Date   

Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

 

You need to get the service manual - it tells you how to remove the CRT.

The problem is likely the silicone sealant where the EHT is connected has failed.

You'll need to clean off the old and re-seal. Please don't use an acetic acid cure silicone - get a neutral cure type.

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Greenpitu@gmail.com
Sent: 20 August 2020 12:40
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Hello Roger - thanks once again!

Went into a dark room and spotted the spark straight away. It's coming from the top right corner of the CRT. I can see the spark lighting through a very tiny opening that is available in the chassis.

Please see short video with the exact location: https://youtu.be/7CxqL82_3VI

Now, I have no idea how to get into that spot... Any thoughts?

I will get on with the other measurements and revert back. I think I can carefully and safely work my way through these checks.

Best regards
Luis


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Greenpitu@...
 

Hello Roger - thanks once again!

Went into a dark room and spotted the spark straight away. It's coming from the top right corner of the CRT. I can see the spark lighting through a very tiny opening that is available in the chassis.

Please see short video with the exact location: https://youtu.be/7CxqL82_3VI

Now, I have no idea how to get into that spot... Any thoughts?

I will get on with the other measurements and revert back. I think I can carefully and safely work my way through these checks.

Best regards
Luis


Re: Looking for front cover for 465 and/or 485

Tom Gardner
 

I've considered making custom covers from laser-cut birch ply.

That should be trivial given the ability to generate finger joints, e.g. https://en.makercase.com/#/basicbox (no recommendation, simply the first I googled)

On 20/08/20 07:07, dabono@gmail.com wrote:
Here's an interesting one - custom-made from clear acrylic. IMO it's a bit expensive ($85), about what you'd pay for an original Tektronix front cover.
https://www.ebay.com/itm/TEKTRONIX-465B-465-OSCILLOSCOPE-FRONT-COVER-CUSTOM-MADE-CLEAR-ACRYLIC/283951063134?hash=item421ccd605e:g:j5kAAOSwSiZfEbTg


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Roger Evans
 

A crackling sound from the front of the CRT is not good. If you take the scope into a dark room with the cover off you may see some flashes from the region where the high voltage lead attaches near the front of the CRT. In any case you need to clean that area with IPA, but wait for maybe 30 minutes after the scope is powered off to allow the EHT to discharge.

Can you do some measurements on TP322 and TP324? With the scope displaying Ch1, input selector to ground, and the trace on the vertical centre line, these two test points should measure close to zero volts. If not can you adjust the vertical position to get TP322 and TP324 to read the same value, and then where is the beam? Also the Ch1 vertical position control should be somewhere near the mid point of its travel.

If these tests come out OK then the fault is most likely in the vertical amplifier not being biassed correctly. The manual I have doesn't give any voltage readings around U440 but you could measure the resistances of R446, R447 and R448 and the voltages on each end of R446 and R447.

The bias on the output transistors is adjustable with R455 but don't move it yet as it affects the vertical calibration and frequency response. Measure the voltages on each end of R457 and R452 to make sure that the transistors are drawing some base current and the voltage across R454 to ensure that the variable resistor R455 has not gone open circuit.

It is also worth removing U440, cleaning the pins and reinserting. If the mounting allows, I would apply some IPA around the pin/socket area and leave for an hour or so to penetrate before trying to remove the IC - they can be very stubborn. Check that there is not a nut on the other side of the PCB holding it in!

At this point I am running well beyond my competence and if anyone else would like to add anything I would be very grateful.

Regards,

Roger


Re: 2246A Power supply failure turning on / off

Brian Cockburn
 

This https://www.rc-cam.com/forum/index.php?/topic/4165-tektronix-2245a-oscilloscope-smps-repair-re-cap/ may be of some interest.

On a side note to everyone; is there a cannonical design or schematic for a dummy load suitable for 224x PSUs?

Cheers, Brian.


Re: Looking for front cover for 465 and/or 485

dabono@...
 

Here's an interesting one - custom-made from clear acrylic. IMO it's a bit expensive ($85), about what you'd pay for an original Tektronix front cover.
https://www.ebay.com/itm/TEKTRONIX-465B-465-OSCILLOSCOPE-FRONT-COVER-CUSTOM-MADE-CLEAR-ACRYLIC/283951063134?hash=item421ccd605e:g:j5kAAOSwSiZfEbTg


Re: 2246A Power supply failure turning on / off

JorgeTop
 

By now I have removed almost all the electrolytic capacitors and have observed that they all have much higher capacitance than stated, for example 1000uF have 1400uf, 470uf go for 600-700uF. How troublesome can this be?

For the diodes I have removed one of the pins to perform the diode measurement with a multimeter in diode function and they seem normal. I have not found open or shorted diodes. Zener diodes, I have changed most, as well as some transistors.

It remains for me to change the MC310 and the IC that I have not found locally.

I'm going to review the 0.1Ohm resistor you mention.

Thanks, I will update this week


Re: A possibly sick 7904A

 

On Wed, Aug 19, 2020 at 11:04 PM, Eric wrote:


I will blaspheme here for a little if I will be indulged. Don't get me wrong I
do love the 7904A but for the VERY slow and the very fast above 1Ghz I will
take the screen of a digital scope. Seeing 1hZ sign waves on a CRO is not easy
with out a camera. of course then again.. I might be a noob
Very few of us use veteran analog 'scopes because they are better suited to the job. That's only true in some situations, if compared with fast-refreshing digital 'scopes.

Raymond


Re: FG501 repair

um-gs@...
 

Hi,
just want to continue with my lessons learned on the same subject.
The device was operative, suplly voltages were adjustable to their nominal values, but no output.
1. No output
a) open R251 and inject signal voltage: Voltage appears at output, so amplifier is working
b) checking voltage at junction R32/R34 when turning the frequency dial: voltage varies
c) checking voltage at output of U15 pin 6 : does not vary - replace U15 which was defect - oscillator is working again, output signal is generated
2. Sine wave output distorted and adjustment R150 has no effect
a) replacing both R150 and R170 allows adjustment of distortion free sine wave output
3. Output signal not at symmetrical duty cycle
a) adjustment of R45 (step7) has no effect
b) output voltage at U40 pin6 does not vary when R45 is adjusted
c) swiper of R45 constantly at zero
d) opening up/replacing of C40 solved the problem (it was shorted) - output duty cycle can be adjusted

Regards, Gordian


Re: A possibly sick 7904A

Eric
 

I will blaspheme here for a little if I will be indulged. Don't get me wrong I do love the 7904A but for the VERY slow and the very fast above 1Ghz I will take the screen of a digital scope. Seeing 1hZ sign waves on a CRO is not easy with out a camera. of course then again.. I might be a noob

Eric

On 8/19/2020 5:00 PM, Raymond Domp Frank wrote:
On Wed, Aug 19, 2020 at 10:47 PM, Eric wrote:

Due to the difficulty of being able to source a tube if I needed one.
That's been my excuse for having two or, better even, three copies of all models for a few years now. But we're treading on very different ground here...

Raymond


Re: A possibly sick 7904A

 

On Wed, Aug 19, 2020 at 10:47 PM, Eric wrote:


Due to the difficulty of being able to source a tube if I needed one.
That's been my excuse for having two or, better even, three copies of all models for a few years now. But we're treading on very different ground here...

Raymond


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Greenpitu@...
 

Hello Roger,

I am back with some measurements.

** Vertical Switching **
Both measurements taken in ALT mode, no probe attached, and lowest TIME/DIV setting.

TP364 (-2V and -0.102V)
TP374 (-2V and -0.071V)

** Trig View **
With calibrator signal feeding Trig In, Trig Source set to Ext

Trigger Level Centered: when the beam is at the centre of the screen, the beam width is just under 1x sub-division
Trigger Level +++: when the beam is at the highest pos, that is +2.5 divisions above centre, the beam is just over 2 sub-divisions in width
Trigger Level ---: when the beam is at the lowest pos, that is -1.0 divisions below centre, the beam is also just over 2 sub-divisions in width

When at the center, there is a fuzzy glimpse of the square signal. However, when on +++ or --- positions then beam becomes entirely flat.

** Q322 and Q324 **
Using tester got the following values:

Q322: NPN, Gain: 75, Vf: 707mV
Q323: NPN, Gain: 71, Vf: 701mV

I should say I got (I think) bad news. I started hearing concerning cracking sounds for the first time while I was running the sweep at its slowest speed. At first, I heard like 5-7 in rapid succession. I powered off the scope and waited a little while. The scope cover was removed at the time, so I didn't get too close to the circuitry just in case. These sounds weren't too friendly. I increased the sweep speed before I turned it back on. Unfortunately, the crackling sound still persist - it doesn't seem to be related to the speed at all. In fact, it seems to be coming from the front of the cathode ray tube, but I can't be certain.

I made a short video where I captured 2 or 3 of the crackling sounds. My phone was capping out the percussive effect somewhat; the real sound is higher in pitch and volume.

https://youtu.be/DgHwnqH9xJs

Is this a concern?


Re: A possibly sick 7904A

 

On Wed, Aug 19, 2020 at 10:47 PM, Eric wrote:


The lack of an MCP is why I went with the 7904 as apposed to the 7104. Due to
the difficulty of being able to source a tube if I needed one.
Not having an MCP CRT hardly ever is (or rather: was) a problem. It's not like "You don't have a good 'analog 'scope unless it has an MCP CRT"...

Raymond


Re: A possibly sick 7904A

 

On Wed, Aug 19, 2020 at 09:24 PM, Eric wrote:


I have shied away from the MCP CRT as read some where that those tubes were
all on borrowed time as even at very low levels on intensity there was some
slight phosphor damage.
I think that's generally true, though it shouldn't be exaggerated. Acceptable brightness levels are fine and the 'scope does have some protections.

OTOH, some people like to see how bright the image of their 'scope will go. That's not what these 'scopes were designed for:
A few years ago, I had a friend who proudly showed me the screen brightness of his newly acquired 7104, the only problem being that brightness couldn't be turned down. Obviously a DC restorer problem or the like. After repair there was very little permanent (local) loss of brightness and no burned spots were visible. Quite different from the HP 1727A analog storage 'scope that turned out to have burnt its target.

The CRT in the 2467 appears to be far more resilient than the much older design in the 7104. It has better protection as well I guess. At low/normal brightness levels, life should be fine.
I only use a 7104 when I especially feel like it. It's not the best choice as a regular 'scope. Its screen graticule size is a bit smaller than regular models' as well (8mm/div vs. 10mm/div).

AFAIK, the 2467BHD, with its MCP CRT, was intended for regular HDTV-work.

FWIW, the CRT of my 7104 is as new, as are the CRT's of my 2467B and 2467BHD.

Raymond


Re: A possibly sick 7904A

Eric
 

The lack of an MCP is why I went with the 7904 as apposed to the 7104. Due to the difficulty of being able to source a tube if I needed one.

On 8/19/2020 4:03 PM, Dave Daniel wrote:
AFAIK, the 7904A does *not* use and MCP CRT. The 7104 and 2467 do use MCP CRTs.

DaveD

On Aug 19, 2020, at 15:24, Eric <ericsp@gmail.com> wrote:

Looks like my frame needs a bit of a tune up then. Ill be working on this once I get the current plugin done. I have shied away from the MCP CRT as read some where that those tubes were all on borrowed time as even at very low levels on intensity there was some slight phosphor damage. Not sure if this turned out to be the case.

Eric

On 8/19/2020 8:48 AM, Chuck Harris wrote:
Your description is pretty accurate.

The more modern scopes have compensation circuitry
that changes the focus voltage with the instantaneous
intensity setting.... and changes the instantaneous
intensity settings for the different beam uses...

So, the intensity is separately controllable for the A
horizontal plugin, the B horizontal plugin, the readout,
and in some cases, the "intensified" horizontal A vs B
settings... but FOCUS, and ASTIGMATISM, each have only
one user control.

Each of these settings result in a different beam current,
which require a different focus/astigmatism voltage.

For the 7904A, which was one of the earlier adopters of
this enhancement, they have a circuit called Auto Focus,
and in the Performance check and Adjustment procedure,
page 5-12 of my manual, they explain how it gets adjusted.

The do the main focus adjustment with the beam very dim,
and then they adjust the Auto Focus circuit with the beam
at full intensity control position.

-Chuck Harris

Roger Evans via groups.io wrote:
I am not an expert on this, trained in physics not electronics. When you look at a low rep rate signal at 500ps/div the beam is on a very small fraction of the time, about 5ns every msec so one part in 200000. The readout is being triggered automatically and runs around 1kHz or so, I don't remember the actual clock speeds. So for the same brightness the signal trace has to carry maybe 1000 times the current compared with the readout, this means a higher density of electrons and the space charge can affect the beam focussing compared with a low current beam.

I tried putting a fast rise square wave into my 7904 at 1kHz and qualitatively I see what you see. I have to turn up the brightness a lot to see the trace at 1ns/div and it does defocus compared with the readout. I can improve the focus slightly and that worsens the focus of the readout significantly.

Maybe if we get some more comments we can decide who is unrealistic and who is easily satisfied. I have no idea what the factory specifications were.

Regards,

Roger




Re: Tek 465 Sweep Start Calibration

 

On Wed, Aug 19, 2020 at 09:59 PM, david wrote:


With Sweep start adjustment R1115 fully counter clockwise, the Intensified
sweep starts at 0.96 on Delay Time position dial,
What is the DTM mechanical max CCW reading ? It should be 0.20
http://www.hakanh.com/dl/docs/hardtofind/dtmsettings.pdf

/HÃ¥kan


Re: A possibly sick 7904A

 

On Wed, Aug 19, 2020 at 10:03 PM, Dave Daniel wrote:


AFAIK, the 7904A does *not* use and MCP CRT.
That's correct or you wouldn't experience the writing rate being as "limited" as with all the other regular models.

Raymond


Re: Last Call - Tek 222/224 Battery Charger Project

Jeff Davis
 

Just wanted to chime in and let people know that they're also available at a slightly lower cost on www.n0dy.com<http://www.n0dy.com>;. The cost there is lower because Ebay doesn't take a cut as a commission.

Thanks for the kind words, Henry!

Jeff

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Henry Martinez <hrmartinez@gmail.com>
Sent: Tuesday, August 18, 2020 6:58 PM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] Last Call - Tek 222/224 Battery Charger Project

Sorry if I'm late to the party,
Just wanted people to know the kits are still available on eBay and they work great. I just put one into my Tektronix 224 and it is performing exactly as advertised. Thanks Jeff for pulling this all together.


Re: A possibly sick 7904A

Dave Daniel
 

AFAIK, the 7904A does *not* use and MCP CRT. The 7104 and 2467 do use MCP CRTs.

DaveD

On Aug 19, 2020, at 15:24, Eric <ericsp@gmail.com> wrote:

Looks like my frame needs a bit of a tune up then. Ill be working on this once I get the current plugin done. I have shied away from the MCP CRT as read some where that those tubes were all on borrowed time as even at very low levels on intensity there was some slight phosphor damage. Not sure if this turned out to be the case.

Eric

On 8/19/2020 8:48 AM, Chuck Harris wrote:
Your description is pretty accurate.

The more modern scopes have compensation circuitry
that changes the focus voltage with the instantaneous
intensity setting.... and changes the instantaneous
intensity settings for the different beam uses...

So, the intensity is separately controllable for the A
horizontal plugin, the B horizontal plugin, the readout,
and in some cases, the "intensified" horizontal A vs B
settings... but FOCUS, and ASTIGMATISM, each have only
one user control.

Each of these settings result in a different beam current,
which require a different focus/astigmatism voltage.

For the 7904A, which was one of the earlier adopters of
this enhancement, they have a circuit called Auto Focus,
and in the Performance check and Adjustment procedure,
page 5-12 of my manual, they explain how it gets adjusted.

The do the main focus adjustment with the beam very dim,
and then they adjust the Auto Focus circuit with the beam
at full intensity control position.

-Chuck Harris

Roger Evans via groups.io wrote:
I am not an expert on this, trained in physics not electronics. When you look at a low rep rate signal at 500ps/div the beam is on a very small fraction of the time, about 5ns every msec so one part in 200000. The readout is being triggered automatically and runs around 1kHz or so, I don't remember the actual clock speeds. So for the same brightness the signal trace has to carry maybe 1000 times the current compared with the readout, this means a higher density of electrons and the space charge can affect the beam focussing compared with a low current beam.

I tried putting a fast rise square wave into my 7904 at 1kHz and qualitatively I see what you see. I have to turn up the brightness a lot to see the trace at 1ns/div and it does defocus compared with the readout. I can improve the focus slightly and that worsens the focus of the readout significantly.

Maybe if we get some more comments we can decide who is unrealistic and who is easily satisfied. I have no idea what the factory specifications were.

Regards,

Roger





Tek 465 Sweep Start Calibration

david
 

Hi guys, I need your help again, I am trying to do horizontal calibration on my 465 but I cannot set step one of calibration, "Check/Adjust Sweep Start and A Sweep Calibration", With Sweep start adjustment R1115 fully counter clockwise, the Intensified sweep starts at 0.96 on Delay Time position dial, cannot get it to 1.0, Is out of range of R1115. Trimmer R1115 is in the middle of a voltage divider between R1113, R1112 and R 1117. Has anybody had this problem? In service manual, parts list says R1113 is "196 ohm (NOM VALUE) SEL". My 465 has a 145 ohm resistor for R1113, changing R1113 to 196 ohm would probably get enough range to fix Sweep Start. I don't know where else to look for the problem. Also have a newer version of service manual where parts list says R1113 is "196 ohm". Does not say nominal value select. The rest of the horizontal cal went OK.
David

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