Date   

TM515 Suitcase 500 Series Cardcage/Power Supply Bail (Wire Stand) Replacement?

tma.7ta@...
 

Greetings,

I have a TM515 with a missing wire stand (referred to as a bail) which appears to have been made from ~3/16" stainless steel rod. I wonder if anyone here has had experience with obtaining or possibly fabricating one?

Thanks in advance for any enlightenment!

tma


Re: 475A horizontal amplifier problem

Dave Wise
 

It's usually simple... once you know what it is.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of toby via groups.io <toby=telegraphics.com.au@groups.io>
Sent: Tuesday, October 06, 2020 6:17 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475A horizontal amplifier problem

On 2020-10-06 8:28 a.m., Jim Hall wrote:
PROBLEM SOLVED - After checking the components, voltages, and waveforms in the horizontal amplifier circuit and verifying that the outputs of the amplifier were correct, I took the advice of Tom M. and Tom L. to consider the CRT. The problem was that the connection to the CRT's left plate was disconnected. Much effort and patience was required to reattach the wire to the CRT through the hole in the interface board. . Many thanks to both Tom M. and Tom L for their help in locating the problem.
Well that's great news. Another TekScopes success we can all learn from...

--Toby


Jim





Re: 475A horizontal amplifier problem

Simon
 

I don’t know how you got access to the X deflection pins on the CRT through the hole in the interface board. Keyhole surgery? It might have been easier to remove the CRT after unsoldering the X amp output wires (red and green go through the hole). Attach a puller wire to them so that you can pull them back through the hole after checking the X deflection connections. Even so that is fiddly as you have to remove the 4 Y deflection wires, and they are not easy to put back.
Simon


Re: 475A horizontal amplifier problem

toby@...
 

On 2020-10-06 8:28 a.m., Jim Hall wrote:
PROBLEM SOLVED - After checking the components, voltages, and waveforms in the horizontal amplifier circuit and verifying that the outputs of the amplifier were correct, I took the advice of Tom M. and Tom L. to consider the CRT. The problem was that the connection to the CRT's left plate was disconnected. Much effort and patience was required to reattach the wire to the CRT through the hole in the interface board. . Many thanks to both Tom M. and Tom L for their help in locating the problem.
Well that's great news. Another TekScopes success we can all learn from...

--Toby


Jim





Re: 475A horizontal amplifier problem

Jim Hall
 

PROBLEM SOLVED - After checking the components, voltages, and waveforms in the horizontal amplifier circuit and verifying that the outputs of the amplifier were correct, I took the advice of Tom M. and Tom L. to consider the CRT. The problem was that the connection to the CRT's left plate was disconnected. Much effort and patience was required to reattach the wire to the CRT through the hole in the interface board. . Many thanks to both Tom M. and Tom L for their help in locating the problem.

Jim


Re: Is my Tek 468 beyond repair?

jrseattle
 

Since there was a request for this in the above discussion, I uploaded an image of the Tektronix 468 service rom to the files section. It's in a directory called "Tektronix 468 Service Rom"


Re: Yet another attempt to fix a 2465B

Stephen Hanselman
 

Chuck,

Thanks that makes very good sense. Although for us pin spacing is not a big issue. I have several small PCBs that take standard pin spaced modern caps and have either pins, screw terminals, or large diameter wire to go to the OEM pub connectors.

We will put you ideas to use, again thank you!

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Oct 5, 2020, at 16:54, Chuck Harris <cfharris@erols.com> wrote:

I prefer a capacitor that is higher voltage, and larger
diameter... more like the original's diameter... over a
smaller diameter, lower voltage capacitor for a couple
of reasons.

First, to make a higher voltage capacitor, you have to
apply a thicker layer of dielectric oxide. If you keep
the foil area the same, a higher voltage capacitor will
have lower capacitance than a lower voltage capacitor of
the same size.

To compensate for the reduced capacitance of a higher
voltage capacitor, the manufacturer can do a few things:
1) increase the number of turns of foil, which will
increase the ESL of the capacitor.
2) increase the height of the capacitor, which will lower
the resistance of the aluminum foil, and reduce the
ESR of the capacitor.
3) or do both.

Second, if the higher voltage results in a larger
capacitor, it will have more surface area from which to
radiate heat.

If you look at the tables for a given capacitor family,
you will almost always find that a higher voltage capacitor
of the same capacitance will have a lower ESR than its lower
voltage cousin.

My other reason has to do with lead spacing. If you
use a smaller capacitor, it will almost always have
narrower lead spacing than the original. If you simply
stick the leads in the holes, and press down until the
capacitor stops going down, the leads will be under
stress, and the seal will be stretched. This makes
the capacitor more likely to leak its electrolyte.

In the olden days, it was a very bad thing to use
an electrolytic capacitor that was much higher in WV
than the circuit requires. Today, it isn't. Today's
electrolytic capacitors will maintain their oxide layer
regardless of the voltage applied. This is because
the oxide layer is anodized onto the foil surface before
the capacitor is assembled. They can do this now because
the modern electrolytes are perfectly neutral to aluminum
and aluminum oxide.

-Chuck Harris

Stephen Hanselman wrote:
Chuck,

If you have low ESR, high ripple current and high temp, close to or higher capacitance right at or above working voltage (which is what we do) why is physical size important?

steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck Harris
Sent: Monday, October 5, 2020 6:22 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yet another attempt to fix a 2465B

Grayson,

To some people, a capacitor is a capacitor is a capacitor....

Not all electrolytic capacitors work well in switching power supplies. To get the best life out of your power supply capacitors You have to use the best long life (5K hours+), low ESR, low impedance, high ripple current capacitor you can afford. Further it has to be 105C rated or better.

I recommend looking for capacitors that are similarly sized to the originals. To get that size, go to higher value and higher voltage in your replacements. Higher voltage capacitors generally have lower ESR and higher ripple current ratings, rated for switching power supply use.

The guy that did the recap botched it, you should replace them again, only this time with properly selected capacitors.

I replace all of the 180uf40V and 250uf20V caps with a single type, 330uf 50V from United Chemicon. Panasonic also makes a suitable capacitor in that value. Nichicon doesn't (didn't?).

These capacitors are the most critical in the scope. I always find one or two of the original caps in these 6 positions that is bad. They handle +/-5V, +/- 15V, and the 5V digital.

The 5V digital pair are C1110 and C1111.

What I generally find with bad recap jobs is the capacitor's values are slavishly matched, with a capacitor that is about
1/4 the size of the original. Usually something that is a general purpose capacitor, not a switching rated capacitor.

-Chuck Harris

Grayson Evans wrote:
I have had a nice 2465B for about 6 years that I bought at Dayton (hamvention). It worked. About a year ago it quit when I turned it on one morning. It has the same symptoms as Dave's in his EEvlog #1203 on youtube. All the front panel LEDs light up but that's it.
Voltages are all in spec except the +5V, it is 4.5V with 400 mVpp ripple. The +15 volt supply also has the same 400 mVpp ripple, but voltage is good.
Whoever had it before me did a very nice recap of the power supply, very nice resoldering work. Looks like a factory job. Replaced the SMDs on the logic board with regular electrolytic.
THe only thing I can figure out is that at least some caps around the +5 and +15 supply need replacing again.
Looks like Tek assumed the power supply would not need servicing. Hard to get in and out and impossible to work on while it's installed. If it breaks, board level replacement. I can't see anyway to troubleshoot the board set.
Has anyone ever hooked up 120V to the boards out of the scope to try to troubleshoot it? Doesn't seem practical or safe.
BTW, I am plowing through the giant eevblog thread, but only up to page 11 (of 68!). Don't know if I can make it.
Thanks,
Grayson



















Re: Yet another attempt to fix a 2465B

toby@...
 

On 2020-10-05 8:12 p.m., Tom Lee wrote:
Thanks, Chuck, for an excellent tutorial!

-- Tom
Seconded. Another Chuck Harris classic to "star" in my inbox for later
rumination...

--Toby


Re: Yet another attempt to fix a 2465B

Tom Lee
 

Thanks, Chuck, for an excellent tutorial!

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/5/2020 16:53, Chuck Harris wrote:
I prefer a capacitor that is higher voltage, and larger
diameter... more like the original's diameter... over a
smaller diameter, lower voltage capacitor for a couple
of reasons.

First, to make a higher voltage capacitor, you have to
apply a thicker layer of dielectric oxide. If you keep
the foil area the same, a higher voltage capacitor will
have lower capacitance than a lower voltage capacitor of
the same size.

To compensate for the reduced capacitance of a higher
voltage capacitor, the manufacturer can do a few things:
1) increase the number of turns of foil, which will
increase the ESL of the capacitor.
2) increase the height of the capacitor, which will lower
the resistance of the aluminum foil, and reduce the
ESR of the capacitor.
3) or do both.

Second, if the higher voltage results in a larger
capacitor, it will have more surface area from which to
radiate heat.

If you look at the tables for a given capacitor family,
you will almost always find that a higher voltage capacitor
of the same capacitance will have a lower ESR than its lower
voltage cousin.

My other reason has to do with lead spacing. If you
use a smaller capacitor, it will almost always have
narrower lead spacing than the original. If you simply
stick the leads in the holes, and press down until the
capacitor stops going down, the leads will be under
stress, and the seal will be stretched. This makes
the capacitor more likely to leak its electrolyte.

In the olden days, it was a very bad thing to use
an electrolytic capacitor that was much higher in WV
than the circuit requires. Today, it isn't. Today's
electrolytic capacitors will maintain their oxide layer
regardless of the voltage applied. This is because
the oxide layer is anodized onto the foil surface before
the capacitor is assembled. They can do this now because
the modern electrolytes are perfectly neutral to aluminum
and aluminum oxide.

-Chuck Harris

Stephen Hanselman wrote:
Chuck,

If you have low ESR, high ripple current and high temp, close to or higher capacitance right at or above working voltage (which is what we do) why is physical size important?

steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck Harris
Sent: Monday, October 5, 2020 6:22 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yet another attempt to fix a 2465B

Grayson,

To some people, a capacitor is a capacitor is a capacitor....

Not all electrolytic capacitors work well in switching power supplies. To get the best life out of your power supply capacitors You have to use the best long life (5K hours+), low ESR, low impedance, high ripple current capacitor you can afford. Further it has to be 105C rated or better.

I recommend looking for capacitors that are similarly sized to the originals. To get that size, go to higher value and higher voltage in your replacements. Higher voltage capacitors generally have lower ESR and higher ripple current ratings, rated for switching power supply use.

The guy that did the recap botched it, you should replace them again, only this time with properly selected capacitors.

I replace all of the 180uf40V and 250uf20V caps with a single type, 330uf 50V from United Chemicon. Panasonic also makes a suitable capacitor in that value. Nichicon doesn't (didn't?).

These capacitors are the most critical in the scope. I always find one or two of the original caps in these 6 positions that is bad. They handle +/-5V, +/- 15V, and the 5V digital.

The 5V digital pair are C1110 and C1111.

What I generally find with bad recap jobs is the capacitor's values are slavishly matched, with a capacitor that is about
1/4 the size of the original. Usually something that is a general purpose capacitor, not a switching rated capacitor.

-Chuck Harris

Grayson Evans wrote:
I have had a nice 2465B for about 6 years that I bought at Dayton (hamvention). It worked. About a year ago it quit when I turned it on one morning. It has the same symptoms as Dave's in his EEvlog #1203 on youtube. All the front panel LEDs light up but that's it.
Voltages are all in spec except the +5V, it is 4.5V with 400 mVpp ripple. The +15 volt supply also has the same 400 mVpp ripple, but voltage is good.
Whoever had it before me did a very nice recap of the power supply, very nice resoldering work. Looks like a factory job. Replaced the SMDs on the logic board with regular electrolytic.
THe only thing I can figure out is that at least some caps around the +5 and +15 supply need replacing again.
Looks like Tek assumed the power supply would not need servicing. Hard to get in and out and impossible to work on while it's installed. If it breaks, board level replacement. I can't see anyway to troubleshoot the board set.
Has anyone ever hooked up 120V to the boards out of the scope to try to troubleshoot it? Doesn't seem practical or safe.
BTW, I am plowing through the giant eevblog thread, but only up to page 11 (of 68!). Don't know if I can make it.
Thanks,
Grayson
















Re: Yet another attempt to fix a 2465B

Chuck Harris <cfharris@...>
 

I prefer a capacitor that is higher voltage, and larger
diameter... more like the original's diameter... over a
smaller diameter, lower voltage capacitor for a couple
of reasons.

First, to make a higher voltage capacitor, you have to
apply a thicker layer of dielectric oxide. If you keep
the foil area the same, a higher voltage capacitor will
have lower capacitance than a lower voltage capacitor of
the same size.

To compensate for the reduced capacitance of a higher
voltage capacitor, the manufacturer can do a few things:
1) increase the number of turns of foil, which will
increase the ESL of the capacitor.
2) increase the height of the capacitor, which will lower
the resistance of the aluminum foil, and reduce the
ESR of the capacitor.
3) or do both.

Second, if the higher voltage results in a larger
capacitor, it will have more surface area from which to
radiate heat.

If you look at the tables for a given capacitor family,
you will almost always find that a higher voltage capacitor
of the same capacitance will have a lower ESR than its lower
voltage cousin.

My other reason has to do with lead spacing. If you
use a smaller capacitor, it will almost always have
narrower lead spacing than the original. If you simply
stick the leads in the holes, and press down until the
capacitor stops going down, the leads will be under
stress, and the seal will be stretched. This makes
the capacitor more likely to leak its electrolyte.

In the olden days, it was a very bad thing to use
an electrolytic capacitor that was much higher in WV
than the circuit requires. Today, it isn't. Today's
electrolytic capacitors will maintain their oxide layer
regardless of the voltage applied. This is because
the oxide layer is anodized onto the foil surface before
the capacitor is assembled. They can do this now because
the modern electrolytes are perfectly neutral to aluminum
and aluminum oxide.

-Chuck Harris

Stephen Hanselman wrote:

Chuck,

If you have low ESR, high ripple current and high temp, close to or higher capacitance right at or above working voltage (which is what we do) why is physical size important?

steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck Harris
Sent: Monday, October 5, 2020 6:22 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yet another attempt to fix a 2465B

Grayson,

To some people, a capacitor is a capacitor is a capacitor....

Not all electrolytic capacitors work well in switching power supplies. To get the best life out of your power supply capacitors You have to use the best long life (5K hours+), low ESR, low impedance, high ripple current capacitor you can afford. Further it has to be 105C rated or better.

I recommend looking for capacitors that are similarly sized to the originals. To get that size, go to higher value and higher voltage in your replacements. Higher voltage capacitors generally have lower ESR and higher ripple current ratings, rated for switching power supply use.

The guy that did the recap botched it, you should replace them again, only this time with properly selected capacitors.

I replace all of the 180uf40V and 250uf20V caps with a single type, 330uf 50V from United Chemicon. Panasonic also makes a suitable capacitor in that value. Nichicon doesn't (didn't?).

These capacitors are the most critical in the scope. I always find one or two of the original caps in these 6 positions that is bad. They handle +/-5V, +/- 15V, and the 5V digital.

The 5V digital pair are C1110 and C1111.

What I generally find with bad recap jobs is the capacitor's values are slavishly matched, with a capacitor that is about
1/4 the size of the original. Usually something that is a general purpose capacitor, not a switching rated capacitor.

-Chuck Harris

Grayson Evans wrote:
I have had a nice 2465B for about 6 years that I bought at Dayton (hamvention). It worked. About a year ago it quit when I turned it on one morning. It has the same symptoms as Dave's in his EEvlog #1203 on youtube. All the front panel LEDs light up but that's it.
Voltages are all in spec except the +5V, it is 4.5V with 400 mVpp ripple. The +15 volt supply also has the same 400 mVpp ripple, but voltage is good.
Whoever had it before me did a very nice recap of the power supply, very nice resoldering work. Looks like a factory job. Replaced the SMDs on the logic board with regular electrolytic.
THe only thing I can figure out is that at least some caps around the +5 and +15 supply need replacing again.
Looks like Tek assumed the power supply would not need servicing. Hard to get in and out and impossible to work on while it's installed. If it breaks, board level replacement. I can't see anyway to troubleshoot the board set.
Has anyone ever hooked up 120V to the boards out of the scope to try to troubleshoot it? Doesn't seem practical or safe.
BTW, I am plowing through the giant eevblog thread, but only up to page 11 (of 68!). Don't know if I can make it.
Thanks,
Grayson
















Re: 475A horizontal amplifier problem

Tom Lee
 

Sorry that I haven't read the entire thread, but to localize the problem, you should first verify whether the outputs of the horizontal amplifier are swinging the amount that they should. If they are, then your problem lies in the interconnect to the crt, or the crt itself. A revealing test is to engage the 10x magnification function to see if you are able to overscan the screen. If you are, then you have sufficient swing capability in the output amp, and the finger begins to point toward a gain insufficiency.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/5/2020 13:36, Jim Hall wrote:
Since this was one of the scopes that I have purchased on eBay, I don't know its history. The waveforms look correct on the deflection plates. However, compared to those on the plates of my good 475A, they are compressed horizontally.




Re: 475A horizontal amplifier problem

 

In that case, it might be well worth pulling the tube and inspecting for broken bits of glass in the neck. The 475A is well worth saving.

Regards

On 10/5/2020 4:36 PM, Jim Hall wrote:
Since this was one of the scopes that I have purchased on eBay, I don't know its history. The waveforms look correct on the deflection plates. However, compared to those on the plates of my good 475A, they are compressed horizontally.



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This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Re: 475A horizontal amplifier problem

Jim Hall
 

Since this was one of the scopes that I have purchased on eBay, I don't know its history. The waveforms look correct on the deflection plates. However, compared to those on the plates of my good 475A, they are compressed horizontally.


Re: 7623A Storage problem

NigelP
 

Another good source was the old SGS or SGS-Ates 2N3055H, possibly also SGS-Thomson as it later became known; can't remember when we stopped doing hometaxial devices, it was a long time ago!

Regards

Nigel G8AYM (ex STMicroelectronics, SGS-Thomson, SGS-Semiconductor and SGS-Ates)


Re: Yet another attempt to fix a 2465B

Leon Robinson
 

More can area, better cooling. 


Leon Robinson  K5JLR

-------- Original message --------
From: Stephen Hanselman <kc4sw.io@kc4sw.com>
Date: 10/05/2020 11:51 AM (GMT-06:00)
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yet another attempt to fix a 2465B

Chuck,

If you have low ESR, high ripple current and high temp, close to or higher capacitance right at or above working voltage (which is what we do) why is physical size important?

steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck Harris
Sent: Monday, October 5, 2020 6:22 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yet another attempt to fix a 2465B

Grayson,

To some people, a capacitor is a capacitor is a capacitor....

Not all electrolytic capacitors work well in switching power supplies.  To get the best life out of your power supply capacitors You have to use the best long life (5K hours+), low ESR, low impedance, high ripple current capacitor you can afford.  Further it has to be 105C rated or better.

I recommend looking for capacitors that are similarly sized to the originals.  To get that size, go to higher value and higher voltage in your replacements.  Higher voltage capacitors generally have lower ESR and higher ripple current ratings, rated for switching power supply use.

The guy that did the recap botched it, you should replace them again, only this time with properly selected capacitors.

I replace all of the 180uf40V and 250uf20V caps with a single type, 330uf 50V from United Chemicon.  Panasonic also makes a suitable capacitor in that value.  Nichicon doesn't (didn't?).

These capacitors are the most critical in the scope.  I always find one or two of the original caps in these 6 positions that is bad.  They handle +/-5V, +/- 15V, and the 5V digital.

The 5V digital pair are C1110 and C1111.

What I generally find with bad recap jobs is the capacitor's values are slavishly matched, with a capacitor that is about
1/4 the size of the original.  Usually something that is a general purpose capacitor, not a switching rated capacitor.

-Chuck Harris

Grayson Evans wrote:
I have had a nice 2465B for about 6 years that I bought at Dayton (hamvention).  It worked. About a year ago it quit when I turned it on one morning.  It has the same symptoms as Dave's in his EEvlog #1203 on youtube.  All the front panel LEDs light up but that's it.
Voltages are all in spec except the +5V, it is 4.5V with 400 mVpp ripple.  The +15 volt supply also has the same 400 mVpp ripple, but voltage is good.
Whoever had it before me did a very nice recap of the power supply, very nice resoldering work.  Looks like a factory job.  Replaced the SMDs on the logic board with regular electrolytic.
THe only thing I can figure out is that at least some caps around the +5 and +15 supply need replacing again.
Looks like Tek assumed the power supply would not need servicing.  Hard to get in and out and impossible to work on while it's installed.  If it breaks, board level replacement. I can't see anyway to troubleshoot the board set.
Has anyone ever hooked up 120V to the boards out of the scope to try to troubleshoot it?  Doesn't seem practical or safe.
BTW, I am plowing through the giant eevblog thread, but only up to page 11 (of 68!).  Don't know if I can make it.
Thanks,
Grayson






Re: 475A horizontal amplifier problem

 

Was the scope dropped? I have seen where the CRT internal glass support rods have broken causing similar problems. How do the waveforms look on  the H defection plates? They should be the same but inverted.

Tom

On 10/5/2020 2:38 PM, Jim Hall wrote:
Thanks for the suggestion Tom. I have now checked the resistors and compared the values to the parts list and those in the good scope. They all appear good. The waveform extends only one division to the left of center when I maximize the horizontal gain and use the position pot to move to the left. Something is preventing the beam from moving further left.



--
This email has been checked for viruses by Avast antivirus software.
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Re: 475A horizontal amplifier problem

Jim Hall
 

Thanks for the suggestion Tom. I have now checked the resistors and compared the values to the parts list and those in the good scope. They all appear good. The waveform extends only one division to the left of center when I maximize the horizontal gain and use the position pot to move to the left. Something is preventing the beam from moving further left.


Re: Yet another attempt to fix a 2465B

tekscopegroup@...
 

Once you had the two board power supply sandwich out more than two times, it will only take you a few minutes the next time.

Also highly recommended that once you start your recap, do only ONE cap at a time, so as not to mixup different caps in the wrong position. And be aware there is also a layout error, so again doing one cap at a time will also take care of it.

That EEVBlog thread is been required reading for anyone with a 2465 that needs attention, and an excellent source of first hand information, same as with this group.


Re: Yet another attempt to fix a 2465B

Stephen Hanselman
 

Chuck,

If you have low ESR, high ripple current and high temp, close to or higher capacitance right at or above working voltage (which is what we do) why is physical size important?

steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck Harris
Sent: Monday, October 5, 2020 6:22 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yet another attempt to fix a 2465B

Grayson,

To some people, a capacitor is a capacitor is a capacitor....

Not all electrolytic capacitors work well in switching power supplies. To get the best life out of your power supply capacitors You have to use the best long life (5K hours+), low ESR, low impedance, high ripple current capacitor you can afford. Further it has to be 105C rated or better.

I recommend looking for capacitors that are similarly sized to the originals. To get that size, go to higher value and higher voltage in your replacements. Higher voltage capacitors generally have lower ESR and higher ripple current ratings, rated for switching power supply use.

The guy that did the recap botched it, you should replace them again, only this time with properly selected capacitors.

I replace all of the 180uf40V and 250uf20V caps with a single type, 330uf 50V from United Chemicon. Panasonic also makes a suitable capacitor in that value. Nichicon doesn't (didn't?).

These capacitors are the most critical in the scope. I always find one or two of the original caps in these 6 positions that is bad. They handle +/-5V, +/- 15V, and the 5V digital.

The 5V digital pair are C1110 and C1111.

What I generally find with bad recap jobs is the capacitor's values are slavishly matched, with a capacitor that is about
1/4 the size of the original. Usually something that is a general purpose capacitor, not a switching rated capacitor.

-Chuck Harris

Grayson Evans wrote:
I have had a nice 2465B for about 6 years that I bought at Dayton (hamvention). It worked. About a year ago it quit when I turned it on one morning. It has the same symptoms as Dave's in his EEvlog #1203 on youtube. All the front panel LEDs light up but that's it.
Voltages are all in spec except the +5V, it is 4.5V with 400 mVpp ripple. The +15 volt supply also has the same 400 mVpp ripple, but voltage is good.
Whoever had it before me did a very nice recap of the power supply, very nice resoldering work. Looks like a factory job. Replaced the SMDs on the logic board with regular electrolytic.
THe only thing I can figure out is that at least some caps around the +5 and +15 supply need replacing again.
Looks like Tek assumed the power supply would not need servicing. Hard to get in and out and impossible to work on while it's installed. If it breaks, board level replacement. I can't see anyway to troubleshoot the board set.
Has anyone ever hooked up 120V to the boards out of the scope to try to troubleshoot it? Doesn't seem practical or safe.
BTW, I am plowing through the giant eevblog thread, but only up to page 11 (of 68!). Don't know if I can make it.
Thanks,
Grayson






Re: Is my Tek 468 beyond repair?

John
 

Well the good news is that some progress is being made. The board has been re-capped (except for the large can which I have been unable to remove) and the two 74S112 ICs have been replaced and mounted in sockets. Since it tested OK under a 470Ω load, the original crystal was replaced and the board returned back to the chassis and re-connected. The 5MHz clock is now stable and there is minimal ripple on the 5V line.

I have checked the wave-forms on the timer board and found that some are present, others are missing or incorrect.

For example, waveforms at 148, 149, 150, 151 and 157 (all directly associated with the clock) are all correct. A waveform is present at 147 but it does not match the diagram but is more like square wave. There is no waveform at 146/TP120 but the line is high. I couldn't reach some of the points on the board, for example 154 and 155, but nothing was happening at 156. Since be board is heavily interconnected with the CPU board, I am wondering whether this might be the issue.

I am still waiting for a replacement 8085. I checked and the 5MHz clock was present on pin 1 and 2.5MHz on pin 37 but still no ALE. Hopefully the replacement CPU will resolve that.

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