly functionless.

Hmmm, even if I had an ESR tester at hand, I wouldn't have the
reference values. Is there a "sane" range for these big-ass caps?

--Roland

 

[Jim Yanik]

Jorgen Lund-Nielsen <jorgen.lund-nielsen@xyz123desy.de> wrote in
news:h1fftq$5gc$1@it-news01.desy.de:

GanjaTron wrote:
Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

Regards,

--Roland

You also have to check the ESR of the electrolytics with an ESR-Meter.
Often elytics have still their capacitance but the ESR goes up and than
they are nearly functionless.

Jorgen
dj0ud

on the 7600 scopes,I just checked the unreg voltages across the PS caps.
If it's low,I replaced the bad filter caps.
A scope will also tell you if the caps are bad.(ripple voltage)

--
Jim Yanik
jyanik
at
kua.net

 

[Jorgen Lund-Nielsen]

GanjaTron wrote:

On Jun 19, 9:49 am, Jorgen Lund-Nielsen <jorgen.lund-
niel...@xyz123desy.de> wrote:

GanjaTron wrote:

Well, I replaced the CA3046s with a pair of CA3086s. Triggers fine
now. Having said that, there's some noticeable noise (as in
flickering) in the trace. I checked the power supply caps with a
capacitance meter, and they look ok (so do the supply lines measured
with another scope). Any ideas what else I should check?

Regards,

--Roland

You also have to check the ESR of the electrolytics with an ESR-Meter.
Often elytics have still their capacitance but the ESR goes up and than
they are nearly functionless.


Hmmm, even if I had an ESR tester at hand, I wouldn't have the
reference values. Is there a "sane" range for these big-ass caps?

--Roland

Hi Roland,

the most ESR-Meters have a reference list printed on the housing
as you can see here on some pics:

http://www.electronicrepairguide.com/capanalyzer%20esr%20meter.jpg

http://www.nippur.hu/esr_meter_nagy.jpg

http://www.electronicrepairguide.com/esr%20capacitor%20tester.jpg

Jorgen
dj0ud

 

[GanjaTron]

Thanks for all the replies! I did check for ripple with a working
scope, and found a few lines with obvious sine waves (like 4Vpp), but
I understand the PS also has unregulated outputs, so I didn't
investigate any further. The cap voltages themselves checked OK with a
voltmeter.

Jeff, when you say the caps "blow", you mean they literally
explode? :^O

The caps on the interface board would be the next suspects, if they
weren't so tough to get at (on top of which I'd have to lift them out
at one end to check).

This particular 7603 has the fan mod, btw. The TO-3s show no signs of
cracks, and I didn't find the gold dot connectors you mentioned. I
guess this is a revision. Mainframe serial# is B377720 with option 03,
which according to the service manual means EMI shielding, though I
can't find the bits mentioned there. Oh, and it has the readout. Trace
is mushy and the scope stinks. ;^)

Regards,

--Roland

 

[Jeff Liebermann]

On Mon, 22 Jun 2009 05:08:14 -0700 (PDT), GanjaTron
<ganjatron@gmx.net> wrote:

Thanks for all the replies! I did check for ripple with a working
scope, and found a few lines with obvious sine waves (like 4Vpp), but
I understand the PS also has unregulated outputs, so I didn't
investigate any further. The cap voltages themselves checked OK with a
voltmeter.

If the caps are bad, the voltage will be temporarily within limits,
but the ripple voltage will be rather high. That causes blurred
traces that can't be adjusted out with the focus and astigmatism
controls. Use another scope to verify that you're getting DC on the
PS voltages.

Jeff, when you say the caps "blow", you mean they literally
explode? :^O

No. They got hot and eventually blew a series resistor or fuse. I
forgot which. I got lucky and caught it before it destroyed any
active components. The bakelite bottom of the can capacitors were
obviously bulging and had turned from brown to black. My capacitance
and ESR capacitor tester both showed that they were under value and
with a very high internal series resistance.

I won't mention what I used to replace the caps, or how the
replacements were installed. I'm not very proud of the work.

The caps on the interface board would be the next suspects, if they
weren't so tough to get at (on top of which I'd have to lift them out
at one end to check).

If it were easy, it would be no fun. If you don't want to do it
twice, just find the replacement caps and install them instead of
testing the originals. This way you're sure that you won't need to
dive in again later.

This particular 7603 has the fan mod, btw. The TO-3s show no signs of
cracks, and I didn't find the gold dot connectors you mentioned. I
guess this is a revision. Mainframe serial# is B377720 with option 03,
which according to the service manual means EMI shielding, though I
can't find the bits mentioned there. Oh, and it has the readout. Trace
is mushy and the scope stinks. ;^)

The stink is a clue. It's probably boiled electrolyte.

Regards,

--Roland
--

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

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:ucav359o35ql0mujoua9qk1lapdlj9i9fb@4ax.com:

On Mon, 22 Jun 2009 05:08:14 -0700 (PDT), GanjaTron
ganjatron@gmx.net> wrote:

Thanks for all the replies! I did check for ripple with a working
scope, and found a few lines with obvious sine waves (like 4Vpp), but
I understand the PS also has unregulated outputs, so I didn't
investigate any further. The cap voltages themselves checked OK with a
voltmeter.

If the caps are bad, the voltage will be temporarily within limits,
but the ripple voltage will be rather high. That causes blurred
traces that can't be adjusted out with the focus and astigmatism
controls. Use another scope to verify that you're getting DC on the
PS voltages.

Jeff, when you say the caps "blow", you mean they literally
explode? :^O

No. They got hot and eventually blew a series resistor or fuse. I
forgot which. I got lucky and caught it before it destroyed any
active components. The bakelite bottom of the can capacitors were
obviously bulging and had turned from brown to black. My capacitance
and ESR capacitor tester both showed that they were under value and
with a very high internal series resistance.

I've seen 7600 filter caps leak electrolyte,all over the cap/rectifier
board.

I won't mention what I used to replace the caps, or how the
replacements were installed. I'm not very proud of the work.

Well,if you can't get direct replacements,then you go with the next best
sub. ;-)

I've seen all sorts of customer "repairs".

The caps on the interface board would be the next suspects, if they
weren't so tough to get at (on top of which I'd have to lift them out
at one end to check).

If it were easy, it would be no fun. If you don't want to do it
twice, just find the replacement caps and install them instead of
testing the originals. This way you're sure that you won't need to
dive in again later.

This particular 7603 has the fan mod, btw. The TO-3s show no signs of
cracks,
and I didn't find the gold dot connectors you mentioned. I
guess this is a revision. Mainframe serial# is B377720 with option 03,
which according to the service manual means EMI shielding, though I
can't find the bits mentioned there. Oh, and it has the readout. Trace
is mushy and the scope stinks. ;^)

The stink is a clue. It's probably boiled electrolyte.

Regards,

--Roland

FYI,you can tell the approx. manufacturing date by checking date codes on
several components,like filter caps,power xfmr,and ICs.
8644 would be 1986,week 44

I'd say your 7603 is a fairly "new" one,that's a high serial number.


--
Jim Yanik
jyanik
at
kua.net

 

[GanjaTron]

On Jun 22, 6:23 pm, Jim Yanik <jya...@abuse.gov> wrote:

Jeff Liebermann <je...@cruzio.com> wrote innews:ucav359o35ql0mujoua9qk1lapdlj9i9fb@4ax.com:

FYI,you can tell the approx. manufacturing date by checking date codes on
several components,like filter caps,power xfmr,and ICs.  
8644 would be 1986,week 44

I'd say your7603is a fairly "new" one,that's a high serial number.

Well, I see what *could* be date codes like 8352 and 8413 on a few
trannies, and 8439L on a PS cap. I can't believe they built these
clunkers well into the mid-80s! Everything about this scope screams
70s!

The stink is more like stale cigarette smoke, which is a lot worse
than electrolyte. I know electrolyte when I smell it.

PS cap replacement is a challenge given the fact none of the readily
available replacements I found have matching pin configurations (plus
is usually centered rather than offset to one side). Sprague
apparently had their own system, and bending pins is not an option
here.

Regards,

--Roland

 

[GanjaTron]

Oh, mine says "inspected by Jerry". I guess Tom had the day off. :^D

--Roland