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Re: Tek 7603 missing readout but present when beam finder pressed

Karin Johnson
 

Is it possible that the positioning of the readout is off screen in normal mode? Then when pushing the beamfinder the readout is brought on screen?
I believe there is an adjustment on the readout board to position the readout on screen at the proper locations.
Karin


Re: Repair of a 7S14

SCMenasian
 

Useful to know - Thanks for the info

Stephen Menasian


Re: Repair of a 7S14

Jeff Kruth
 

Once you cut the foil thru, you can use a larger tip soldering iron and tin the unwanted piece with solder, then heat it well and simply push it off the board! I have made many simple circuits with cut and peel but heat from tinning helps loosen the glue and makes removal clean and simple. A new X-acto knife blade is useful for getting under the edge and lifting the foil on larger patches. I have made 2 foot square patch antennas like this, but the heat is a must. The soldering iron and the tinning of the unwanted section really helps. I have made SMT boards the same way.

 Jeff KruthIn a message dated 9/19/2021 9:56:11 AM Eastern Standard Time, scm@menasians.com writes: Jeff:

You might try something along th elines of the photo I uploaded. I realize you probably don't have a milling machine; howerver there are other ways of accomplishing the same result.

A dremel tool or dental drill might work; but it it is a bit crude.

You might try the following:

1) Cut a piece of FR4 to the finished size of the adapter.
2) with a pointed (#11) scalpel or X-Acto knife, cut completely through the copper to create the desired final pattern.
3) Starting from the edge and using the scalpel, start to peel a piece of undesired copper off the board.
4) Finish removing it by grabbing with pliers and pull it off the board. It should come off cleanly.
5) Repeat 3 and 4 for the remaining undesired copper.

Stephen Menasian


Re: Tek 7603 missing readout but present when beam finder pressed

 

Check the CRT Grid Bias - step 4A of the calibration procedure. This adjustment changes as CRT's age and affects the normal vs beam finder behavior.

--
Bob Haas


Re: Tek 7603 missing readout but present when beam finder pressed

satbeginner
 

Just to be sure: you did adjust the readout intensity knob beneath the crt?
Only on half of the dial of that potmeter the readout is actually "on".

Sorry if you already adjusted that one .

Leo


Tek 7603 missing readout but present when beam finder pressed

Roy Kalawsky
 

I’ve just acquired a 7603 after many years of searching. Everything spot on except the readout display is missing. However, when the beam finder pressed it appears compressed with the other traces and its brightness can be controlled with the readout control. Anyone any clues?

Cheers Roy


Re: Repair of a 7S14

SCMenasian
 

Jeff:

You might try something along th elines of the photo I uploaded. I realize you probably don't have a milling machine; howerver there are other ways of accomplishing the same result.

A dremel tool or dental drill might work; but it it is a bit crude.

You might try the following:

1) Cut a piece of FR4 to the finished size of the adapter.
2) with a pointed (#11) scalpel or X-Acto knife, cut completely through the copper to create the desired final pattern.
3) Starting from the edge and using the scalpel, start to peel a piece of undesired copper off the board.
4) Finish removing it by grabbing with pliers and pull it off the board. It should come off cleanly.
5) Repeat 3 and 4 for the remaining undesired copper.

Stephen Menasian


Re: Help needed bringing a 555 back to life

Morris Odell
 

The way the -150 regulator circuit works is this:

V609 provides a stable voltage reference of -85 volts by being fed current from the -150 line through R608. Twin triode V624 is a differential amplifier that compares the -85 reference with -85 divided down from the -150 by the voltage divider consisting of R615, 616 (pot) and 617. C618 controls the AC feedback loop response. It it's leaky it will throw the whole regulator out of alignment and would cause the -150 output to go low. The error voltage at pin 6 of V624 is amplified by V634 and used to control the grid bias of both sections of V647 which is the series pass regulator. V647 is bypassed by R646 and 647 to provide a base load current. If the -150 is low then V647 is not conducting enough.

The 5651 is a voltage reference tube and is not supposed to carry more than a milliamp or two. It gets its current through R608. The voltage across it should not be more than 85 volts. If it's not at that voltage regardless of whether it's lit, check or replace R608 (33K) and the 5651 and see what happens. Also check C618 (0.01 uF). If it's a black beauty or bumblebee cap with colored stripes, replace it and any others you can find.They are notorious for going leaky.

You need to get the voltage reference right before anything else.

Morris


Re: Repair of a 7S14

 

It seems that epoxy doesn't adhere very well to a shiny copper surface; I managed to pull one of the copper strips off of the epoxy body while trying to bend them to make contact with the pads on the sampler board.

I made a second version of the chip carrier, this time I roughened up the surface of the copper foil before applying the epoxy, and I applied a second layer of epoxy on the opposite side of the copper strips just for good measure (and to provide an enclosed space for the SOT-23 part).

Here is a picture of the new chip carrier with a sample SOT-23 part for dimensional verification: https://groups.io/g/TekScopes/photo/267375/3305181?p=Created%2C%2C%2C20%2C2%2C0%2C0

This was a little harder to make than the first one, because I had to peel the assembly off the tape before the epoxy was completely cured (while it was still "green") so that the second layer of epoxy would stick it. Applying the second layer of epoxy caused some epoxy to get places I didn't want it, and I had to do a bit of careful carving with an Xacto knife to clear the intended pads and make enough space for the STO-23 part.

Waiting was still the hardest part, but I'm not sure I really want to work with a faster setting epoxy; it's very convenient to have an hour or so where the epoxy is in a state that is easy to work.

-- Jeff Dutky


Re: Help needed bringing a 555 back to life

Harvey White
 

From what little I remember about VR tubes, as long as it fires, it *ought* to have the correct voltage.  I think I remember hearing about VR tubes that didn't fire,  but then they didn't light up.

IIRC, the 5651 was intended not as a power regulator tube, like the OA3 series (able to handle a fair amount of current as a parallel regulator to a load),  but was intended to have a fairly narrow range of current, to be a voltage reference to an amplifier, rather than a direct regulator itself.

I'd suggest looking at the supply voltage to the regulator, the voltage of the tube itself, and see if you can remove any tubes looking at that regulation voltage (to eliminate loading and shorts, if practical).

If the tube doesn't fire and show the correct voltage, I'd say it's bad.  Depending on what supplies you have, you could test it separately, but I seem to remember somewhere around 5 ma nominal for the current through the tube.   It wasn't designed for much power dissipation at all.

Harvey

On 9/19/2021 12:05 AM, selinica.harbinger@gmail.com wrote:
I double checked the connection on V647, they're at chassis potential. They're both tied together and directly to the metal mount of the tube socket, testing their connection to ground on any point in the chassis gives 2milliOhms at the most.
I may just re-cap the power supply portion sans electrolytics and swap out every carbon composite resistor in the -150V section. The only other alternative coming to mind is checking thermals given the spot on the bottom of L790 and perhaps there is just a bad resistor somewhere that measures acceptable enough cold.
Could the 5651 be possibly fried from going outside of the voltage it can regulate or overcurrent if another component failed or is that a very unlikely outcome?





Re: Help needed bringing a 555 back to life

Selinica Harbinger
 

I double checked the connection on V647, they're at chassis potential. They're both tied together and directly to the metal mount of the tube socket, testing their connection to ground on any point in the chassis gives 2milliOhms at the most.
I may just re-cap the power supply portion sans electrolytics and swap out every carbon composite resistor in the -150V section. The only other alternative coming to mind is checking thermals given the spot on the bottom of L790 and perhaps there is just a bad resistor somewhere that measures acceptable enough cold.
Could the 5651 be possibly fried from going outside of the voltage it can regulate or overcurrent if another component failed or is that a very unlikely outcome?


2465 has no Cursors?

Allan
 

Hi All

I have a 2465 that seems to work eg. turns on and has a display etc. except it has no Cursors. The PSU board has been recapped and all voltages look fine. You can push the V & T buttons and the display changes and you can turn the knobs and the values change but you never see cursors? Any ideas?

Thanks

cheers..Allan


Re: 465 Trigger View/Bandwidth Switch Question

Mark Vincent
 

Ed,

I tried mine and your switch is operating normally. All of the way in, it will come out some to the point it should be in. Since you will be replacing parts already, clean the switch as a precaution. Clean the others as well if you have not already done so. It will not hurt.

I replaced the power supply condensers in mine recently due to many on this group saying one or more are likely to give trouble. At the age of these, replacement with new good ones is a good idea. I am glad I listened to others here about this model, 7603 and other 400 series. I already replaced the other electrolytics and some were replaced with radial film types (1-5mfd at 100V or higher that are originally axial) Be SURE to use jumpers between the ground holes of the original tabs. Some will use more than one as a ground jumper. This is if you are not using the new made round boards that allow a radial or modern snap in type into a FP style hole.

Mark


Re: 465 Trigger View/Bandwidth Switch Question

 

Ed,

The TRIG VIEW position is NOT supposed to latch, in fact it should pop out immediately rather than "slowly." I have lubricated the TRIG VIEW/BW LIMIT switches in a 475 using WD-40, but I'm not sure that this is the preferred (or advisable) method.

-- Jeff Dutky


465 Trigger View/Bandwidth Switch Question

Ed Pavlovic
 

Have a question regarding the operation of the “Trigger View/Bandwidth” switch on my 465 is it supposed to latch when pushed in for the trigger view? Mine latches when pulled out to reduce the bandwidth but slowly pops out when pushed all the way in.

Is this normal, or something I need to add to the list of things to do after the PS capacitors?

Ed Pavlovic


Re: 7D20 attenuators issues, calibration questions

Zentronics42@...
 

Randy,
I might be able to help there. In terms of the attenuator there Is a prescribed cleaning method from Tek that most here adhere too. I am currently running an experiment with deoxit D100 non aerosol in the attenuator section of a 465B. This will most likely be responded with I am going to destroy the scope. To which my only response can be it was a last resort cleaning as I did not want to use sandpaper because the scope was stored in a barn before I got it so it was in desperate need of EXTENCIVE cleaning. Deodit was applied with a needle bottle and with as little as possible to do the job and a VERY small gauge needle. So far so good it has been a few months now and the attenuator is still working great. However I would NOT recommend this as a first pass.

If some relays end up being bad I had to replace some relays in a AA501A I designed some adaptor boards and used some coto relays in place of the failed reed relays. So there are many options available to get the plugin up and running again.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Randy Newman
Sent: Saturday, September 18, 2021 5:32 PM
To: TekScopes@groups.io
Subject: [TekScopes] 7D20 attenuators issues, calibration questions

Hi all:
I’m restating my earlier topic “7k plug-in cleaning to be more descriptive of my current issue.
I recently purchased. 7D20 from that “e”-place. It arrived excellently packaged. I finally plugged it into my 7854 to see how it worked ( seller stated working, which it does mostly).
Self test reports error codes related to attenuators.
Before digging into the repair manual much (my bench is a very temporary setup, so only had so much time), I fed calibrator 400 mV into both ch 1&2. Ch 1 seems ok above 50 mV/div, but ch 2 seems inaccurate at any attenuators range. Btw, a bit of Old Home Week in this, in that I used one of these as a wee engineer.

I saw one post about substrate pad cleaning. I’ve not had time or space to start a disassembly….and am reticent to start, as I already have several repair projects in disassembly, and am hoping I really kept all the fasteners with them…(ADD and loose parts not a good mix).

Anyway, I’m a bit suspicious that some corrosion may be at fault since the front aluminum frame shows some oxidation. I also noted that the plastic trim around some of the gain/centering adjustments had either crumbled earlier, or in cases, crumbled when touched by my adjustment tool. Plugin is a bit on the geriatric side.

I’ve seen the early firmware post re: error codes (thanks!), but do not believe that is my issue.
I’d appreciate any cleanup/calibration advice anyone has.
ALSO, I noted the flex extender cables used for calibration. Not having these, I see that doing a cal with what I have on hand is not readily doable, except with repeated plug-in insert/extract cycles.

So, to summarize:
1) how best to clean attenuators?
2) extender cables options
3) and,,,would repeated self-test execution clean off relay contacts via wiping action?
( and yes, I saw Dennis’ discussion about vertically-sourced Tek design relays….too bad they did not have someone knowledgeable about relays, and things like materials science w/r/t contacts)

Am looking forward to getting this plugin fixed!


7D20 attenuators issues, calibration questions

Randy Newman
 

Hi all:
I’m restating my earlier topic “7k plug-in cleaning to be more descriptive of my current issue.
I recently purchased. 7D20 from that “e”-place. It arrived excellently packaged. I finally plugged it into my 7854 to see how it worked ( seller stated working, which it does mostly).
Self test reports error codes related to attenuators.
Before digging into the repair manual much (my bench is a very temporary setup, so only had so much time), I fed calibrator 400 mV into both ch 1&2. Ch 1 seems ok above 50 mV/div, but ch 2 seems inaccurate at any attenuators range. Btw, a bit of Old Home Week in this, in that I used one of these as a wee engineer.

I saw one post about substrate pad cleaning. I’ve not had time or space to start a disassembly….and am reticent to start, as I already have several repair projects in disassembly, and am hoping I really kept all the fasteners with them…(ADD and loose parts not a good mix).

Anyway, I’m a bit suspicious that some corrosion may be at fault since the front aluminum frame shows some oxidation. I also noted that the plastic trim around some of the gain/centering adjustments had either crumbled earlier, or in cases, crumbled when touched by my adjustment tool. Plugin is a bit on the geriatric side.

I’ve seen the early firmware post re: error codes (thanks!), but do not believe that is my issue.
I’d appreciate any cleanup/calibration advice anyone has.
ALSO, I noted the flex extender cables used for calibration. Not having these, I see that doing a cal with what I have on hand is not readily doable, except with repeated plug-in insert/extract cycles.

So, to summarize:
1) how best to clean attenuators?
2) extender cables options
3) and,,,would repeated self-test execution clean off relay contacts via wiping action?
( and yes, I saw Dennis’ discussion about vertically-sourced Tek design relays….too bad they did not have someone knowledgeable about relays, and things like materials science w/r/t contacts)

Am looking forward to getting this plugin fixed!


Re: TDS754 Vertical Input Coupling set to GND

EricJ
 

How much noise are we talking about, and in what vertical range? Both of my 754s produce as flat a line as they're going to when ground coupled but there will always be some noise present. If we're talking a barely squiggly line that doesn't even deviate a unit from the baseline it's likely nothing to worry about. Of it's deviating by divisions, you obviously have a problem. Give us the vert range, set a min/max measurement and see what you get. As the other fellow said, not enough information.--EricSent from my Galaxy

-------- Original message --------From: Mike Lemcke <mlemcke@wi.rr.com> Date: 9/18/21 4:03 AM (GMT-06:00) To: TekScopes@groups.io Subject: [TekScopes] TDS754 Vertical Input Coupling set to GND I have purchased a TDS754 scope. Self Tests PASS. When I went to the Vertical Menu and then to Coupling, I pressed the GND button. Instead of getting a Horizontal Flat Line at the CH1 marker, I saw noise. It is the same on all 4 channels. The DC and AC inputs are fine.I have read the TDS754 User and Service Manuals, but they are not clear about seeing a flat line when set to GND.I have a TDS224, have used a TDS2000 series scope at work and I contacted a friend who uses a TDS2000 series scope. They all produce a flat line when set to GND.Should a TDS754 produce a Flat line when the Vertical Input Coupling is set to GND?I would like to know if this the way a TDS754 works because I can return the scope if this is a problem.


Re: TDS754 Vertical Input Coupling set to GND

Siggi
 

All scopes exhibit some amount of noise at all times, even in GND coupling.
The amount of noise you see will depend on the vertical attenuator setting,
the bandwidth of the scope, and the display settings.
If you enable the 20MHz bandwidth limit, the noise should drop, and the
noise should be greatest at the most sensitive vertical settings.

See e.g. this video https://youtu.be/Znwp0pK8Tzk for some background.

This being said, your new scope may well be exhibiting excessive noise, or
there may e.g. be power supply ripple bleeding into your traces. It’s hard
to say from your description.

Maybe if you upload some pictures, it’d be easier to say.


Þann lau., 18. sep. 2021 kl. 05:03 skrifaði Mike Lemcke <mlemcke@wi.rr.com>:

I have purchased a TDS754 scope. Self Tests PASS. When I went to the
Vertical Menu and then to Coupling, I pressed the GND button. Instead of
getting a Horizontal Flat Line at the CH1 marker, I saw noise. It is the
same on all 4 channels. The DC and AC inputs are fine.
I have read the TDS754 User and Service Manuals, but they are not clear
about seeing a flat line when set to GND.
I have a TDS224, have used a TDS2000 series scope at work and I contacted
a friend who uses a TDS2000 series scope. They all produce a flat line when
set to GND.
Should a TDS754 produce a Flat line when the Vertical Input Coupling is
set to GND?
I would like to know if this the way a TDS754 works because I can return
the scope if this is a problem.






Re: Curious behavior of a CRT

TV7
 

Tried replying before not sure if it worked...

The publication was https://vintagetek.org/troubleshooting-your-oscilloscope/

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