Topics

Tek 465 Turns on, No Dot, No Trace

Stephen
 

Hi,

I have this Tektronix 465 that I got a few days ago. I knew it had that issue, and I thought I could fix it. It turns out to be more difficult than I anticipated. Here’s the issue:

The scope turns on, the fan spins, the graticule illumination is working, when I inject a signal from my function generator, I can see the trigger light go on and off whenever I turn the knob. Everything seems to be working, except there is no trace or dot on the display, and the beam finder is also silent.
As per the troubleshooting steps in the manual, I’m checking the CRT circuit to the best of my ability.

I’ve checked Q1404 and R1404, and they are fine. I even replaced Q1404 just to be safe.
Voltages are not what I would expect: Base: 3.53V, Emiter: 2.95V, Collector: 2.97V

Voltages have been checked as well, and 2 of them are very low:
TP1536: dead on -55V
TP1548: 15.05V
TP1558: 4.74V (too low)
TP1568: -6.3V (way too low!)
TP1518: 111.2V

I can’t check the HV (-2450V) because I don’t have a High Voltage probe. My DVM will fry.

I could use some help...

 

Ok, first, check the fuse F1419. If blown, check C1419 for short.

Second, get the supplies working correctly. I suspect C1552 5000uF and C1562 3000uF as being low capacity. Confirm by looking at the ripple on the +5 and -8 test points.

You can use the next higher standard value and a higher voltage for replacements. Be careful removing the old caps as there is track on both sides of the board.  Radial lead caps work fine but you need to put some jumpers tieing the three ground points together for the can caps.

A little searching the archives for 465 and 475 power supply tips would help you.

You didn't mention the serial number so this is for the late model s/n
250000 scopes.
Bottom line is my bet is on the old power supply caps.

On 7/9/2020 4:58 PM, stephen.nabet wrote:
Hi,

I have this Tektronix 465 that I got a few days ago. I knew it had that issue, and I thought I could fix it. It turns out to be more difficult than I anticipated. Here’s the issue:

The scope turns on, the fan spins, the graticule illumination is working, when I inject a signal from my function generator, I can see the trigger light go on and off whenever I turn the knob. Everything seems to be working, except there is no trace or dot on the display, and the beam finder is also silent.
As per the troubleshooting steps in the manual, I’m checking the CRT circuit to the best of my ability.

I’ve checked Q1404 and R1404, and they are fine. I even replaced Q1404 just to be safe.
Voltages are not what I would expect: Base: 3.53V, Emiter: 2.95V, Collector: 2.97V

Voltages have been checked as well, and 2 of them are very low:
TP1536: dead on -55V
TP1548: 15.05V
TP1558: 4.74V (too low)
TP1568: -6.3V (way too low!)
TP1518: 111.2V

I can’t check the HV (-2450V) because I don’t have a High Voltage probe. My DVM will fry.

I could use some help...

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Stephen
 

On Thu, Jul 9, 2020 at 03:48 PM, Tom Miller wrote:


Ok, first, check the fuse F1419. If blown, check C1419 for short.
Thanks for answering.
Yes. I didn’t mention it, but I have already. Fuse is fine.


Second, get the supplies working correctly. I suspect C1552 5000uF and
C1562 3000uF as being low capacity. Confirm by looking at the ripple on
the +5 and -8 test points.
Yep, will do tomorrow. 5:15AM over here.

A little searching the archives for 465 and 475 power supply tips would
help you.
Indeed, thanks.

You didn't mention the serial number so this is for the late model s/n
>250000 scopes.
I wished I knew it myself. It was apparently scraped. However, boards are dated 1971 and Dutch names on stickers, so I suspect an early model made in Holland.

Bottom line is my bet is on the old power supply caps.
That would do that just with a few volts off? Hmmm.., 🤔

Stephen
 

On Thu, Jul 9, 2020 at 03:48 PM, Tom Miller wrote:

Second, get the supplies working correctly. I suspect C1552 5000uF and
C1562 3000uF as being low capacity. Confirm by looking at the ripple on
the +5 and -8 test points.
Lots of ripple indeed!! You were right!!
I’m gonna change those 2 and report back.
I never would’ve thought that would have such a drastic impact on the trace.

Is there a way to check and adjust the -2450V HV without a HV probe??

Thanks again.

Stephen
 

On Thu, Jul 9, 2020 at 04:22 PM, Stephen wrote:


On Thu, Jul 9, 2020 at 03:48 PM, Tom Miller wrote:

A little searching the archives for 465 and 475 power supply tips would
help you.
Where do I find the archives? I’m new here.

Thanks

Albert Otten
 

Where do I find the archives? I’m new here.
Stephan, that's just short for "old messages at the Tekscopes website". A lot of information and hints there. You also should know about Tekwiki , w140.com/tekwiki/wiki/Main_Page .
Albert

Stephen
 

On Fri, Jul 10, 2020 at 02:28 AM, Albert Otten wrote:


Where do I find the archives? I’m new here.
Stephan, that's just short for "old messages at the Tekscopes website". A lot
of information and hints there. You also should know about Tekwiki ,
w140.com/tekwiki/wiki/Main_Page .
Albert
I see. Of course I know about TekWiki.
Thank you again.
Any advice regarding my other question About HV?

 

What test equipment do you have access to? You might be able to make up a divider string to extend the range of a DMM to cover the 2500 volts needed to measure the cathode voltage. For example, if your DMM has a 10 meg input, then making up a 90 meg stack from 9 ten-meg, 1% resistors installed in a glass or plastic tube (Bic pen?) would give a X10 probe.

You would want to get that voltage right before adjusting any H & V adjustments.

Regards

On 7/10/2020 7:11 AM, Stephen wrote:
On Thu, Jul 9, 2020 at 03:48 PM, Tom Miller wrote:

Second, get the supplies working correctly. I suspect C1552 5000uF and
C1562 3000uF as being low capacity. Confirm by looking at the ripple on
the +5 and -8 test points.
Lots of ripple indeed!! You were right!!
I’m gonna change those 2 and report back.
I never would’ve thought that would have such a drastic impact on the trace.

Is there a way to check and adjust the -2450V HV without a HV probe??

Thanks again.

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strictly that should refer to <https://groups.io/g/TekScopes>

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 July 2020 14:43
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 465 Turns on, No Dot, No Trace

On Fri, Jul 10, 2020 at 02:28 AM, Albert Otten wrote:


Where do I find the archives? I’m new here.
Stephan, that's just short for "old messages at the Tekscopes website". A lot
of information and hints there. You also should know about Tekwiki ,
w140.com/tekwiki/wiki/Main_Page .
Albert
I see. Of course I know about TekWiki.
Thank you again.
Any advice regarding my other question About HV?

Stephen
 

In the process of replacing those 2 caps.
They are not easy to take out.
Replacing the 3000uF 35v with a modern 3300uF 63V, and the 5000uF 25V with a modern 4700uF 63V (or maybe a 6800uF 63V), whichever fits better...

Paul Amaranth
 

Some notes:

The caps have 4 pins: 3 ground and 1 +. When you replace the cap all 3
ground pads must be connected together.

There are little pcb adapters floating around that adapt a modern snap cap
to that footprint. You can buy them on ebay and they make a nice repair.
There are also gerbers floating around and, if you get desperate, you can
etch them yourself.

Use 105C caps for replacements.

Use good desoldering equipment to get the caps out. Overheating the board
will lead to trace separation. Some people cut the ground lugs on top of
the board to make it easier to desolder the pin.

If I have to replace 1 or 2, I generally do all of them. This is a common
failure.

Unless you play with HV frequently, I'd go find a HV probe off of ebay.
That may or may not be lethal but you want avoid being in the circuit
path.

Paul

On Fri, Jul 10, 2020 at 09:34:22AM -0700, Stephen wrote:
In the process of replacing those 2 caps.
They are not easy to take out.
Replacing the 3000uF 35v with a modern 3300uF 63V, and the 5000uF 25V with a modern 4700uF 63V (or maybe a 6800uF 63V), whichever fits better...





!DSPAM:5f08989e109681011215572!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows

Keith Erickson
 

The HV actual potential is not that critical for operation of the scope, my opinion.

Keith in Wayzata, MN

On Jul 10, 2020, at 11:46 AM, Paul Amaranth <paul@...> wrote:

Some notes:

The caps have 4 pins: 3 ground and 1 +. When you replace the cap all 3
ground pads must be connected together.

There are little pcb adapters floating around that adapt a modern snap cap
to that footprint. You can buy them on ebay and they make a nice repair.
There are also gerbers floating around and, if you get desperate, you can
etch them yourself.

Use 105C caps for replacements.

Use good desoldering equipment to get the caps out. Overheating the board
will lead to trace separation. Some people cut the ground lugs on top of
the board to make it easier to desolder the pin.

If I have to replace 1 or 2, I generally do all of them. This is a common
failure.

Unless you play with HV frequently, I'd go find a HV probe off of ebay.
That may or may not be lethal but you want avoid being in the circuit
path.

Paul

On Fri, Jul 10, 2020 at 09:34:22AM -0700, Stephen wrote:
In the process of replacing those 2 caps.
They are not easy to take out.
Replacing the 3000uF 35v with a modern 3300uF 63V, and the 5000uF 25V with a modern 4700uF 63V (or maybe a 6800uF 63V), whichever fits better...





!DSPAM:5f08989e109681011215572!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows


Stephen
 

On Fri, Jul 10, 2020 at 05:49 AM, Keith Erickson wrote:

Ok

The HV actual potential is not that critical for operation of the scope, my
opinion.

Keith in Wayzata, MN
On Jul 10, 2020, at 11:46 AM, Paul Amaranth <paul@...> wrote:

Some notes:

The caps have 4 pins: 3 ground and 1 +. When you replace the cap all 3
ground pads must be connected together.

There are little pcb adapters floating around that adapt a modern snap cap
to that footprint. You can buy them on ebay and they make a nice repair.
There are also gerbers floating around and, if you get desperate, you can
etch them yourself.

Use 105C caps for replacements.

Use good desoldering equipment to get the caps out. Overheating the board
will lead to trace separation. Some people cut the ground lugs on top of
the board to make it easier to desolder the pin.

If I have to replace 1 or 2, I generally do all of them. This is a common
failure.

Unless you play with HV frequently, I'd go find a HV probe off of ebay.
That may or may not be lethal but you want avoid being in the circuit
path.

Paul

On Fri, Jul 10, 2020 at 09:34:22AM -0700, Stephen wrote:
In the process of replacing those 2 caps.
They are not easy to take out.
Replacing the 3000uF 35v with a modern 3300uF 63V, and the 5000uF 25V with
a modern 4700uF 63V (or maybe a 6800uF 63V), whichever fits better...





!DSPAM:5f08989e109681011215572!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows


Stephen
 

On Fri, Jul 10, 2020 at 05:46 AM, Paul Amaranth wrote:


Some notes:

The caps have 4 pins: 3 ground and 1 +. When you replace the cap all 3
ground pads must be connected together.
Yes, I’ve done scopes a few weeks back. A 2215 and a 2235. Same deal, just much much easier to access.

There are little pcb adapters floating around that adapt a modern snap cap
to that footprint. You can buy them on ebay and they make a nice repair.
There are also gerbers floating around and, if you get desperate, you can
etch them yourself.
I’ll just run jumper wires. It works just fine.

Use 105C caps for replacements.
All I found were 85C caps at my local electronics store. They should be fine for now. I’ll replace the rest of them after all is working properly.

Unless you play with HV frequently, I'd go find a HV probe off of ebay.
That may or may not be lethal but you want avoid being in the circuit
path.

Paul
The only time I come across HV is this....

Will report back when it’s completed. Hopefully with a nice trace.

Colin Herbert
 

I don't suppose you live in London, UK and anywhere near Wimbledon, do you? I have a P6015A probe that is good for around 20KV. Mind you, I would ask that you don't fiddle with the compensation adjustments. Incidentally, the P6015A probe doesn't use the nasty Freon dielectric.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 July 2020 12:12
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 465 Turns on, No Dot, No Trace

On Thu, Jul 9, 2020 at 03:48 PM, Tom Miller wrote:

Second, get the supplies working correctly. I suspect C1552 5000uF and
C1562 3000uF as being low capacity. Confirm by looking at the ripple on
the +5 and -8 test points.
Lots of ripple indeed!! You were right!!
I’m gonna change those 2 and report back.
I never would’ve thought that would have such a drastic impact on the trace.

Is there a way to check and adjust the -2450V HV without a HV probe??

Thanks again.

Stephen
 

On Fri, Jul 10, 2020 at 06:36 AM, Colin Herbert wrote:


I don't suppose you live in London, UK and anywhere near Wimbledon, do you? I
have a P6015A probe that is good for around 20KV. Mind you, I would ask that
you don't fiddle with the compensation adjustments. Incidentally, the P6015A
probe doesn't use the nasty Freon dielectric.
Colin.
Unfortunately no. I’m not very far, but I can’t just stop by either. I’m in Paris/France.
But thanks for the offer. I appreciate it.

Stephen
 

I successfully changed the 2 bad caps. The good news is no more ripple whatsoever, and all voltages are absolutely right on the money. However, bad news is nothing as changed; still no trace, dot, or beam finder...
And to top it all off the “ON” indicator light doesn’t light up anymore. And I’m pretty sure it did before. All others do (X10, Uncal, Volt/Div, trigger...), and graticule illumination is also working. I took the little bulb out, and it works fine with a 3V battery. I measured the voltages for that bulb and it reads 4.85V. Could it be an indication for another issue? This is madness. It lights up with a 3V battery, but doesn’t in circuit with 4.85V.
Also, voltages across Q1404 haven’t changed much. A few millivolts, I think.

This scope is officially driving me nuts. I don’t know what else to do...

 

Can you go back and measure all the other low voltages in the HV circuit? The base being positive so much says the HV oscillator is not running.

Measure all the points shown on the schematic for the primary of T1420. Let's see what is going on there.

A common problem is a shorted HV multiplier (U1432) that stops the oscillator from running.  Lifting the ground lead of the multiplier lets the oscillator run and the -2450 supply comes up allowing HV regulation. If that turns out to be the issue, there are several options you can take.

On 7/10/2020 6:40 PM, Stephen wrote:
I successfully changed the 2 bad caps. The good news is no more ripple whatsoever, and all voltages are absolutely right on the money. However, bad news is nothing as changed; still no trace, dot, or beam finder...
And to top it all off the “ON” indicator light doesn’t light up anymore. And I’m pretty sure it did before. All others do (X10, Uncal, Volt/Div, trigger...), and graticule illumination is also working. I took the little bulb out, and it works fine with a 3V battery. I measured the voltages for that bulb and it reads 4.85V. Could it be an indication for another issue? This is madness. It lights up with a 3V battery, but doesn’t in circuit with 4.85V.
Also, voltages across Q1404 haven’t changed much. A few millivolts, I think.

This scope is officially driving me nuts. I don’t know what else to do...

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I should say the circuitry Driving the primary of T1420, Including Q1418.

Regards

On 7/10/2020 7:09 PM, Tom Miller wrote:
Can you go back and measure all the other low voltages in the HV circuit? The base being positive so much says the HV oscillator is not running.

Measure all the points shown on the schematic for the primary of T1420. Let's see what is going on there.

A common problem is a shorted HV multiplier (U1432) that stops the oscillator from running.  Lifting the ground lead of the multiplier lets the oscillator run and the -2450 supply comes up allowing HV regulation. If that turns out to be the issue, there are several options you can take.



On 7/10/2020 6:40 PM, Stephen wrote:
I successfully changed the 2 bad caps. The good news is no more ripple whatsoever, and all voltages are absolutely right on the money.  However, bad news is nothing as changed; still no trace, dot, or beam finder...
And to top it all off the “ON” indicator light doesn’t light up anymore.  And I’m pretty sure it did before.  All others do (X10, Uncal, Volt/Div, trigger...), and graticule illumination is also working.  I took the little bulb out, and it works fine with a 3V battery.  I measured the voltages for that bulb and it reads 4.85V.  Could it be an indication for another issue?  This is madness.  It lights up with a 3V battery, but doesn’t in circuit with 4.85V.
Also, voltages across Q1404 haven’t changed much.  A few millivolts, I think.

This scope is officially driving me nuts.  I don’t know what else to do...


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Stephen
 

On Fri, Jul 10, 2020 at 12:10 PM, Tom Miller wrote:


Can you go back and measure all the other low voltages in the HV
circuit? The base being positive so much says the HV oscillator is not
running.

Measure all the points shown on the schematic for the primary of T1420.
Let's see what is going on there.

A common problem is a shorted HV multiplier (U1432) that stops the
oscillator from running.  Lifting the ground lead of the multiplier lets
the oscillator run and the -2450 supply comes up allowing HV regulation.
If that turns out to be the issue, there are several options you can take.
All I could find to measure is at the fuse, and I found 23.43V. Another TP I found was TP1594, and I have 9.72V.
TP1486 reads from 14.59V to 31.98V depending on the Intensity pot level.
I didn’t find any other points to measure.
As for lifting the ground leg of the HV multiplier, I don’t have access to it. It’s buried and enclosed on the other side of the board.