Date   
Re: 7L5 dot frequency reset bug - any clues or a fix?

Dave Casey
 

My late 7L5 (B09...) powers up in my 7854 at various frequencies. Also
sometimes it powers up in 10dB LOG mode and other times in LIN mode. I
powered it off and on a few times (with varying off times) and observed the
following:
1266.75KHz, LOG
2000.00KHz, LIN
3777.25KHz, LIN
3767.25KHz, LOG
3795.00KHz, LOG
Sometimes I tuned it down to zero before power cycling, sometimes I didn't.

This 7L5/7854 combo has the known readout bug, and this 7L5 has not been
modified for the 7854 CHOP mode issue.
I have another 7L5 I can dig out to test, but I would expect to see similar
results.

Dave Casey

On Sun, Dec 8, 2019 at 1:09 PM Cliff Carrie <cliffcarrie@...> wrote:

At 7L5 SN B060000 Tek changed U830 from PN 155-0117-00 to 155-0198-00.
This may be a reset bug fix, but I have not found any Tek info on it. Also,
there is a typo in Diagram 8. U830 shows as PN 155-0177-00. The parts list
(and my 7L5) show 155-0117-00.



Re: repairing a 184

Eric
 

Bill, I have a working 184 if you need me to take some high rez pictures for you let me know I am pretty sure mine has not been tampered with.

Re: 577 AC collector supply not reading zero on display

DW
 

I tried a few things in hopes to resolve the collector supply which seems to be partially on.

I cleaned the contact wiper points as they seemed slightly dirty on the auto transformer and wiper with fine sand paper then wiped it with some cotton swabs tipped in 92% alcohol to clean the surface.

I turned on the instrument and the results are still the same.

I put one probe on ground and the other on R101, which I believe is in circuit with the wiper of the auto transformer T101, I measured the AC voltage. Turned full on it measures line voltage and turned all the way off about 11 VAC, I believe I definitely found where my undesired leakage power is coming from in the collector supply.

Can these auto transformers go bad?

Re: repairing a 184

bill K7WXW
 

On Sun, Dec 8, 2019 at 01:14 PM, Tom Gardner wrote:


The manual states, p 3-2 col1, "The resultant output markers from the emitter
of A123 are delayed by approx 76us by delay line L123 to allow stacking with
other selected time markers.".

You can select more than one time marker simultaneously, e.g. if you press the
1us and 10us buttons simultaneously then every tenth marker is of a higher
amplitude.
Thanks Tom. I read that section at least three times and missed the last sentence every single time. Going to read the whole thing again and see if I missed answers to other questions. If not, hoping others here will have some ideas.

Re: repairing a 184

Tom Gardner
 

On 08/12/19 20:57, bill K7WXW wrote:
I have a 184 that partially works: the 10MHz signals along the 10HMz, 100MHz, and 200MHz, and 500MHz. The problems are in the 1us and 5us chain. Among other things, there is some poorly done rework in this part of the circuit, the ferrite beads shown on the schematic (input and output side of the delay line) are gone, there are some questionable transistor and part substitutions.

But this is my first 184, so I don't know what a "good" one looks like. Perhaps someone that has worked on one can tell me:

What is the purpose of the delay lines on the 0.5us and 1.0us marker lines?
The manual states, p 3-2 col1, "The resultant output markers from the emitter of A123 are delayed by approx 76us by delay line L123 to allow stacking with other selected time markers.".

You can select more than one time marker simultaneously, e.g. if you press the 1us and 10us buttons simultaneously then every tenth marker is of a higher amplitude.

repairing a 184

bill K7WXW
 

I have a 184 that partially works: the 10MHz signals along the 10HMz, 100MHz, and 200MHz, and 500MHz. The problems are in the 1us and 5us chain. Among other things, there is some poorly done rework in this part of the circuit, the ferrite beads shown on the schematic (input and output side of the delay line) are gone, there are some questionable transistor and part substitutions.

But this is my first 184, so I don't know what a "good" one looks like. Perhaps someone that has worked on one can tell me:

What is the purpose of the delay lines on the 0.5us and 1.0us marker lines?

The ferrite beads on the input and the delay line seem to be in other gear, too, and listed as 0.6uH. In the schematic, they look like they are wound as a transformer with the secondary tied to ground at both ends. Anyone know a substitute part and how they were wound?

The delay line looks like it has been mucked with, too. Is there a better way of testing it than putting a pulse into it and measuring the delay to see if it matches?

There is a lot of 10MHz signal appearing on the trigger output, especially when the the marker is set to 0.1us, and some marker edges appearing in the trigger output at other mark rates. I noticed that the 12V rail in the two buffer amps at the trigger and marker outputs is tied together through a resistor and that the voltage is changing with the marker. That shouldn't be happening, should it?

I am trying to get the unit back to its schematic form and address the crosstalk issues. Any help with these questions is much appreciated. 73 Bill

Re: DC-508 repair advice

radioconnection@...
 

Looking at U1660 I am seeing a good gate signal on pin 5, good signal level on pin 9, but nothing on the Q output from pin 15... I don't have the truth table handy, but the R input on pin 4 is being held low. Q output pin 2 always high. Sound like a bad ECL chip?

Re: 7854's for sale

Fred S.
 

Hi,
would you consider just selling the computer boards, I need an A29 display board for my 7854.

--
Best regards,

Fred S.

Re: 7L5 dot frequency reset bug - any clues or a fix?

Cliff Carrie
 

At 7L5 SN B060000 Tek changed U830 from PN 155-0117-00 to 155-0198-00. This may be a reset bug fix, but I have not found any Tek info on it. Also, there is a typo in Diagram 8. U830 shows as PN 155-0177-00. The parts list (and my 7L5) show 155-0117-00.

Re: Trying to save a 576

Miguel Work
 

The last tube crt monitor tube that I fixed was using a 576 as cathode bias power supply. ;)

Some examples in crt tube restorantion:

http://www.ke5fx.com/crt.html



-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Kurt Swanson
Enviado el: domingo, 8 de diciembre de 2019 18:43
Para: TekScopes@groups.io
Asunto: Re: [TekScopes] Trying to save a 576

Eric,
I've had real good luck restoring cathode emission in TEK manufactured CRTs. A number of testers intended for the TV repair market can do this: the gold standard is the Sencore CR7000, but the Sencore CR70, as well as testers from Beltron, Heathkit, etc. also work well. You want the type of tester that uses a current limited supply to pull current between the cathode and G1 of the CRT, not the type of tester that applies a high energy pulse to the cathode. The current limited type of operation is usually referred to as cleaning or restoration as opposed to rejuvenation. Scope tubes, with their small structures, call for careful work with short duration, but I've had close to 100% success, including tubes that were so dim the trace could barely be seen in a totally dark room.

This process takes some finesse, so I would not start learning on a precious tube - If you happen to know anyone who used to work on CRT TVs, or someone who is into arcade games, they may be able to help, or point you to someone who can.

Good luck here. Bottom line: this technique is always worth trying on a weak tube - after all, you have nothing to lose.

Regards - Kurt

Re: Tek 3c66 Carrier Amplifier Bridge plug-in for the Tek 560 series scope

garp66
 

hi Tim,

I found a report that described the use of( & with schematics) the Tek 3c66 AC Carrier Bridge Amp plug-in (in a Tek 564b) with a conductivity sensor.
Very well described:
Environmental Protection Agency report EPA-R2-72-053 November, 1972.

rick

Re: Yet another 7L5 issue (7L5 / 7854) below 10 kHz

Nenad Filipovic
 

Hi Cliff,

Yes, in my opinion the "below 10 kHz" problem is purely on the 7854 side,
as my 7L5 displays CF correctly in both 7633 and 7104. I did not bother
much with it as I simply got used to it, and with GPIB data it is possible
to implement a fix for it in capturing software.

The reset anomaly is also present in mainframes other than 7854. In my 7854
it powers up at 3778kHz most of the time, but not always. In 7104 it does
1788kHz or something similar. I did not get into it deeper as it did not
bother me nearly enough as the very annoying mV issue in LIN mode on 7854.
The last is definitely a 7854 fault.

Is your 7L5 the older (SN below B069999) or the newer version? Mine is the
older. I think I remember I read somewhere that the older version is prone
to the reset problem, but can't say for sure.

Best Regards,
Nenad

On Sun, Dec 8, 2019 at 5:34 PM Cliff Carrie <cliffcarrie@...> wrote:

Nenad,

I too have spent a lot of time on my 7L5, mostly in a complete overhaul of
the front panel hardware bits and correcting some assembly errors from the
last person who took it apart. This hobby is at least as much about
restoring these classic units as it is about using them.

Thanks for the links to your earlier posts. I had read them some time ago.
I can certainly agree that the "below 10 kHz" problem could be in either
the 7L5 or the 7854. I will try to test my 7L5 in a non-7854 7k mainframe.
I have an acquaintance locally who had at least one.

There is a big difference between the two problems, however. In the 10 kHz
problem, the 7l5 is correctly tuned. Only the frequency display is wrong.
In the power on problem, the 7L5 is actually tuned to 3778 kHz instead of
zero. I can't think of any signals inbound from the 7854 to the 7L5 that
can change the tuning. I still hope there may be a 7L5 solution to this
one. I will keep searching.

Cliff

Re: Trying to save a 576

Kurt Swanson
 

Eric,
I've had real good luck restoring cathode emission in TEK manufactured CRTs. A number of testers intended for the TV repair market can do this: the gold standard is the Sencore CR7000, but the Sencore CR70, as well as testers from Beltron, Heathkit, etc. also work well. You want the type of tester that uses a current limited supply to pull current between the cathode and G1 of the CRT, not the type of tester that applies a high energy pulse to the cathode. The current limited type of operation is usually referred to as cleaning or restoration as opposed to rejuvenation. Scope tubes, with their small structures, call for careful work with short duration, but I've had close to 100% success, including tubes that were so dim the trace could barely be seen in a totally dark room.

This process takes some finesse, so I would not start learning on a precious tube - If you happen to know anyone who used to work on CRT TVs, or someone who is into arcade games, they may be able to help, or point you to someone who can.

Good luck here. Bottom line: this technique is always worth trying on a weak tube - after all, you have nothing to lose.

Regards - Kurt

Re: 7L5 early version (SN below B069999) Mod FB for 7854 compatibility

Cliff Carrie
 

Nenad,

I too have spent a lot of time on my 7L5, mostly in a complete overhaul of the front panel hardware bits and correcting some assembly errors from the last person who took it apart. This hobby is at least as much about restoring these classic units as it is about using them.

Thanks for the links to your earlier posts. I had read them some time ago.
I can certainly agree that the "below 10 kHz" problem could be in either the 7L5 or the 7854. I will try to test my 7L5 in a non-7854 7k mainframe. I have an acquaintance locally who had at least one.

There is a big difference between the two problems, however. In the 10 kHz problem, the 7l5 is correctly tuned. Only the frequency display is wrong. In the power on problem, the 7L5 is actually tuned to 3778 kHz instead of zero. I can't think of any signals inbound from the 7854 to the 7L5 that can change the tuning. I still hope there may be a 7L5 solution to this one. I will keep searching.

Cliff

Re: DC-508 repair advice

 

Hi Pete,
I can answer your questions about what the Option 7 is for:
It is used with a TR-502 tracking generator and a TM-503 which has wired interconnections between these two plugins on the TM503 backplane. This DC508/TR502/TM503 combination will then connect to the 7L13 or 7L14 Spectrum Analyzers through a special 6 wire cable with LEMO connectors on each end to measure the exact frequency the 7L13 or 7L14 is tuned to and display it on the DC508 counter. As the spectrum analyzer's trace sweeps across the CRT, it stops momentarily at the midpoint of the CRT long enough for the DC508 to measure the frequency of the TR502 and display it with up to 1Hz precision. Once the DC508 makes the measurement it releases the sweep of the 7L13 or 7L14 to continue. The entire pause only lasts as long as the measurement period of the DC508 which can be anywhere from 1mS to 1S depending on how much resolution you want. The DC508 is capable of measurements up to 1.3GHz although these two SAs go up to 1.8GHz.

I think you are correct about connecting the TR502 Aux Out to the DC508. It's been a while since I used all of this and I am not certain.

It is a very clever combination of several instruments (tracking generator, spectrum analyzer, and frequency counter) making a very difficult and useful measurement if you are working with RF.

Dennis Tillman W7PF

-----Original Message-----
From: radioconnection@...
Sent: Sunday, December 08, 2019 6:29 AM
Subject: [TekScopes] DC-508 repair advice

Hello to the group--not exactly a Scope problem, but I was given a TM-503 that was full of plug ins. There is a 508 counter that does have the preselector daughter board installed.

It is not working. When using the presecaler the input level led shows it is seeing a signal from my HP-8640 signal generator. The gate lamp is flashing. The display leds are blanked until the counter sees a signal, and then the LEDs only show zeros, but no counts. On the direct input the counter also does not count. Gate lamp is flashing. The PLL light goes out when I apply a 1 kHz signal. I am guessing there is something wrong with the gate since the input and timebase seem to be working?

I do not have extender boards and I am very unfamiliar with this counter. I did download a PDF file of the manual, but it is rather cumbersome to use on a computer. Any suggestions where to start?

Also, I've read there is an Option 7 that was intended to use the DC508 with a TR-503? What exactly does that show? The center scan or the exact count as the SA is being swept? The 503 does have an aux. RF out that could be fed to the DC-508, will that do the same function?

Pete




--
Dennis Tillman W7PF
TekScopes Moderator

7854's for sale

demianm_1
 

i have 3 and have decided to move 2 on. They take up space I can no longer afford to support. The 7854's have no plugins and I'm asking $275 ea w/ carts. I also have a 7613 with a 7L12 that i have not used in a long time. Also $275 with cart.
I'm looking for someone local (SF Bay Area) since shipping especially with a cart is prohibitive.
Contact me at demianm_1@... to be sure I see the note.

Re: DC-508 repair advice

Jean-Paul
 

Pete, any old plug-in may have oxidized switch contacts.

My first guess is to exercise and lube all switches.

Often this solves the problem.

DC-508 is a great counter, but the many stacked boards make it difficult to repair.

Extender cables are one solution but you can access most of the plug-in by mounting in a TM 501,2,3 mainframe with covers removed

Good luck


Jon

DC-508 repair advice

radioconnection@...
 

Hello to the group--not exactly a Scope problem, but I was given a TM-503 that was full of plug ins. There is a 508 counter that does have the
preselector daughter board installed.

It is not working. When using the presecaler the input level led shows it is seeing a signal from my HP-8640 signal generator. The gate lamp
is flashing. The display leds are blanked until the counter sees a signal, and then the LEDs only show zeros, but no counts. On the direct
input the counter also does not count. Gate lamp is flashing. The PLL light goes out when I apply a 1 kHz signal. I am guessing there is
something wrong with the gate since the input and timebase seem to be working?

I do not have extender boards and I am very unfamiliar with this counter. I did download a PDF file of the manual, but it is rather cumbersome
to use on a computer. Any suggestions where to start?

Also, I've read there is an Option 7 that was intended to use the DC508 with a TR-503? What exactly does that show? The center scan
or the exact count as the SA is being swept? The 503 does have an aux. RF out that could be fed to the DC-508, will that do the same
function?

Pete

Re: 465 No Horizontal Sweep

david
 

Cap C1220 is wet Tantalum, all caps in 465 are tantalum except for Filter Caps in power supply section. I replaced C1220 with a Aluminum electrolytic, and all is working correctly. Also replaced R1220 which was burned black. All voltage readings in Horizontal Amp section correct except for Collector of Transistor Q1226. Measures -0.36v, should be -0.45v ,20% low, I believe the -0.45v is the forward voltage of Diode CR1253, but scope is working well so I am not concerned. If it's not broke don't fix it.

Re: 7A15A issue or limitation??

Chuck Harris
 

Simple explanation, I think:

"Vertical mode" triggering is only valid when there is
a single vertical signal displayed on the screen, or you
are in ALT (alternate) mode.

It gets more complicated if I try to tell you why:

The only modes where the traces on the screen are exactly
what they appear is when there is only a single channel
displayed on the screen.

Whenever there is more than one channel on the screen,
there is some form of eye trickery going on. This is
because there is only a single beam in the CRT to draw on
the screen. A couple of scope models have multiple beams,
but they are the exception, rather than the rule...

In ALT (alternate) mode, it may appear to the eye that
there are two signals on the screen at the same time, but
in reality, the two signals are being shown singly,
alternating: A, B, A, B... If the sweep time is fast enough,
the eye merges the alternating images so they appear to the
brain to be simultaneous.

At the slower sweeps, the eye can easily see the traces
alternate.

In CHOP (chopped) mode, it may appear to the eye that there
are two signals on the screen at the same time, but in
reality, the two signals are chopped up into alternating
tidbits.... a tidbit of A, a tidbit of B, a tidbit of A, a
tidbit of B...all the while the sweep marches on, making a
sort of square wave with the tops being the tidbits of one
channel, and the bottoms being the tidbits of the other
channel.

Because the chopping of the A and B signals is faster than
the sweep speed, and with no time relationship to the sweep
speed, or the signals, the eye sees the chopped up signal to
have merged into what looks like simultaneous display.

But the trigger isn't a human eye, so it isn't fooled by this
trickery.

When the trigger mode is in "Vertical", the trigger is given
the exact signal the plugin is trying to display on the
screen: Single channel mode, gives the single channel.
Alternate mode, gives an alternation of Channel A and Channel B.
Chop mode gives a composite signal of a little bit of A, B,
and their vertical positions... A real dog's breakfast.

"Vertical mode" triggering is only valid when there is a
single vertical signal displayed on the screen, or you
in ALT (alternate) mode.

-Chuck Harris

tinkera123 wrote:

Hi,

I have been playing around with my 7A15A's, in different 7603 Mainframes, and have a 'jittering' or 'flickering' of the 4V Calibration signal.
The 'jittering' is a movement, always to the left, of the trace along the horizontal axis and return to the correct position.

I can define this issue or limitation as follows:-
Independent of Mainframe - 2 x 7603's used
Independent of Timebases - 7B53 and 7B92A used
Only occurs in TRIG SOURCE/VERT MODE with VERT MODE/ALT - both traces are stable in all other Modes
Only one of the traces becomes unstable
Only occurs when traces from each Vert Amp are 'un-overlapped' - when the two traces are overlapped, both traces are stable

The Manual states that in TRIG SOURCE/VERT MODE .... "each sweep is triggered by the signal being displayed on the CRT"

This suggests to me that when I dive into the Circuit Descriptions, that I should be looking for some 'switching mechanism' which is swapping the Triggering mechanism between the signals from each Vert Amp.
If this 'switching mechanism' is faulty or receiving a weak signal, then this maybe causing poor triggering, hence the 'jittering'.
However, this 'switching' between Vert Amp signals would occur in the Timebase or Mainframe.
But that doesn't make sense because the 'jittering' occurs in both 7A15A's, independently (ie. 7A15A + 7A26 + 7B92A etc), and in 2 different Mainframes, and with different Timebases.
So .... where have I gone wrong here???? ..... or is this a limitation of the 7A15A???

Any guidance is appreciated.