Tek 7603 Followed Me Home


bobh@joba.com
 

I have seen this Tek 7603 scope sitting on the table at the Tek Country store for at least three years.  I have tried to power it up and twist some knobs several times over the years with no response.  They have been asking $35 for it and I noticed today there are about 5-6 price stickers stacked up under the current one.

I have been thinking a 7603 would fit into my ensemble if I clear space for it by giving another scope to the Tek Museum.   So, I asked if they would take $25 for it and they did.  So, here it sits with the covers off and the power supply hanging out the back.  It doesn't do nut-tin when powered up.

The main fuse, the fuse on the regulator board and the one on the power supply board above the caps are good. I checked the power supply voltages on the regulator board with the following results:

Volt        VDC      VAC
130       114          11
50            44           5
5            4.396       0.25
15           13.2        1.4
-15         -13.17      1.3
-50          -44          4.8

Unregulated Voltages

50           66            0.16
-50        -52              13
15           24              0.04
-15       -24               0.1
5           12.4             0.05

Seems to be discrepancies between the ripple on the corresponding regulated and unregulated supplies which I don't understand.

The 130 volt supply is partly made up from the 50 volt supply and the voltage on the emitter of Q850 should add about 40 volts but I measure 10.8 volts DC there.  Maybe I see it now, if the 50v supply is at 44 volts there is no way the emitter of Q850 can get to 40 v.

I appreciate any ideas from folks especially those who have been thru a 7603 before.  Haven't had a chance to research the archive but will do that before doing more troubleshooting.  I can't take another scope to the Tek Museum until I know we can bring this one back to service.

Bob.


Chuck Harris <cfharris@...>
 

What plugins do you have installed?

Without plugins, you might get the green power lamp to
light... assuming it isn't burned out.

-Chuck Harris

Robert Hay wrote:

I have seen this Tek 7603 scope sitting on the table at the Tek Country store for at
least three years. I have tried to power it up and twist some knobs several times
over the years with no response. They have been asking $35 for it and I noticed
today there are about 5-6 price stickers stacked up under the current one.

I have been thinking a 7603 would fit into my ensemble if I clear space for it by
giving another scope to the Tek Museum. So, I asked if they would take $25 for it
and they did. So, here it sits with the covers off and the power supply hanging out
the back. It doesn't do nut-tin when powered up.

The main fuse, the fuse on the regulator board and the one on the power supply board
above the caps are good. I checked the power supply voltages on the regulator board
with the following results:

Volt VDC VAC
130 114 11
50 44 5
5 4.396 0.25
15 13.2 1.4
-15 -13.17 1.3
-50 -44 4.8

Unregulated Voltages

50 66 0.16
-50 -52 13
15 24 0.04
-15 -24 0.1
5 12.4 0.05

Seems to be discrepancies between the ripple on the corresponding regulated and
unregulated supplies which I don't understand.

The 130 volt supply is partly made up from the 50 volt supply and the voltage on the
emitter of Q850 should add about 40 volts but I measure 10.8 volts DC there. Maybe I
see it now, if the 50v supply is at 44 volts there is no way the emitter of Q850 can
get to 40 v.

I appreciate any ideas from folks especially those who have been thru a 7603 before.
Haven't had a chance to research the archive but will do that before doing more
troubleshooting. I can't take another scope to the Tek Museum until I know we can
bring this one back to service.

Bob.







bobh@joba.com
 

So far no plugins and the light isn't lit.  I'll check it.

Bob.

On 9/8/2018 7:43 PM, Robert Hay wrote:
I have seen this Tek 7603 scope sitting on the table at the Tek Country store for at least three years.  I have tried to power it up and twist some knobs several times over the years with no response.  They have been asking $35 for it and I noticed today there are about 5-6 price stickers stacked up under the current one.

I have been thinking a 7603 would fit into my ensemble if I clear space for it by giving another scope to the Tek Museum.   So, I asked if they would take $25 for it and they did.  So, here it sits with the covers off and the power supply hanging out the back.  It doesn't do nut-tin when powered up.

The main fuse, the fuse on the regulator board and the one on the power supply board above the caps are good. I checked the power supply voltages on the regulator board with the following results:

Volt        VDC      VAC
130       114          11
50            44           5
5            4.396       0.25
15           13.2        1.4
-15         -13.17      1.3
-50          -44          4.8

Unregulated Voltages

50           66            0.16
-50        -52              13
15           24              0.04
-15       -24               0.1
5           12.4             0.05

Seems to be discrepancies between the ripple on the corresponding regulated and unregulated supplies which I don't understand.

The 130 volt supply is partly made up from the 50 volt supply and the voltage on the emitter of Q850 should add about 40 volts but I measure 10.8 volts DC there.  Maybe I see it now, if the 50v supply is at 44 volts there is no way the emitter of Q850 can get to 40 v.

I appreciate any ideas from folks especially those who have been thru a 7603 before.  Haven't had a chance to research the archive but will do that before doing more troubleshooting.  I can't take another scope to the Tek Museum until I know we can bring this one back to service.

Bob.






Dave Daniel
 

This is obvious, but make sure that the fuse is installed and of the correct rating.

DaveD

On 9/9/2018 9:22 AM, Robert Hay wrote:
So far no plugins and the light isn't lit.  I'll check it.

Bob.


On 9/8/2018 7:43 PM, Robert Hay wrote:
I have seen this Tek 7603 scope sitting on the table at the Tek Country store for at least three years.  I have tried to power it up and twist some knobs several times over the years with no response.  They have been asking $35 for it and I noticed today there are about 5-6 price stickers stacked up under the current one.

I have been thinking a 7603 would fit into my ensemble if I clear space for it by giving another scope to the Tek Museum. So, I asked if they would take $25 for it and they did.  So, here it sits with the covers off and the power supply hanging out the back.  It doesn't do nut-tin when powered up.

The main fuse, the fuse on the regulator board and the one on the power supply board above the caps are good. I checked the power supply voltages on the regulator board with the following results:

Volt        VDC      VAC
130       114          11
50            44           5
5            4.396       0.25
15           13.2        1.4
-15         -13.17      1.3
-50          -44          4.8

Unregulated Voltages

50           66            0.16
-50        -52              13
15           24              0.04
-15       -24               0.1
5           12.4             0.05

Seems to be discrepancies between the ripple on the corresponding regulated and unregulated supplies which I don't understand.

The 130 volt supply is partly made up from the 50 volt supply and the voltage on the emitter of Q850 should add about 40 volts but I measure 10.8 volts DC there.  Maybe I see it now, if the 50v supply is at 44 volts there is no way the emitter of Q850 can get to 40 v.

I appreciate any ideas from folks especially those who have been thru a 7603 before.  Haven't had a chance to research the archive but will do that before doing more troubleshooting.  I can't take another scope to the Tek Museum until I know we can bring this one back to service.

Bob.







Chuck Harris <cfharris@...>
 

No plugins, and the scope will do nothing.
The little green lights burn out all of the
time.

The manual tells you everything you need to
know about power supply diagnosis. It is
expecting that you will make DC measurements
with a DVM, and ripple measurements with another
scope, set to LINE trigger, and sweep at 5ms/div.

In this mode, ripple will be stationary.

The really high frequency glitches on the power
can be ignored, but the 60Hz and 120Hz ripple
are important, as are the general noise level.

The unregulated outputs are not critical as
to value, but do need to be close. They are
not especially critical as to ripple, expect
high values. Their purpose is to feed regulators.

They will vary greatly depending on your mains
voltage, and the mains setting of the scope.

The 7603 has a linear power supply. All of the
regulators are referenced to the -50V regulated
supply. You show it way off, everything else will
be off proportionately. Fix it first. Don't just
adjust it, fix it.

-Chuck Harris

Robert Hay wrote:

So far no plugins and the light isn't lit. I'll check it.

Bob.


On 9/8/2018 7:43 PM, Robert Hay wrote:
I have seen this Tek 7603 scope sitting on the table at the Tek Country store for
at least three years. I have tried to power it up and twist some knobs several
times over the years with no response. They have been asking $35 for it and I
noticed today there are about 5-6 price stickers stacked up under the current one.

I have been thinking a 7603 would fit into my ensemble if I clear space for it by
giving another scope to the Tek Museum. So, I asked if they would take $25 for it
and they did. So, here it sits with the covers off and the power supply hanging
out the back. It doesn't do nut-tin when powered up.

The main fuse, the fuse on the regulator board and the one on the power supply
board above the caps are good. I checked the power supply voltages on the regulator
board with the following results:

Volt VDC VAC
130 114 11
50 44 5
5 4.396 0.25
15 13.2 1.4
-15 -13.17 1.3
-50 -44 4.8

Unregulated Voltages

50 66 0.16
-50 -52 13
15 24 0.04
-15 -24 0.1
5 12.4 0.05

Seems to be discrepancies between the ripple on the corresponding regulated and
unregulated supplies which I don't understand.

The 130 volt supply is partly made up from the 50 volt supply and the voltage on
the emitter of Q850 should add about 40 volts but I measure 10.8 volts DC there.
Maybe I see it now, if the 50v supply is at 44 volts there is no way the emitter of
Q850 can get to 40 v.

I appreciate any ideas from folks especially those who have been thru a 7603
before. Haven't had a chance to research the archive but will do that before doing
more troubleshooting. I can't take another scope to the Tek Museum until I know we
can bring this one back to service.

Bob.









bobh@joba.com
 

Chuck & Dave,

The fuses are good.  The jumper for 120/240 is there but not connected on one end.  I think this is correct since the three position plug seems to also parallel the windings for 120v.

I had tried a 7A22 & a 7B50 but the 7B50 is probably bad so I replaced it with a 7B53A and I now have some lights on the plug-ins and graticle light.  No trace, but moving the trigger knob does cause the trigger light to flicker as expected.

I can't work on it again until this evening.  I'll re-check the voltages and check the ripple(s) with another scope.

Bob.

On 9/9/2018 7:36 AM, Chuck Harris wrote:
No plugins, and the scope will do nothing.
The little green lights burn out all of the
time.

The manual tells you everything you need to
know about power supply diagnosis. It is
expecting that you will make DC measurements
with a DVM, and ripple measurements with another
scope, set to LINE trigger, and sweep at 5ms/div.

In this mode, ripple will be stationary.

The really high frequency glitches on the power
can be ignored, but the 60Hz and 120Hz ripple
are important, as are the general noise level.

The unregulated outputs are not critical as
to value, but do need to be close. They are
not especially critical as to ripple, expect
high values. Their purpose is to feed regulators.

They will vary greatly depending on your mains
voltage, and the mains setting of the scope.

The 7603 has a linear power supply. All of the
regulators are referenced to the -50V regulated
supply. You show it way off, everything else will
be off proportionately. Fix it first. Don't just
adjust it, fix it.

-Chuck Harris

Robert Hay wrote:
So far no plugins and the light isn't lit. I'll check it.

Bob.


On 9/8/2018 7:43 PM, Robert Hay wrote:
I have seen this Tek 7603 scope sitting on the table at the Tek Country store for
at least three years. I have tried to power it up and twist some knobs several
times over the years with no response. They have been asking $35 for it and I
noticed today there are about 5-6 price stickers stacked up under the current one.

I have been thinking a 7603 would fit into my ensemble if I clear space for it by
giving another scope to the Tek Museum. So, I asked if they would take $25 for it
and they did. So, here it sits with the covers off and the power supply hanging
out the back. It doesn't do nut-tin when powered up.

The main fuse, the fuse on the regulator board and the one on the power supply
board above the caps are good. I checked the power supply voltages on the regulator
board with the following results:

Volt VDC VAC
130 114 11
50 44 5
5 4.396 0.25
15 13.2 1.4
-15 -13.17 1.3
-50 -44 4.8

Unregulated Voltages

50 66 0.16
-50 -52 13
15 24 0.04
-15 -24 0.1
5 12.4 0.05

Seems to be discrepancies between the ripple on the corresponding regulated and
unregulated supplies which I don't understand.

The 130 volt supply is partly made up from the 50 volt supply and the voltage on
the emitter of Q850 should add about 40 volts but I measure 10.8 volts DC there.
Maybe I see it now, if the 50v supply is at 44 volts there is no way the emitter of
Q850 can get to 40 v.

I appreciate any ideas from folks especially those who have been thru a 7603
before. Haven't had a chance to research the archive but will do that before doing
more troubleshooting. I can't take another scope to the Tek Museum until I know we
can bring this one back to service.

Bob.








John Griessen
 

On 9/9/18 10:11 AM, Robert Hay wrote:
I'll re-check the voltages
50 and -50 being actual 44 and -44 is the big clue.

Chuck was saying you probably have a very much changed component contributing
the the +44 and -44 regulated voltages, so some individual component volt level measurements are next to do.

Them both being the same 44V suggests some protection feature of the circuit is kicking in because some
filter caps are too leaky, but not shorted or open yet.
Look for bad caps there after the regulator.

The -52 for unregulated 50 is not likely enough headroom to regulate to 50V, so that is suspect also.
Look for bad caps there before the regulator.


Chuck Harris <cfharris@...>
 

My guess would be the -50V unregulated supply's
filter capacitor is no longer any good.

His VAC readings are certainly Vrms as read by his
DVM, so they are 2 x 1.4Vp-p, or in other words, he
has: 13Vrms x 2.8Vp-p/Vrms, or 36Vp-p ripple on a 50V
unregulated supply. No way that can work!

-Chuck Harris

John Griessen wrote:

On 9/9/18 10:11 AM, Robert Hay wrote:
I'll re-check the voltages
50 and -50 being actual 44 and -44 is the big clue.

Chuck was saying you probably have a very much changed component contributing
the the +44 and -44 regulated voltages, so some individual component volt level
measurements are next to do.

Them both being the same 44V suggests some protection feature of the circuit is
kicking in because some
filter caps are too leaky, but not shorted or open yet.
Look for bad caps there after the regulator.

The -52 for unregulated 50 is not likely enough headroom to regulate to 50V, so that
is suspect also.
Look for bad caps there before the regulator.




John Griessen
 

On 9/9/18 11:57 AM, Chuck Harris wrote:
His VAC readings are certainly Vrms as read by his
DVM, so they are 2 x 1.4Vp-p, or in other words, he
has: 13Vrms x 2.8Vp-p/Vrms, or 36Vp-p ripple on a 50V
unregulated supply. No way that can work!
Oh, yeah, missed that DVM VAC reading. Must be a little air capacitance in a dried out can!
Really suggests caps needing replacing.


bobh@joba.com
 

Yup, DMM916 meter readings.  My day was spent taking out of town guests up the Columbia Gorge.  Will try to dig further into it tomorrow.  Seems like the load from the plugins help stabilize some of the voltages but the -50 is not right.

Bob.

On 9/9/2018 9:57 AM, Chuck Harris wrote:
My guess would be the -50V unregulated supply's
filter capacitor is no longer any good.

His VAC readings are certainly Vrms as read by his
DVM, so they are 2 x 1.4Vp-p, or in other words, he
has: 13Vrms x 2.8Vp-p/Vrms, or 36Vp-p ripple on a 50V
unregulated supply. No way that can work!

-Chuck Harris

John Griessen wrote:
On 9/9/18 10:11 AM, Robert Hay wrote:
I'll re-check the voltages
50 and -50 being actual 44 and -44 is the big clue.

Chuck was saying you probably have a very much changed component contributing
the the +44 and -44 regulated voltages, so some individual component volt level
measurements are next to do.

Them both being the same 44V suggests some protection feature of the circuit is
kicking in because some
filter caps are too leaky, but not shorted or open yet.
Look for bad caps there after the regulator.

The -52 for unregulated 50 is not likely enough headroom to regulate to 50V, so that
is suspect also.
Look for bad caps there before the regulator.




bobh@joba.com
 

Chuck,

C808 on the -50 v unregulated is the only cap that tests at 0.0 Ohms and is the only one that doesn't charge up to some value using the cap test position on my Tek DMM916.

I ordered some replacement caps although I am not sure whether to ultimately replace all the cans in the back section.  I may use two 1000ufd 100v caps to replace the 1800 ufd 75 volt C808 on the -50 unreg.  In this case the can is connected to the -50 unregulated rather than ground so I need to tie all those loose ends together.

I'll hit up the local electronic surplus tomorrow to see if I can find a replacement cap for testing while waiting for the ones I ordered.

Bob.

On 9/9/2018 9:57 AM, Chuck Harris wrote:
My guess would be the -50V unregulated supply's
filter capacitor is no longer any good.

His VAC readings are certainly Vrms as read by his
DVM, so they are 2 x 1.4Vp-p, or in other words, he
has: 13Vrms x 2.8Vp-p/Vrms, or 36Vp-p ripple on a 50V
unregulated supply. No way that can work!

-Chuck Harris

John Griessen wrote:
On 9/9/18 10:11 AM, Robert Hay wrote:
I'll re-check the voltages
50 and -50 being actual 44 and -44 is the big clue.

Chuck was saying you probably have a very much changed component contributing
the the +44 and -44 regulated voltages, so some individual component volt level
measurements are next to do.

Them both being the same 44V suggests some protection feature of the circuit is
kicking in because some
filter caps are too leaky, but not shorted or open yet.
Look for bad caps there after the regulator.

The -52 for unregulated 50 is not likely enough headroom to regulate to 50V, so that
is suspect also.
Look for bad caps there before the regulator.




Chuck Harris <cfharris@...>
 

I am not sure what you are saying when you say that
C808 tests at 0.0 ohms. Do you perhaps mean 0.0 uf?

Typically, when ripple gets to be that excessive, the
capacitor's internal connection has been etched away
and is open circuit, or the capacitor's electrolyte
has dried up. The capacitance goes to near zero uf.

As a temporary fix, you can get back in business by
paralleling just about anything across the original
capacitor at its terminals. Even as little as 1/10th
the correct value will sometimes be close for the circuitry
to limp along and work. Tektronix was very generous
with its margins.

-Chuck Harris

Robert Hay wrote:

Chuck,

C808 on the -50 v unregulated is the only cap that tests at 0.0 Ohms and is the only
one that doesn't charge up to some value using the cap test position on my Tek DMM916.

I ordered some replacement caps although I am not sure whether to ultimately replace
all the cans in the back section. I may use two 1000ufd 100v caps to replace the
1800 ufd 75 volt C808 on the -50 unreg. In this case the can is connected to the -50
unregulated rather than ground so I need to tie all those loose ends together.

I'll hit up the local electronic surplus tomorrow to see if I can find a replacement
cap for testing while waiting for the ones I ordered.

Bob.

On 9/9/2018 9:57 AM, Chuck Harris wrote:
My guess would be the -50V unregulated supply's
filter capacitor is no longer any good.


Kevin Wood G7BCS
 

If it helps, I had a 7603 fault due to one of those reservoir caps failing
and, when I got round to checking them, most of the caps on that rectifier
board were on their way out, so I changed them all.

That doesn't mean yours will be, of course, and I'm not generally an
advocate of "re-capping" devices en-masse, but my recollection is that it
was not that easy to get to the board and change the caps either, so it
might be a false economy to change just one or two.

Beware that several of those caps have multiple can connections to the
board and, on some, I think they are used as "jumpers" to connect traces
across the board. If replacing with caps of a different form factor, which
will probably be almost inevitable, you might need to insert jumpers
across some of the can connections. Apologies if I'm delivering lessons in
"egg-sucking"!

Kevin
G7BCS

Chuck,

C808 on the -50 v unregulated is the only cap that tests at 0.0 Ohms and
is the only one that doesn't charge up to some value using the cap test
position on my Tek DMM916.

I ordered some replacement caps although I am not sure whether to
ultimately replace all the cans in the back section.  I may use two
1000ufd 100v caps to replace the 1800 ufd 75 volt C808 on the -50
unreg.  In this case the can is connected to the -50 unregulated rather
than ground so I need to tie all those loose ends together.

I'll hit up the local electronic surplus tomorrow to see if I can find a
replacement cap for testing while waiting for the ones I ordered.

Bob.


tom jobe <tomjobe@...>
 

Hi Chuck,
I think he means it appears to have a dead short (or close to it) and this is why I say that:
I have been following this 7603 thread, and had printed the power supply schematic out on large size paper to study as I followed this interesting thread.
Yesterday I thought my interest in this 7603 thread might also be a good excuse to try to fix a 7603 I have that has a large note on it about blowing the fuse instantly when it gets powered on.
There did not appear to be any short on the primary side of the main transformer, so soon this 7603's power supply was out and apart so I could check the large filter capacitors for ESR and resistance in the circuit. C808 appeared to be a full short in circuit to an ESR meter and to an ordinary Fluke DMM.
A study of the circuitry around C808 shows several other paths a short circuit could come from with everything still in the circuit, and that is where I left my search yesterday.
I figured I would study the power supply schematic and see what else I could figure out before removing any of the possible problem components.
This morning I was quite surprised to see Robert's report of finding a shorted C808 in his 7603!
Then when I saw Chuck's question this morning... I realized that my thinking there could even be a dead short in an aluminum electrolytic cap might need to be re-thought.
Other details:
This capacitor is part of the filtering of the 50 VDC supply immediately after the full wave rectifier. This transformer winding is center tapped to ground and two capacitors are used on the plus and minus outputs of the rectifier to ground. This C808 is on the negative side to ground, and a C909 on the positive side to ground. These two capacitors are identical (1800 uF/75 v) and C909 does not appear to be shorted when tested in circuit (several thousand ohms) which left me 'scratching my head' at the end of yesterday's investigation.
tom jobe...

On 9/11/2018 5:15 AM, Chuck Harris wrote:
I am not sure what you are saying when you say that
C808 tests at 0.0 ohms. Do you perhaps mean 0.0 uf?

Typically, when ripple gets to be that excessive, the
capacitor's internal connection has been etched away
and is open circuit, or the capacitor's electrolyte
has dried up. The capacitance goes to near zero uf.

As a temporary fix, you can get back in business by
paralleling just about anything across the original
capacitor at its terminals. Even as little as 1/10th
the correct value will sometimes be close for the circuitry
to limp along and work. Tektronix was very generous
with its margins.

-Chuck Harris

Robert Hay wrote:
Chuck,

C808 on the -50 v unregulated is the only cap that tests at 0.0 Ohms and is the only
one that doesn't charge up to some value using the cap test position on my Tek DMM916.

I ordered some replacement caps although I am not sure whether to ultimately replace
all the cans in the back section. I may use two 1000ufd 100v caps to replace the
1800 ufd 75 volt C808 on the -50 unreg. In this case the can is connected to the -50
unregulated rather than ground so I need to tie all those loose ends together.

I'll hit up the local electronic surplus tomorrow to see if I can find a replacement
cap for testing while waiting for the ones I ordered.

Bob.

On 9/9/2018 9:57 AM, Chuck Harris wrote:
My guess would be the -50V unregulated supply's
filter capacitor is no longer any good.


Chuck Harris <cfharris@...>
 

That wouldn't explain why he reports the voltage across C808 is about
-52V with about 30Vp-p ripple.

I think he meant 0.0uf... and the rest of my post was with that thought
in mind.

-Chuck Harris

tom jobe wrote:

Hi Chuck,
I think he means it appears to have a dead short (or close to it) and this is why I
say that:
I have been following this 7603 thread, and had printed the power supply schematic
out on large size paper to study as I followed this interesting thread.
Yesterday I thought my interest in this 7603 thread might also be a good excuse to
try to fix a 7603 I have that has a large note on it about blowing the fuse


tom jobe <tomjobe@...>
 

Thanks Chuck,
Whoops... I do remember him saying he had the -52 volts, another little detail that sailed right over my head!
It must be those damn birthdays that keep flying by, the 78th just went by.
tom jobe...

On 9/11/2018 8:11 AM, Chuck Harris wrote:
That wouldn't explain why he reports the voltage across C808 is about
-52V with about 30Vp-p ripple.

I think he meant 0.0uf... and the rest of my post was with that thought
in mind.

-Chuck Harris

tom jobe wrote:
Hi Chuck,
I think he means it appears to have a dead short (or close to it) and this is why I
say that:
I have been following this 7603 thread, and had printed the power supply schematic
out on large size paper to study as I followed this interesting thread.
Yesterday I thought my interest in this 7603 thread might also be a good excuse to
try to fix a 7603 I have that has a large note on it about blowing the fuse


bobh@joba.com
 

Chuck & Tom,

I just rechecked the unreg. -15v Ohms across C808 and I think I just screwed up on that measurement.  The + side of the cap is grounded and I think I must have just measured from ground to ground.  Now I get about 7k Ohms from can case (-) to ground. And, my $10 component identifier says it's a diode which makes sense because of the rectifier circuit through that sec winding.

And Kevin, thanks for your ideas.  I was aware that the four can connections make up parts of the circuit and I will probably needed jumpers.  But, I need all the help and ideas to stay on course.

Thanks guys,

Bob.

On 9/11/2018 8:27 AM, tom jobe wrote:
Thanks Chuck,
Whoops... I do remember him saying he had the -52 volts, another little detail that sailed right over my head!
It must be those damn birthdays that keep flying by, the 78th just went by.
tom jobe...

On 9/11/2018 8:11 AM, Chuck Harris wrote:
That wouldn't explain why he reports the voltage across C808 is about
-52V with about 30Vp-p ripple.

I think he meant 0.0uf... and the rest of my post was with that thought
in mind.

-Chuck Harris

tom jobe wrote:
Hi Chuck,
I think he means it appears to have a dead short (or close to it) and this is why I
say that:
I have been following this 7603 thread, and had printed the power supply schematic
out on large size paper to study as I followed this interesting thread.
Yesterday I thought my interest in this 7603 thread might also be a good excuse to
try to fix a 7603 I have that has a large note on it about blowing the fuse



John Griessen
 

On 9/11/18 11:01 AM, Robert Hay wrote:
Chuck & Tom,
I just rechecked the unreg. -15v Ohms across C808 and

The mismatch of the units stops this from being helpful.
Can you tell us what you mean about unreg ohms of a capacitor? Or correct the mistake?

Do you mean volts across c808?

It's gotta match up to give an answer that means anything or helps anything.


bobh@joba.com
 

Hmm, poor reporting on my part.

 I measured the _Ohms_ across C808, which is on the (damn not -15) -50 volt unregulated, and it measures about 7k Ohms.  This was to correct my previous email saying I had measured 0.0 Ohms.

Bob.

On 9/11/2018 9:27 AM, John Griessen wrote:
On 9/11/18 11:01 AM, Robert Hay wrote:
Chuck & Tom,

I just rechecked the unreg. -15v Ohms across C808 and

The mismatch of the units stops this from being helpful.
Can you tell us what you mean about unreg ohms of a capacitor?  Or correct the mistake?

Do you mean volts across c808?

It's gotta match up to give an answer that means anything or helps anything.



Chuck Harris <cfharris@...>
 

There is very little value in measuring the resistance
across these filter capacitors.

The ripple measurements tell the tale. If you had a scope
to use to look at the voltage across that capacitor, you
would see the unambiguous sign of a bad capacitor..

Replace the capacitor and move on.

-Chuck Harris

Robert Hay wrote:

Hmm, poor reporting on my part.

I measured the _Ohms_ across C808, which is on the (damn not -15) -50 volt
unregulated, and it measures about 7k Ohms. This was to correct my previous email
saying I had measured 0.0 Ohms.

Bob.