Date   

Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio
 

Hi Ian,
I will be very careful not to damage the first mixer of my 7L13, I thought in any case to insert a DC blocker with a blocking capacitor of 1000 pF and two diodes in anti parallel. I have some HP5082-2835 diodes, can
I use them ?

Greetings to all
Attilio


Re: Yet another 'replacing carbon resistors with metal film' question....

 

Personally I would *only* replace CC resistors that were causing out of specification behaviour. If e.g. all resistors in a potential divider have drifted high by the same %age (as is probable) then the divider will still have the correct voltages.

Or put another way if you can calibrate it successfully, then don’t replace anything at all!

David

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jared Cabot via groups.io
Sent: 28 December 2020 09:47
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yet another 'replacing carbon resistors with metal film' question....

Yeah, I'll be recalibrating for sure, as I intend to use it to calibrate other gear.

I'll test things thoroughly and might do as you say, just replace what is needed. I already tested the capacitors as perfect so they are back in place to continue being used.
I was just thinking to replace all the carbon composite resistors now as they are a known failure point and failures have already started. I just wanted to avoid having to go back in later and end up having to recalibrate etc multiple times.

It looks like Digikey stock carbon composition resistors too, so maybe I should swap like for like for those that are out of spec?


Re: Tektronix 1A7 and 1A7A Plug-ins

um-gs@...
 

Hi Dave,
today I gave my 1A7 (and the manual) a thorough look and found that there is indeed not a dual-Nuvistor pre-amp installed (as the manual says) but instead a PCB which obviously holds different parts (dual FETs?). The PCB is marked "1334XA".
As you mentioned 15 years ago in the above the "field-installable kit" - that might the be the explanation.
Do you by any chance have more references to this kit (and the schematic)?

Regards, Gordian


Re: Yet another 'replacing carbon resistors with metal film' question....

Jared Cabot
 

Yeah, I'll be recalibrating for sure, as I intend to use it to calibrate other gear.

I'll test things thoroughly and might do as you say, just replace what is needed. I already tested the capacitors as perfect so they are back in place to continue being used.
I was just thinking to replace all the carbon composite resistors now as they are a known failure point and failures have already started. I just wanted to avoid having to go back in later and end up having to recalibrate etc multiple times.

It looks like Digikey stock carbon composition resistors too, so maybe I should swap like for like for those that are out of spec?


Re: Yet another 'replacing carbon resistors with metal film' question....

Jean-Paul
 

Mr Cabot: We have PG501, 502, 506, running perfectly with all original parts, needing some switch and pot cleaning on occasion.

Carbon comp are lower self capacitance, and are still used in critical high freq and high voltage applications.

If it needs service, I suggest to replace ONLY failed/out of spec parts causing the issues, and leave all other parts alone.

Most of the changes in resistor type will make no difference.

"if it ain't broke dont fix it"

Regardless I suggest recalibration afterwards.

Bon chance,

Jon


Yet another 'replacing carbon resistors with metal film' question....

Jared Cabot
 

Hi all,

I have a PG502 TM500 module here I'm poking away at, and although the capacitors all test better than the datasheets in all respects (Those Vishay 30D caps are pretty good!), some of the old brown square ended carbon composite resistors have predictably drifted.
I also found also that the 15V trimpot is high resistance unless you press on the dial leading to no voltage rails, so that will be replaced.

I want to replace all of the fixed carbon composite with new resistors, but I'm not sure which way to go...
I have a set of modern 5% carbon film resistors, and also a set of 50ppm 1% metal film resistors too. I'm not too worried about using film resistors on the power supply etc, but the rest of the circuit is what I'm not sure about. I assume in this situation, the metal film is better than the carbon film seeing as they are both spiral cut?

What's the rule of thumb here? Should I just shotgun the metal film resistors and hope for the best, or use carbon composition resistors instead?

Here's the data sheets of the resistors I have:

Carbon film: http://takman-e.co.jp/pdf/rd_rds.pdf
Metal film: http://takman-e.co.jp/pdf/rlc.pdf


Re: Tek 465 Negative 8 volt rail issues

Dave Peterson
 

Paul,

I'm putting together a Mouser project for 465 PS caps. I pulled all 5 as they appear to have been leaking, it was going to be necessary to get at the suspected C1513, and once I got going it wasn't that bad, so might as well do all of them. I also have the adapter boards ordered and waiting for USPS to get them across country.

I was searching for radial Nichicon caps as I'm pretty happy with the order I made for C1419 replacements. I didn't catch your earlier reference to "snap" caps, and I see that these come in higher capacitance and voltage values than radial. Not that radial's aren't available, it just appears snap caps are inherently larger?

I've never heard of snap caps before. Aside from the obvious lead difference, what is the purpose/difference between radial lead caps and snap caps?

Dave


Re: 1S1: Defect trigger functionality repair

Glenn Little
 

Mine does not work.

Glenn

On 12/27/2020 10:09 PM, snapdiode via groups.io wrote:
Can I borrow your curve tracer? I mean after the pandemic.



--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"


Re: need case for 067-0508-00 Amplitude Calibrator

cougar_lou
 

Rick and the group.I have that rack assembly with the 184 and the amplitude calibrator.It is 110/220 Volt switch selectableUnfortunately,I'm currently 650kms from home visiting my daughter so I can not give you the type number from the name plate,I will be back home next week and will recontact you then.
Best wishes,Brian g


Re: 1S1: Defect trigger functionality repair

snapdiode
 

Can I borrow your curve tracer? I mean after the pandemic.


Re: 465 Scope AC Gnd DC Coupling Switch

JJ
 

Hi Dave,
Wow! I thought removing and repairing my 7904's power supply was tough!
This really sounds tricky. I'll need to spend a day or so going through the
465 service manual.
Thanks for the terrific detail, I'll be referring to it as I move along.
Pictures would be great!
I won't be getting to the 465 for a few days, I'm in the process of chasing
down signals in my Carver stereo receiver that I purchased new some 35
years ago. I just saw that the big filter caps that I need to replace are
glued down to the PC board! What Fun!
Thanks again.
Best,
John


Re: 1S1: Defect trigger functionality repair

Tom Lee
 

Thank goodness the Russians produced so many TDs back in the day! I like their tiny CRTs, too.

In case the TD supply ever dries up, it might be helpful to know that it is possible in a surprising fraction of cases to heal a bad TD. Throw it on a curve tracer and crank up the current to the upper edge of the allowable dissipation so that the TD self-heats significantly. Watch the valley current -- it should go down as self-annealing works its magic. Once it gets to where it should be, you can stop (although I generally keep current through it for another minute or so). Let it cool to room temp and test again. Repeat if and as necessary.

The same low activation energy that makes the TD drift with age also makes it possible to anneal them this way.

-- 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 12/27/2020 14:15, um-gs@arcor.de wrote:
There have been quite some discussions about missing posts regarding the fabulous Tek 500 series...https://groups.io/g/TekScopes/message/175302 ... to show that the matter is still alive, here a recent repair of an 1S1 Sampling plug-in (in a 547), where the triggering function did not work.
Symptoms:
- the plugin produced a vertical/horizontal signal
- internal triggering did not produce a stable display
- a large (0.5V) signal at the external trig input produced a stable display
Circuit check:
- Moving the Trigger Sensitivity didn't change anything
- calibration step 4: adjustment of internal trigger level: no effect when adjusting R420 (trace still free-running)
- calibration step 5: also no adjustment with R460 possible meeting the cal instruction
- changing trigger sensitivity pot and/or R420: No change in current through (voltage drop across) R440
- junction D430/R444 remained at near zero volts
Conclusion:
Defective tunnel diode D430
Repair:
Replacing D430 with a type 3I201B (Russion production) - restored full trigger capability.
These tunnel diodes are available on ebay for very reasonable prices

Cheers, Gordian




Re: PG506 calibrator generator voltage error

Harvey White
 

If you have all of those, and more than one 7000 series mainframe, you may want to look at the standardizer plugins for the 7000 series.

They put out a standard set of waveforms/voltages and replace a plugin.  They allow you to standardize the input sensitivity of a 7000 series scope (they have gain controls on the input channels *in the mainframe* which need to be adjusted *if* you have more than one frame and *if* you want the plugins to be calibrated once they're plugged in.  If you only have one 7000 series frame, then in a sense, you calibrate the plugins to that so they're all correct, and you have no other frame to transplant the plugins to.

Be aware that the standardizers come in different varieties (check last digits in the type name) for different bandwidth scopes.  They can be used in either the V or H channels (using one in each with the right settings gives you a grid).  One other ability they have is to be able to convert a variable amplitude (as in.... not constant amplitude) signal to a constant amplitude signal.  I suspect that the different plugins have different frequency ranges for the sinewave input.  If you have  a constant amplitude signal generator, you don't need that feature.  Setting the input signal amplitude can be a bit tricky, though.

A lower bandwidth plugin can do most of what you'd want for the frame, but you can't check the bandwidth of the frame completely with a lower bandwidth plugin.

Harvey

On 12/27/2020 7:24 PM, Gif Sim via groups.io wrote:
hi thomas
Thank you for your contribution
you're right ..... I was very superficial in describing the "noise" I see with the scope
tomorrow I will upload some screenshots of the oscilloscope and some info on the settings of the pg508a and tds784d
here in Italy it is midnight .... I was late tonight ..... I ate now .... I go to sleep
the pg506a is really a very useful plug-in .... I use it a lot .... I have the whole series pg506A-tg501A-sg503-sg504
bye
simon





Re: 1S1: Defect trigger functionality repair

snapdiode
 

Great news. This means the 3I201B can replace Tek # 152-0177-00 (TD253B 10 mA). At least in a 1S1.


Re: PG506 calibrator generator voltage error

Gif Sim
 

hi thomas
Thank you for your contribution
you're right ..... I was very superficial in describing the "noise" I see with the scope
tomorrow I will upload some screenshots of the oscilloscope and some info on the settings of the pg508a and tds784d
here in Italy it is midnight .... I was late tonight ..... I ate now .... I go to sleep
the pg506a is really a very useful plug-in .... I use it a lot .... I have the whole series pg506A-tg501A-sg503-sg504
bye
simon


Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

tinkera123
 

Hi Attilio, re Diodes in DC Block .... I am away from Home at the moment and have very limited internet ... search something like "DC block, spectrum analyzer" and you should get plenty of hits. You could get technical with types of different diodes, but as per advice above, one still needs to be careful.

--
Cheers,
Ian,
Melbourne, Australia


Re: PG506 calibrator generator voltage error

Tom Lee
 

Ceramic caps rarely become defective from simple age, but can be damaged, as can any other component. For example, if a previous user connected the PG506 to something whose common-mode voltage was very greatly different, that cap could've suffered.

You haven't described the noise in any specific detail, so your question can't be answered in any specific detail. Generally speaking, verify that your supplies are clean. And try to provide more information if you want to get more helpful responses. Is the noise manifesting as timing jitter? Amplitude noise on the flat portions? Does the noise appear to have structure? etc. The more you can tell us, the more we can tell you. And in the process of finding more yourself, you will frequently be led to the problem's cause on your own.

Congratulations on getting this far.  I'm sure you'll find that plug-in a very useful tool!

-- 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 12/27/2020 14:29, Gif Sim via groups.io wrote:
yess ... yesss .... it was c100 now the pg506a works correctly !!!!

never happened that a ceramic did so '... usually electrolytic and tantalum give problems
I hope it will be useful to someone .... before writing here I searched a lot on the net but I didn't find much ...

is it normal for Q290 and Q190 to be very very hot?
is there a way to make the output less noisy?
in standard amplitude on 1 Mohm oscilloscope I measure 2 mV P-P
is this a normal value?

THANKS GUYS !!!!!!!!!..........IT'S ALSO THANKS TO YOU !!!!!!!!!

Simon




Re: 465 Scope AC Gnd DC Coupling Switch

Dave Peterson
 

John,
I'll chime in:

I'm new to the 465 world of repair myself, but do have some experience in electronics. I understand the trepidation of digging into your scope. Despite being pretty comfortable with a soldering iron I didn't feel like it was a small thing going into it. Bottom line is there is no way to remove the vertical assembly without some soldering iron work. That said, it's not bad. I'll leave it to you to decide how invested you're into taking a soldering iron to it.

Before beginning review the "Vertical Preamp Assembly Removal" section of the 465 Service Manual in the "Maintenance" section. Between the circuit description and calibration sections.

The key thing that enabled removal for me was that only C3 (CH1) and C53 (CH2) need be removed from the attenuator assemblies to access the 1/4 inch nuts behind them. Everything else is pretty straight forward.

There's a small ground strap on the bottom on the A9 board, and disconnection of the small red wire and the delay line toward the rear of the scope are also needed. I suspect the assembly could be pulled away enough without disconnecting them, but once you have the iron ready you might as well. The delay line is soldered to the board by one of the shield pins. The other pins of the delay line are plug-in and do not need to be unsoldered.

The ground strap on the bottom is between two push-button push rods for INVERT and BEAM FINDER. I removed those so I wouldn't touch them with the hot soldering iron.

I was able to disassemble C3/C53 and the delay line shield with solder wick. For C3/C53 (these are under the attenuator shields) there is one connection to R1, C1, and C2 that's the bundle of leads all soldered together. After wicking the majority of the solder away it was easy to use tweezers and the soldering iron to separate R3 from the bundle. (same goes for CH2). The other side of C3 is connected to tiny 1/4w (or 1/8w?) R3 and is easy to separate. The capacitor body is mounted to the board via a plug-in lead. It just lifts out after unsoldering the two electrical leads. You may notice the cap pivoting on this plug-in lead as you disconnect the R1/C1/C2 bundle.

The delay line shield also responds well to wicking of the majority of the solder first. Then a small pair of tweezers or pliers pulling away from the board while holding the iron to the soldered shield will release it.

I took extensive pictures while doing all this to keep all the connections straight. All other mechanical connections are per the procedure in the manual, and are pretty obvious. The entirety of A1, A2, A3, and A4 come out as an assembly. The CH1/CH2 BNCs and associated 10x components come out with the assembly. Oh, right, there's two signal wires for CH1/CH2 10x lights at the CH1/CH2 attenuators. Those have to be disconnected too.

I haven't posted pictures yet, but have them saved off. I could send key ones if that helps. Let me know if there are any questions, I'll try to help.

Dave


Re: PG506 calibrator generator voltage error

Gif Sim
 

yess ... yesss .... it was c100 now the pg506a works correctly !!!!

never happened that a ceramic did so '... usually electrolytic and tantalum give problems
I hope it will be useful to someone .... before writing here I searched a lot on the net but I didn't find much ...

is it normal for Q290 and Q190 to be very very hot?
is there a way to make the output less noisy?
in standard amplitude on 1 Mohm oscilloscope I measure 2 mV P-P
is this a normal value?

THANKS GUYS !!!!!!!!!..........IT'S ALSO THANKS TO YOU !!!!!!!!!

Simon


1S1: Defect trigger functionality repair

um-gs@...
 

There have been quite some discussions about missing posts regarding the fabulous Tek 500 series...https://groups.io/g/TekScopes/message/175302 ... to show that the matter is still alive, here a recent repair of an 1S1 Sampling plug-in (in a 547), where the triggering function did not work.
Symptoms:
- the plugin produced a vertical/horizontal signal
- internal triggering did not produce a stable display
- a large (0.5V) signal at the external trig input produced a stable display
Circuit check:
- Moving the Trigger Sensitivity didn't change anything
- calibration step 4: adjustment of internal trigger level: no effect when adjusting R420 (trace still free-running)
- calibration step 5: also no adjustment with R460 possible meeting the cal instruction
- changing trigger sensitivity pot and/or R420: No change in current through (voltage drop across) R440
- junction D430/R444 remained at near zero volts
Conclusion:
Defective tunnel diode D430
Repair:
Replacing D430 with a type 3I201B (Russion production) - restored full trigger capability.
These tunnel diodes are available on ebay for very reasonable prices

Cheers, Gordian

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