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Hi, my name is Jim and I'm a Tek-aholic. ("Hi, Jim.") Long time lurker (about a year and a half), first time poster. My latest Tek project is a completely dead 7603 that I bought on the 'Bay. I did get a working 7S11 sampling plug-in and a 7A26 and a 7A18 in mostly working condition in the deal. Anyway, the 7603, serial number B345179, shows no signs of life whatsoever. No lights light, no sounds, no nothing when I pull the on/off switch out. I checked the main fuse, the thermal cutout, and the on/off switch. No issues there, 120 VAC gets through all of those. I'm wondering if the main transformer is blown. Sounds expensive. I'm not retired, like some of you are (God bless you!), so I unfortunately don't have a lot of time on my hands. Got a working 7904 and a 5103N/D10 to help troubleshoot, plus half a dozen odd multimeters in my garage lab. (Also, a fair number of 7000 series plug-ins, a Tek TLA711 logic analyzer [I'll do a post on that one someday], a good collection of HP microwave gear, and some other manufacturers' stuff).

Yes, I have the service manual for the 7603, but I haven't been able to decipher where the main xfmr secondary test points are located, if there are any. Any guidance, folks? I'm continually in awe of the man-years (and some woman-years, too) of collective experience concentrated in this place called TekScopes!

Thanks! Jim

That model, if the graticule lights work you got juice to the Xfmr. Other lights are a different story. If you get absolutely nothing, turn it on and see if the blades of the power plug read infinity between. If so it is either the primary of the transformer or a thermal in it, or maybe something to do with the voltage selection. You DO have the voltage selector in properly right ?

It is rare for a primary of a power transformer to open up. But on any given Tuesday a connection could be defective and it didn't show up. If you get an open reading find the actual primary and measure it. Maybe stick 120 VAC in it through a 100 watt incandescent.

If your main low voltage supplies are all there you should check for HV, and it is not like that requires a HV probe, there are places to measure where you can tell. The cathode voltage is only about 3KV, so even if it goes overload on a DVM that can handle 2KV it shouldn't hurt it. if it has HV then go to the deflection plate voltages, just because it is easy. The ones on the top should be within a few volts of each other, same with the side ones.

After that you might need to go to the CRT grids.

Whatever, if it does absolutely noting that is usually a good omen. If it is just something stopping the 120 VAC from getting to the iron, that is easy. (unless you need the transformer, but sometimes it is a thermal cutout and that can be replaced. Usually.

Keep us posted.

If your main low voltage supplies are all there you should check for HV, and it is not like that
requires a
HV probe, there are places to measure where you can tell. The cathode voltage is only about 3KV, so
even if it goes overload on a DVM that can handle 2KV it shouldn't hurt it. if it has HV then go to
the
deflection plate voltages, just because it is easy. The ones on the top should be within a few volts
of
each other, same with the side ones.

That diagnosis gives no information regarding the location of any HV fault. If the -3kV is not
present, the fault could either be the HV transformer, something in the string of components
associated with pin 8 of the transformer, or that the multiplier is dead and loading down the
transformer.

The HV multiplier (x4) is a known weak point. The good news is that you can rebuild it, if that is
where the fault lies.

Craig

Does it make a ticking sound - like 1/sec? You may need to put your ear
close to the cover to hear it. If so, it's something in the PSU - rectifier
board, LV board, inverter - likely a shorted tantalum cap.

You've got a dead 7603 with no lights. Definitely look at the low voltages first. Check the 0.15A (150mA) fuse, F855, just because its 'filament' is so delicate it can easily become disconnected from its end caps from heat and age. In my case this wasn't the 'magic bullet' to fixing my 7603, but losing the 130V line kills the HV system.

Getting the front panel power indicator to light would be the next challenge. The LV regulators are interconnected in a way that will prevent this lamp from lighting if one of them is bad. I can't remember how it all hangs together now, but there are a number of posts here that spell it out.

Sorry, about being too vague, but I'm writing this from memory. I think the LV rectifier board is going to be the key to this, and it's worth the time to pull it, give it a visual and check the condition of the electrolytic caps. And be sure to mark the ribbon cables as you disassemble things!

Good luck!

--Al

Does it make a ticking sound - like 1/sec? You may need to put your ear close to the cover to hear
it. If
so, it's something in the PSU - rectifier board, LV board, inverter - likely a shorted tantalum cap.

The 7603 uses a linear power supply, not a switcher. So no ticking.

Craig

On Mon, Jun 25, 2018 at 02:31 am, Craig Sawyers wrote:

That diagnosis gives no information regarding the location of any HV fault.

Yes, but we must know if there is a HV fault. Hope it's not the multiplier. But we do need to know if there is B+.

I figure the best way to proceed, once it is established that the low supplies are up, HV then plates and then grids. Agree ? If there is a short at the ultor supply the cathode end will balk at having too much voltage, neons, whatever else, maybe spark gaps. If there is a short on the cathode side there will be ultor voltage and a bit high, but it won't fry anything out and I am pretty sure it will not cause shutdown. Measuring the ultor voltage can be a real PITA, but it is not always necessary. For the cathode end, usually you can just add a 10 meg resistor in series with the probe which will double the range, just multiply the reading by 2. Many have 2 KV as the top range, so that works for actual measurement. If no resistor it just goes to overload and that tells you there is HV.

If you have a better procedure I would like to hear it. I am here to learn, just like anyone else.

If you have a better procedure I would like to hear it. I am here to learn, just like anyone else.

Turn the 7603 off, and then unplug the ht lead between the multiplier and the CRT (somewhat carefully!
You may have to undo the P clip that holds the plug/socket to the end of the HT chassis to get
access), and then short the exposed tip (which is at the end of the red lead that goes to the crt) to
metalwork. If there is a spark, then the CRT is receiving the output from the multiplier. If nothing
happens, suspect the multiplier. I have seen two 7603's - one a friends, and one mine, with dead
multipliers.

If you do get a healthy spark, then the HT transformer is OK (which means no shorted turns) and so is
the multiplier. Which means you look elsewhere for the fault.

Craig

Yep, set for 120 VAC.? I did move the jumper to Mid voltage.
I will try a night light in series as soon as I can.?
Thanks, Jeff


Sent from my Verizon, Samsung Galaxy smartphone

No, no ticking.? ?The scope loks and sounds exactly the same plugged in to the mains or not, power switch on or off.


Sent from my Verizon, Samsung Galaxy smartphone

I think I have a few low voltage supplies to check before getting to the HV stuff.
Thanks.


Sent from my Verizon, Samsung Galaxy smartphone

On Mon, Jun 25, 2018 at 07:45 pm, Jim Ford wrote:

then short the exposed tip (which is at the end of the red lead that goes to
the crt) to
metalwork. If there is a spark, then the CRT is receiving the output from the
multiplier

No. That is not proper procedure, this is not a lawn mower. You let that ultor voltage arc you are beating the shit out of a bunch of precision resistors in the chain for the CRT bias, stressing old unobtainium parts and once some of that shorts out you'll be sorry. If it is already shorted the voltage does not build up, if you make it so it can, the stress on the rest of it will be more severe as the capacitance discharges.

The arc method of testing is fine on an old "Madman Muntz", but not for Tek scopes.

So, sorry, I disagree.

On Mon, Jun 25, 2018 at 08:40 pm, Jeff Urban wrote:

On Mon, Jun 25, 2018 at 07:45 pm, Jim Ford wrote:

then short the exposed tip (which is at the end of the red lead that goes to
the crt) to
metalwork. If there is a spark, then the CRT is receiving the output from

the

multiplier

No. That is not proper procedure, this is not a lawn mower. You let that ultor
voltage arc you are beating the shit out of a bunch of precision resistors in
the chain for the CRT bias, stressing old unobtainium parts and once some of
that shorts out you'll be sorry. If it is already shorted the voltage does not
build up, if you make it so it can, the stress on the rest of it will be more
severe as the capacitance discharges.

The arc method of testing is fine on an old "Madman Muntz", but not for Tek
scopes.

So, sorry, I disagree.

I think that Jeff makes a good point here. There is no reason to test like that. You are very likely to burn up some good components through feedback, excess current or over-voltage. Causing any sort of high voltage supply to jump an arc requires a much higher voltage than is found in a normal circuit. For example, a car coil that may send 4-6kV across a good spark plug can be forced to produce 10 times as much voltage when made to jump a large gap, but they will not last long doing that. There are simply too many delicate parts in one of these scopes to use that method of testing.

--
Michael Lynch
Dardanelle, AR

On Mon, Jun 25, 2018 at 07:45 pm, Jim Ford wrote:


then short the exposed tip (which is at the end of the red lead that goes to
the crt) to
metalwork. If there is a spark, then the CRT is receiving the output from the
multiplier

No. That is not proper procedure, this is not a lawn mower. You let that ultor voltage arc you are beating the shit out of a bunch of precision resistors in the chain for the CRT bias, stressing old unobtainium parts and once some of that shorts out you'll be sorry. If it is already shorted the voltage does not build up, if you make it so it can, the stress on the rest of it will be more severe as the capacitance discharges.

The arc method of testing is fine on an old "Madman Muntz", but not for Tek scopes.

So, sorry, I disagree.


On Mon, Jun 25, 2018 at 09:08 pm, Mlynch001 wrote:

On Mon, Jun 25, 2018 at 08:40 pm, Jeff Urban wrote:

On Mon, Jun 25, 2018 at 07:45 pm, Jim Ford wrote:

then short the exposed tip (which is at the end of the red lead that goes

to

the crt) to
metalwork. If there is a spark, then the CRT is receiving the output from

the

multiplier

No. That is not proper procedure, this is not a lawn mower. You let that

ultor

voltage arc you are beating the shit out of a bunch of precision resistors

in

the chain for the CRT bias, stressing old unobtainium parts and once some of
that shorts out you'll be sorry. If it is already shorted the voltage does

not

build up, if you make it so it can, the stress on the rest of it will be

more

severe as the capacitance discharges.

The arc method of testing is fine on an old "Madman Muntz", but not for Tek
scopes.

So, sorry, I disagree.

I think that Jeff makes a good point here. There is no reason to test like
that. You are very likely to burn up some good components through feedback,
excess current or over-voltage. Causing any sort of high voltage supply to
jump an arc requires a much higher voltage than is found in a normal circuit.
For example, a car coil that may send 4-6kV across a good spark plug can be
forced to produce 10 times as much voltage when made to jump a large gap, but
they will not last long doing that. There are simply too many delicate parts
in one of these scopes to use that method of testing.

--
Michael Lynch
Dardanelle, AR

Ok. You can't just leave it there. How do you discharge the CRT? ?\_(ツ)_/?

Jeff, I have to disagree with your disagreement - when you short the PDA lead of a scope CRT to ground, you are (rapidly) discharging the filter capacitance of the internal carbon DAG or metallization to the outside coatings or surfaces like the (grounded) mu-shield. It is a common safety procedure to keep it safe during later work or CRT handling, and has nothing to do with the cathode circuit. There are risks though, like getting zapped yourself, or slipping during unplugging, letting the Alden connector tip accidentally hit circuitry instead of ground. It would be safer, but less exciting to discharge it in a less intense way via a high resistance, but when you only have two hands, each holding one end of a recently unplugged connector set, it's hard to add components to your situation. Direct shorting to ground is the most expedient method.

Sometimes the Aldens are tight after years of sitting, and are difficult to pull apart, then all of a sudden let loose easily. Before attempting disengagement, twist one end against the other to break the surface adhesion - especially if one part is silicone rubber, which tends to hang on tightly. Once the housings are free from each other, the main thing holding is the contacts. Then carefully apply the pulling force between the halves. When you feel it snap loose, you can slowly withdraw and expose the hot tip and touch it to the chassis.

I have done it plenty of times, and gotten zapped a bit approximately once, but it's harmless as long you're not surprised and lose control. My method nowadays is to wear leather work gloves, and grab the connector halves between the thumb and index finger of each hand, and levering between the thumb knuckles. The gloves soften up the forces on the thumbs, and help spread the arc if you happen to screw up. With practice, this can give very good control.

Now, TV CRTs are a different story - usually higher voltage, and lots more C. For those I use a BFS with the shank connected to the outer DAG ground return wiring net via an alligator clip lead. Just shove the tip under the ultor boot and up and in until solid contact is made.

Ed

On Mon, 25 Jun 2018 21:08:10 -0700, you wrote:

On Mon, Jun 25, 2018 at 08:40 pm, Jeff Urban wrote:

On Mon, Jun 25, 2018 at 07:45 pm, Jim Ford wrote:

then short the exposed tip (which is at the end of the red lead that goes to
the crt) to
metalwork. If there is a spark, then the CRT is receiving the output from

the

multiplier

No. That is not proper procedure, this is not a lawn mower. You let that ultor
voltage arc you are beating the shit out of a bunch of precision resistors in
the chain for the CRT bias, stressing old unobtainium parts and once some of
that shorts out you'll be sorry. If it is already shorted the voltage does not
build up, if you make it so it can, the stress on the rest of it will be more
severe as the capacitance discharges.

The arc method of testing is fine on an old "Madman Muntz", but not for Tek
scopes.

It may not work here, but a way to test for high voltage was to test
for the leakage from the HV line, or the magnetic fields. Take an old
neon lamp (or perhaps a small CCFL lamp. tape it to an insulating
stick or plastic rod. Do NOT hold any of the metallic conductors, and
bring it close to the HV transformer or the HV lead. You may see some
activity. You're not touching any of the leads to any other lead,
you're looking for a field to perhaps ionize the neon.

May work, may not. Worked on old TV sets, but that was far more HV.

Harvey

So, sorry, I disagree.

I think that Jeff makes a good point here. There is no reason to test like that. You are very likely to burn up some good components through feedback, excess current or over-voltage. Causing any sort of high voltage supply to jump an arc requires a much higher voltage than is found in a normal circuit. For example, a car coil that may send 4-6kV across a good spark plug can be forced to produce 10 times as much voltage when made to jump a large gap, but they will not last long doing that. There are simply too many delicate parts in one of these scopes to use that method of testing.

On Mon, Jun 25, 2018 at 09:56 pm, Ed Breya wrote:

Jeff, I have to disagree with your disagreement - when you short the PDA lead
of a scope CRT to ground, you are (rapidly) discharging the filter capacitance
of the internal carbon DAG or metallization to the outside coatings or
surfaces like the (grounded) mu-shield. It is a common safety procedure to
keep it safe during later work or CRT handling, and has nothing to do with the
cathode circuit. There are risks though, like getting zapped yourself, or
slipping during unplugging, letting the Alden connector tip accidentally hit
circuitry instead of ground. It would be safer, but less exciting to discharge
it in a less intense way via a high resistance, but when you only have two
hands, each holding one end of a recently unplugged connector set, it's hard
to add components to your situation. Direct shorting to ground is the most
expedient method.

Sometimes the Aldens are tight after years of sitting, and are difficult to
pull apart, then all of a sudden let loose easily. Before attempting
disengagement, twist one end against the other to break the surface adhesion -
especially if one part is silicone rubber, which tends to hang on tightly.
Once the housings are free from each other, the main thing holding is the
contacts. Then carefully apply the pulling force between the halves. When you
feel it snap loose, you can slowly withdraw and expose the hot tip and touch
it to the chassis.

I have done it plenty of times, and gotten zapped a bit approximately once,
but it's harmless as long you're not surprised and lose control. My method
nowadays is to wear leather work gloves, and grab the connector halves between
the thumb and index finger of each hand, and levering between the thumb
knuckles. The gloves soften up the forces on the thumbs, and help spread the
arc if you happen to screw up. With practice, this can give very good control.

Now, TV CRTs are a different story - usually higher voltage, and lots more C.
For those I use a BFS with the shank connected to the outer DAG ground return
wiring net via an alligator clip lead. Just shove the tip under the ultor boot
and up and in until solid contact is made.

Ed

I got bit unplugging my 485 a few years ago I have no idea how it happened. Now I use linesman's pliers lined with rubber so to not damage anything, to pull the lead out. I do wear leather gloves when taking HV measurements.

then short the exposed tip (which is at the end of the red lead that
goes to the crt) to metalwork. If there is a spark, then the CRT is
receiving the output from the multiplier

No. That is not proper procedure, this is not a lawn mower. You let that ultor voltage arc you are
beating the shit out of a bunch of precision resistors in the chain for the CRT bias, stressing old
unobtainium parts and once some of that shorts out you'll be sorry. If it is already shorted the
voltage
does not build up, if you make it so it can, the stress on the rest of it will be more severe as the
capacitance discharges.

The arc method of testing is fine on an old "Madman Muntz", but not for Tek scopes.

So, sorry, I disagree.

You clearly did not read what I said. You short the exposed tip OF THE CRT to ground. The CRT is a
capacitor which stores the charge from the multiplier for a long time.

1. YOU TURN THE SCOPE OFF - OK? You might unplug it from the mains just to be sure.
2. Then you disconnect the HT CONNECTOR BETWEEN THE MULTIPLIER AND CRT - got that? You know - THE LONG
WHITE PLUG AND SOCKET WITH THE RED WIRES COMING OUT.
3. THEN YOU SHORT THE EXPOSED TIP OF THE CRT WIRE TO GROUND. I just hope I don't need to draw a
picture.

So absolutely nothing at all gets stressed! I'm sorry to shout, but you really should have read and
understood my post before rubbishing the procedure.

Craig

I think that Jeff makes a good point here. There is no reason to test like that. You are very
likely to
burn up some good components through feedback, excess current or over-voltage. Causing any sort
of high voltage supply to jump an arc requires a much higher voltage than is found in a normal
circuit.
For example, a car coil that may send 4-6kV across a good spark plug can be forced to produce 10
times
as much voltage when made to jump a large gap, but they will not last long doing that. There are
simply too many delicate parts in one of these scopes to use that method of testing.

--
Michael Lynch
Dardanelle, AR

What on earth is the matter with this list at the moment - do you not all read English? Read my
original mail, and my shouty point by point explanation!!!!!

Craig

I got bit unplugging my 485 a few years ago I have no idea how it happened. Now I use linesman's
pliers lined with rubber so to not damage anything, to pull the lead out. I do wear leather gloves
when
taking HV measurements.

You do have to be somewhat careful. There is usually a very high resistance between the connector and
the CRT - some tens of megs - and the DAG coating is also resistive. So although a belt from the
stored charge in the CRT feels alarming, the current is tiny - in the tens of microamp region. The
really dangerous ones are in the 500 series of tubed/valved oscilloscopes, because some of the
voltages to do with anode/plate supplies are potentially lethal because of the hundreds of mA current
available.

Whatever I'm doing with higher voltages that pack a punch I use the old trick of keeping one hand in
my pocket - so you can't get a current flowing from one hand to the other via your chest and beating
heart.

And the other way to prevent damage for those who don't happen to have linesman's pliers is to use a
section of bicycle inner tyre wrapped around what you are trying to pull apart and regular pliers.
That is the standard way of disassembling fountain pens without damaging the parts.

Craig