Date   

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

/Håkan


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


Re: 2246A Power supply failure turning on / off

 

On Wed, Aug 19, 2020 at 04:50 PM, JorgeTop wrote:


Any suggestion?
The two most common faults causing the P/S to go into burst mode I've seen on the 224x supplies
have been one or more shorted rectifier diodes on the secondary or a bad HV multiplier.
Another not so obvious fault is that the 0.1 ohm current limiting resistor has increased slightly
in value causing the supply to shut down prematurely.

/Håkan


Re: A possibly sick 7904A

Eric
 

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: 2246A Power supply failure turning on / off

Milan Trcka
 

A lot of potential problems seem to have been eliminated. Next I would
start looking for a potential overload on the power supply which may (or
may not) cause the PS to go into a shutdown to protect itself (electronic
fuse?). Another scope is likely needed to poke about the various sections,
starting with the first reference (5V?) and going up the voltage ladder.
This for checking time-related changes (caps charging etc.). Maybe
disconnecting the loads from the power supply might give you a clue whether
the problem is load related and which section is the offender on either
side. Unloaded supply may be easier to check for faulty components.
Unfortunately this level of troubleshooting needs to be done under power so
be careful as to not letting the smoke as well as not getting hurt. (FWIW)

Milan

On Wed, Aug 19, 2020 at 7:50 AM JorgeTop <jdavidtop@ieee.org> wrote:

Hi!

Some time ago I got a used 2246 oscilloscope which was working quite well
until recently. First it began to show a single point on the screen and
then it would return, or you just had to turn it off and turn it on again.

Soon after, it started to cycle on and off and sometimes I needed to turn
it off for a moment and turn it on again to get it working again.

Now it kept turning on and off cyclically without stabilizing. So far, I
have changed things like some electrolytic capacitors (I read right here
that it is a common fault), however I have not found all. I have also
changed zener diodes and some transistors without success.

With the service manual I have tried to measure some points however since
it turns on and off the voltage is erratic. I have not yet found a similar
power supply for sale so at the moment it is not an option and I would like
to be able to repair it.

Any suggestion?





Re: SC502 With Display Issues

Stephen
 

I understand. And you’re absolute right. I did with what I had available at the time.

Best Regards,

And thank you for your time and effort.

Sent from my iPhone 7
Stephen S. Nabet
stephen.nabet@gmail.com

On 19 Aug 2020, at 19:21, Dave Wise <david_wise@phoenix.com> wrote:



Do you think [oscillation] could be an issue in the low power supply section?
It's a much-talked-about complaint. In this particular case, it's unlikely since the transistors in question only operate in unusual cases - power off and overload, respectively.
But since we're doing Component Engineering figuring out a suitable retrofit part, why not put in 100% effort? Do work you can be proud of.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Stephen via groups.io <stephen.nabet=gmail.com@groups.io>
Sent: Wednesday, August 19, 2020 10:00 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] SC502 With Display Issues

On Wed, Aug 19, 2020 at 05:48 AM, Dave Wise wrote:


To replace 2N3565 in the SC502 power supply, BC639 is better than 2N2222A,
100MHz vs 300MHz. Under a dollar at Mouser. But the best choice is KSC1008.
It's only 30MHz - perfect to avoid oscillation - and even cheaper. Mind the
pinout.
Ooh ok. Now I understand. You were talking about oscillation. This is the thing I didn’t grasp before from your previous post. Thank you for clearing that out. Do you think that could bean issue in the low power supply section?

On a side note, I’m trying to find parts that are readily available at my local shops because it’s just a 20min ride from my place.
And I know that if something fails, I can easily go and get them without having to order, and wait for (sometimes) a week to 10 days to get them. Yes, it’s terrible, I know.
BC639 is available. Not the KSC1008. I’ll try that.








Re: SC502 With Display Issues

Dave Wise
 

Do you think [oscillation] could be an issue in the low power supply section?
It's a much-talked-about complaint. In this particular case, it's unlikely since the transistors in question only operate in unusual cases - power off and overload, respectively.
But since we're doing Component Engineering figuring out a suitable retrofit part, why not put in 100% effort? Do work you can be proud of.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Stephen via groups.io <stephen.nabet=gmail.com@groups.io>
Sent: Wednesday, August 19, 2020 10:00 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] SC502 With Display Issues

On Wed, Aug 19, 2020 at 05:48 AM, Dave Wise wrote:


To replace 2N3565 in the SC502 power supply, BC639 is better than 2N2222A,
100MHz vs 300MHz. Under a dollar at Mouser. But the best choice is KSC1008.
It's only 30MHz - perfect to avoid oscillation - and even cheaper. Mind the
pinout.
Ooh ok. Now I understand. You were talking about oscillation. This is the thing I didn’t grasp before from your previous post. Thank you for clearing that out. Do you think that could bean issue in the low power supply section?

On a side note, I’m trying to find parts that are readily available at my local shops because it’s just a 20min ride from my place.
And I know that if something fails, I can easily go and get them without having to order, and wait for (sometimes) a week to 10 days to get them. Yes, it’s terrible, I know.
BC639 is available. Not the KSC1008. I’ll try that.


Re: Oscilloscope Operator Training Kit - TNGTDS01

 

Thanks Brian. 

Searching online for information on the Velleman boards, I see that Jameco https://www.jameco.com/z/EDU06-Velleman-Oscilloscope-Tutor-Kit_2175568.html offers them for $29.99 .  Although inexpensive, the signals these boards generate are generally available from instruments on the bench top.  My interest in the Tektronix board is for the glitched signals it offers as a way to demonstrate the capture and storage capabilities of these DSOs for catching transient waveforms.  I have never owned a storage scope before, but on several occasions could sure have used one. 

Bruce, KG6OJI

6081 - 6100 of 176680