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Re: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe

Stephan Lonis
 

It wasn’t exactly easy to replace but got it done. Had to place my
soldering iron underneath rotary switch towards the back of the 7b92a at
which point I was wishing I had more then two hands and melt the solder to
pull out the bad cap. It was a cap soldered alongside one of the coils
coming into 15 volts. I replaced a few other caps while I was inside the
unit with some higher temp, higher quality caps. In all probably 5
capacitors but the main culprit was that tantalum on the 15 volt rail.
After that plugged the plug-in back in and it was working after that.


Re: Teitronix 492a : TUNING FAILURE - 1st LO

John Miles
 

Until you fix the first LO unlock error, it is normal for it to be sluggish. The CPU is wasting time trying to lock a loop that won't lock.

Later versions of the 49x analyzers had a menu option to disable the tuning routine, so the CPU would run normally in the presence of an error, but I don't believe there was a way to do that in the 492.

-- john, KE5FX

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Bent Andersen
Sent: Sunday, February 07, 2021 10:30 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Teitronix 492a : TUNING FAILURE - 1st LO

Hi Ulf

tnx fer reply...but I think it is the cpu board there is defect.... I made a new
video,,,https://photos.app.goo.gl/HhBVr7KVjceQgpqeA

Ben



Re: Extracting a buggered knob grubscrew

Paul McClay
 

On Tue, Feb 2, 2021 at 11:21 PM, snapdiode wrote:


Here's a key I found in my toolbox, surely the only reason I bought it was to
wrestle with a Tek set screw at some point.

https://www.ebay.ca/itm/0-9-3mm-Hex-Screwdriver-Kit-For-RC-Helicopter-Drone-Aircraft-Model-Repair-Tools/132854596436
1.27 & 1.3 mm drivers... if they actually differ by 0.03 mm that would suggest goodness indeed.


Re: sighting: Beaverton-built 5110 Mod 709V for Bently Nevada

Paul McClay
 

Thanks again for the add'l info - and for taking the time to transcribe it. I've added it to TekWiki.

Interesting that the timebase mode switch apparently differs between the doc & photographed units.

A couple more questions:

Is "L vs H" correct for the 5B10N switch mod? That seems odd when the function is, I assume, Left vertical amp vs _not_ Horizontal sweep.

Are "Description", "Bandwidth" & "Calibration" same-level headings? Or Description & Calibration with Bandwidth under Description? Or otherwise?

Thanks again for help with the real reference material.


Re: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe

Tom Lee
 

Glad that it was as simple as expected. That's a nice timebase, and I'm sure you'll enjoy using it.

-- Cheers,
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 2/7/2021 22:28, Stephan Lonis wrote:
Tracked it down to a bad tantalum on the 15 volt supply on the main interface board inside the 7b92a. Replaced the bad tantalum and now everything is working as it should.




Re: Teitronix 492a : TUNING FAILURE - 1st LO

Bent Andersen
 

Hi Ulf

tnx fer reply...but I think it is the cpu board there is defect.... I made a new video,,,https://photos.app.goo.gl/HhBVr7KVjceQgpqeA

Ben


Re: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe

Stephan Lonis
 

Tracked it down to a bad tantalum on the 15 volt supply on the main interface board inside the 7b92a. Replaced the bad tantalum and now everything is working as it should.


Re: Teitronix 492a : TUNING FAILURE - 1st LO

Bent Andersen
 

Hi Miguel

I have made a new video, and I think it is the CPU board there is defect... if you look at the video, you can see that the keypad is working slowly, and you can move the knops and 1-2sec later it move....

https://photos.app.goo.gl/HhBVr7KVjceQgpqeA

so i will try to look for bad component's maybe try the "cold-spray" !!!

Ben


Re: Extracting a buggered knob grubscrew

Frank DuVal
 

Kroil is excellent.

But also try 50/50 mix of ATF and Acetone. That's any automatic transmission fluid and Acetone.

Of course if you have to buy a quart of fluid and a quart of Acetone, one can of Kroil may be cheaper if available locally.

Frank DuVal

On 2/2/2021 4:44 PM, JJ wrote:
I used a drop of Kroil on a 7000 plugin knob set screw when it was frozen.
That stuff never lets me down. Of course, you need to use it before you
strip the screw head! And, you need to be patient - like a few drops over
an 8 hour period. Be careful that you don't get the stuff on the face of a
Tek instrument - it will likely take the print off. But, just about
anything other than a lightly water damped cloth will take the print off a
Tek instrument.

JJ


Re: 2465B CRT board values

Hirofumi Momose
 

Hello Chuck, Jon

Chuck wrote:
I haven't found a 2465B that has its best focus at 12:00
Oh.. My unit is just 'normal'. Understand.

Jon wrote:
"If it ain't broke don't fix it"
"leave well enough alone"
Now works. Best focus point of trace/readout is a bit different.
But no problem to read.
Yes ,no more tune and leave it.

Thank you.
Hirofumi JJ2PNX


Re: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe

Ed Breya
 

Yes Reinhard, if the bad caps aren't among the "easy" (to access) ones, you have to dig deeper, and possibly disassemble some things to get to them. Then having an idea of which supply and which sub-assembly is involved definitely helps to narrow it down, especially for the bigger, more complicated plug-ins. Murphy's Law would dictate that the bad caps will be the most inaccessible, which happens sometimes, but on single-wide ones, especially verticals, there aren't all that many Ta caps to begin with, and not many that are too hard to access. Horizontals tend to have more layers of stuff, but often can be quick-tested with simple disassembly if needed, or accessing from the back (board layout info from the manual helps here too) or other accessible points on the same nodes.

The quick test can actually be even quicker than I described, in cases where you know that all the caps are simply bypassing to ground, and not between supplies. I think this is almost always the case with 7K plug-ins. Instead of probing caps with two leads for the ohmmeter, one lead can be grounded, and the other one used to make two measurements - one from each cap lead. One will show ground continuity, and the other should be a reasonably high resistance, unless the cap or the line it's on is dumped to ground. You don't care which is which, only that one lead is ground, and the other far from it.

Ed


Re: TEK 465 S/N>25000 Power Supply Issue

Ozan
 

Hi Craig,
These voltages look OK for the given pin 7 voltage and the current through R1549 is very small at 7.2mA. All of this current has to come from U1524B to sink 22V supply. My best guess is collector supply of Q1544/Q1546 is not there. There is no value marked but should be above 17V.

Ozan


Oran,

Thanks for starting this discussion.
Here are the values you were asking about.
When everything is connected, what voltages do you see:
At 15V TP. 1.675vdc
At the emitter of Q1546. 1.683vdc
At the base of Q1546. 2.223vdc
pin 7 of U1524B 2.988vdc
base of Q1548B. 2.084vdc
Voltage across R1549 (this tells us how much current is pulled from Q1546).
0.008vdc

We are looking for a possible high current out of U1524B pin 7 (~ 10mA).

Craig


Re: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe

n49ex
 

I agree in general, except in this case, given how densely packed the 7B92A is, it may be easier to know up front which power supply is the offender. And having to trace that power net through the unit using the schematic is a good learning experience anyway👿. And I would not be surprised if it is the entry filter cap, close to the connector.

Reinhard


Re: TEK 465 S/N>25000 Power Supply Issue

Craig Cramb
 

Oran,

Thanks for starting this discussion.
Here are the values you were asking about.
When everything is connected, what voltages do you see:
At 15V TP. 1.675vdc
At the emitter of Q1546. 1.683vdc
At the base of Q1546. 2.223vdc
pin 7 of U1524B 2.988vdc
base of Q1548B. 2.084vdc
Voltage across R1549 (this tells us how much current is pulled from Q1546). 0.008vdc

We are looking for a possible high current out of U1524B pin 7 (~ 10mA).

Craig


Re: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe

Tom Lee
 

The 7B92A (and NOT the 7B92) was indeed a masterpiece, brought to us by the eminent Bruce Hofer. He broke with the longstanding Tek tradition of a Miller integrator for generating the sweep and thereby solved many tough problems in one fell swoop. The non-A version marks the end of the old way of doing things. I thought my non-A timebases were all out of whack, but after studying the circuits, I realized that they were working as well as they could. It’s a great tutorial example of the limits of a Miller integrator.

Tom

Sent from my iThing, so please forgive typos and brevity.

On Feb 7, 2021, at 1:59 PM, n49ex via groups.io <n49ex=aol.com@groups.io> wrote:

No sense hunting around all over. I would suggest go to the 7B92's connector in the back and directly check the power pins to ground. They are on the A connector side: +50 net pin 19, +15 net pin 18 (and it's most likely short C972), +5 lights pin 9, +5 pin 8; on the B side pin 18 is -15 (with it's most likely C976). Once you identify the shorted supply there (something in the few ohms or less region), THEN start chasing it down on that power net. Schematic and full maintenance manual is on TEkWiki http://w140.com/smb/7b92a_sm.pdf

I've always thought the 7B92A was an absolute design masterpiece when you think about how much functionality they crammed into this space (for the time), and the astonishing analog triggering performance. One of my all time favorite Tek accomplishments, right up there with the (7904) distributed delay line CRT deflection system - and the roadrunner meep-meep cartoon on the first edition manual schematic of the vertical output!

Reinhard





Re: TEK 465 S/N>25000 Power Supply Issue

Ozan
 

Hello,
I don't have a 465 but I briefly looked at the power supply schematic on sheet <12>.

Started trying to determine the possible issue and determined that I had no
+22vdc at U1524A&B input.
If this is the +22V at pin 8, it is needed for both 55V and 15V regulators.

So continued on going thru the +55 regulator and
determined that if I left pin 1 out of the U1524 base socket the +22 vdc would
show up.
This would disconnect +55V regulator feedback loop, without the feedback loop I expect +55V to rise to an out of spec voltage (not safe). I don't recommend disconnecting pin 1. I can't easily explain why +22V would show up, may be R1524 now supplies more current (see below).

So then re-socketed the pin 1 along with all others and it would drop
+22 again to 2.26Vdc. So I moved to the B section of chip U1524 and removed
pin 7 with all the others in the socket the +55 V would go to 54.9vdc.
What was the voltage at +22V when you disconnected pin 7? If it recovered to +22V you have either a short in +15V supply or a bad transistor Q1548. This is the theory of what is happening: If output of U1524B is pulled to ground it takes current from its supply (pin 8) which comes from +22V. This voltage is generated by R1524/VR1526 shunt regulator. It can't supply current above (55V-22V)/4.7k=7mA without going out of regulation.

Traced it down to the Q1544 transistor when it was removed the U1524 amplifier voltages
would come up to as the markings in the manual for voltages except for the
lead 6 of the U1524B.
Removing Q1544 cuts the current to +15V and also turns off Q1548. The issue still points to either a shorted +15V or bad Q1548. Lead 6 of U1524B is +15V supply, without Q1544 +15V can't regulate so it is normal to have lead 6 ~ 0V in this condition.

Swapped it out the Q1544 with no change. So now if I
just disconnect the base of transistor Q1544 +55 and voltage readings around
the U1524 a&b are as needed along with the +55.
I assume in this state +15V TP is ~ 0V

Thinking that the Q1546 is
causing the issue. As I have basically gone thru and checked all the
resistors, capacitors and diodes involved in the circuit down to the TP1548
+15VDC. Including the Q1546 and don't see any issue.
I also think you are looking at the correct area.

When everything is connected, what voltages do you see:
At 15V TP
At the emitter of Q1546
At the base of Q1546
pin 7 of U1524B
base of Q1548B
Voltage across R1549 (this tells us how much current is pulled from Q1546).

We are looking for a possible high current out of U1524B pin 7 (~ 10mA).

Ozan


Re: 576 serials

Mlynch001
 

Occasionally, the S/N is also written with black marker on the inside of the case or on one of the circuit boards.
--
Michael Lynch
Dardanelle, AR


Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Ed Breya
 

Hi Attilio,

Yes, keep your new crystal (52.5 MHz) in place from now on. For the first test, you want the setup you already were using at some point before, with the counter in high band, looking at the IF output, where it previously showed the LO frequency, and with the LO running from +15 V, which was the limit of your external supply, as I understand. This should show something around 2095 MHz on the counter, as before. The PLL should be running open loop without any IF feedback, which is what you want. Then you want to confirm that the PLL tune output voltage can rise and stay at somewhere around +17 V, which is about where I think it should go when open-loop. But, if the search oscillator kicks in, then it will need to be disabled. If all goes well, the tune voltage will go up and stay near 17 V.

Presuming the first test works as planned, the next step is to remove the external supply, and reconnect the internal tune voltage via P446, so now the LO is running near 17 V, and should be at a higher frequency, which should show on the counter. That tells you how high it can go without additional modifications, and it's hopefully well over the 2095 MHz result at 15 V. If it is, then there's a very good chance that when you close the PLL loop, it will run the LO up to the desired 2095 MHz and lock, and the tune voltage should end up somewhere near 15 V (where you got about 2095 MHz before), and be stable.

The last test finally closes the loop by restoring everything to normal - putting the 2LO in from the 7L13, connecting the IF out to the PLL, and enabling the search oscillator. Now you're looking for a stable tune voltage around that 15 V, which would show that the PLL is in control, and the LO should be locked at 2095 MHz. The counter isn't necessary, but you can measure the IF if you want, with the scope probe and counter setup as you did before, tapping into the IF amplifier signal, but be sure to not interrupt the IF to the PLL.The IF should be at the new 105 MHz, or at 52.5 MHz after the divide by two circuit. Now everything should be running about right, if the 2LO BPF isn't so far out of adjustment that there's not enough signal to get a good IF level.

In reality, you could skip the first test, but it's good to start from a stable point you know, where you had it set up and measuring the LO frequency. Also, if the tune voltage driver does not operate as I expect, then that issue would need to be addressed before the next steps can work..Good luck.

Ed


Re: 576 serials

cnc_joker
 

Thanks, I can see where the sticker was, only the stickum is left.


Re: 576 serials

Michael W. Lynch
 

On Sun, Feb 7, 2021 at 08:54 AM, cnc_joker wrote:


i also have a 176 plug in, does that have
a serial number? I could not find one.
There should be a standard TEKTRONIX Serial # label on the 176. The one that I saw had this decal on the center of the lower front panel. See Tekwiki140 for a picture. Perhaps it has been removed?

--
Michael Lynch
Dardanelle, AR

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