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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


Re: 465 Scope AC Gnd DC Coupling Switch

JJ
 

OK. Thanks for the heads up. It is mechanical, the coupling switch on the
other channel works fine.
Best,
John


Re: PG506 calibrator generator voltage error

Gif Sim
 

harvey
it's a PG 506A has no relay .....
I removed and measured C100 .... I measure 10-11kohm ... instead it should be a common 100 nF ceramic....
replaced with a new capacitor ... now between the two masses I measure about 2.5 Mohm ..... it seems okkkk !!!
give me some time ... I reassemble the pg 506A .... and I can tell you if it works .... I cross my fingers !!! .........


Re: PG506 calibrator generator voltage error

Harvey White
 

I just leafed through the schematic, and don't see a capacitor between the two grounds (there are, but they're very small values, like 0.01 uf).  What I'd do is to disconnect the relay board, which should isolate the power supply.  I'd check to see if the resistance you see goes away (I'd expect that the normal behavior is very high resistance between grounds.  There *is* a diode (CR67, I think) between the 5 volt (referred to ground) and isolated ground.  I'd wonder about that.  )

Then I'd check between the two grounds again and see which section has the odd reading.

If you want, I could check one of mine to see if it's behaving itself.

Harvey

On 12/27/2020 3:26 PM, Gif Sim via groups.io wrote:
hi harvey
that's exactly what I think too !!
in fact if I connect an oscilloscope isolated from the mains power supply (battery powered) the pg506 works correctly ....
only that inside the pg506 it's a nice mess !! .....
simon





Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio
 

Hi Thomas,
not having this source of noise in my hand, I did not understand how it works, in theory if I connect it to the input of my SA and select MAX SPAN it should come out a more or less horizontal line from about 200 kHz to 1.8 GHz set to a RF level that I still don't understand (maybe 0 dBm?).

Greetings
Attilio


Re: 465 Scope AC Gnd DC Coupling Switch

Ananda
 

I am assuming you have just 1 of them stuck. If you remove the cover and also remove the shield on the vertical amp of that channel, you will be able to see the contacts operated by that switch. Make sure they are not bent in someway which is highly unlikely anyway. Beyond that, it seems like a mechanical problem to me. Getting to that involves removing the vertical board out of the scope which takes some doing. There is good info in the service manual on how to go about it but there are also people on this board who have done this. In my case, the only time I had to fix one of them it did not involve pulling the board out. I am sure one of the experts will chime in soon. You might have to wait since it is the holiday weekend.


Re: PG506 calibrator generator voltage error

Gif Sim
 

hi harvey
that's exactly what I think too !!
in fact if I connect an oscilloscope isolated from the mains power supply (battery powered) the pg506 works correctly ....
only that inside the pg506 it's a nice mess !! .....
simon


Re: PG506 calibrator generator voltage error

Gif Sim
 

hi jon
yes ... that's one of the first things I checked
the grounding of the instruments and the bench are ok ..
i also opened the tm504 to check the ground and a couple of resistors connecting the ground ... all ok
the pg506 has two floating masses .... at this moment I have the pg506 on the bench
if I measure the resistance between the two masses I read 10-11 kohm
I think it's not correct ... Eric has just measured an infinite value between the two masses on a working pg 506 .....
I performed the measurement between the two masses on C100 ....


Re: PG506 calibrator generator voltage error

Harvey White
 

What it sounds like is that something (likely a capacitor) *may* be shorted.  That one capacitor that charges might be bad, so I'd wonder if the sneak path for grounding through the power line is not shorting out something, like for instance, the 120 adjust control?  Now I don't mean that the control is shorted out, but the ground that used to be ground isn't any more, and that throws off the circuit.

Harvey

On 12/27/2020 2:37 PM, Gif Sim via groups.io wrote:
hi bob
thanks for the tips I'll go check it out immediately!
as i wrote to eric i have a pg506a there are no relays ...
the thing I don't understand is that if I connect a battery powered oscilloscope everything works correctly ... all controls and values are normal
i noticed that q290 q190 and r190 are very very hot but taking them apart and trying them they are okk ... also vr210 is ok the 9v are present
I noticed that when I connect an oscilloscope that can be tds784d or 2465b, then powered by the mains
the voltage +120 volts (which I measure on cr291) rises to +125 volts .....
I'm going crazy !!!
thank you all
simon





Re: Tek 453A

Dave Wise
 

?I had the bad HV cap. I fixed it. Then the transformer failed. I rewound it. If the candidate scope has both faults, you'd better enjoy fixing.


Note: I got that 453 for free. Thanks Rolynn!


Dave Wise

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Glenn Little via groups.io <glennmaillist=bellsouth.net@groups.io>
Sent: Sunday, December 27, 2020 6:52 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 453A

My first 453 had no trace.
The fault was a 500 pF filter capacitor on the HV line.
The capacitor was a red, possibly epoxy, encased capacitor.
When held up to the light you could see black arc marks inside the
capacitor,
I replaced the capacitor with a ceramic one and have had no problems since.
I have found this to be the cause of no trace on a few scopes.

If the price is right, the repair may be simple.

Glenn

On 12/26/2020 11:57 PM, Maurice Smulders wrote:
I can obtain a Tek 453A locally, but it doesn't show a trace, so I have no idea yet what is broken. What would be a good offer for it, and is it usually repairable?

- Maurice




--
-----------------------------------------------------------------------
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: PG506 calibrator generator voltage error

Jean-Paul
 

Are you sure of the grounds and mains power connector, could it be a grounding or loop issue?

jon


Re: PG506 calibrator generator voltage error

Gif Sim
 

thanks eric !
what main frame do you use to power the pg506? (I think one of the tm500 series)
can you do the same test with the pg506 inserted in the tm500 and the multimeter connected between the mass of the standard out female bnc and the mass present in the power plug of the tm500?
I think the problem is here .... in my I measure 10kohm ....
thanks
simon


Re: PG506 calibrator generator voltage error

Gif Sim
 

hi bob
thanks for the tips I'll go check it out immediately!
as i wrote to eric i have a pg506a there are no relays ...
the thing I don't understand is that if I connect a battery powered oscilloscope everything works correctly ... all controls and values are normal
i noticed that q290 q190 and r190 are very very hot but taking them apart and trying them they are okk ... also vr210 is ok the 9v are present
I noticed that when I connect an oscilloscope that can be tds784d or 2465b, then powered by the mains
the voltage +120 volts (which I measure on cr291) rises to +125 volts .....
I'm going crazy !!!
thank you all
simon


Re: PG506 calibrator generator voltage error

Eric
 

Hey Simon,
Measured with a Keithly DMM6500 standard output jack to the aluminum frame. In a frame and out of a frame.
In frame, resistance that rapidly went up to overflow. I believe a cap was charging.
Out of a frame, Same behavior.

Once charged infinite resistance.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Gif Sim via groups.io
Sent: Sunday, December 27, 2020 2:10 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] PG506 calibrator generator voltage error

hi eric
yess..I did as you wrote ... the pg506a used it long ago and it was perfectly calibrated and working (I calibrated some 2465b and 2467b)

the strange thing is that if I connect an oscilloscope with 1Mohm input, battery powered, therefore not connected to the mains electricity, to the amplitude standard output, the levels are correct ... the variable out potentiometer works and the display indicates the value set with the pot ....

but if I connect an oscilloscope (such as a tds 784d) with 1Mohm input, powered by the mains electricity, the output voltage is wrong (for example if I set 2 v to the output or about 2.4 v) ... .the variable out potentiometer has no effect on the output voltage and the display indicates a fixed value

my calibrator is the PG506A and one of the latest revisions of the boards there are no relays you find in the first PG506

I checked q325-q365-q326-q320-q280-q290-q245-q255-q270-q190 by removing them from board A1 and trying them with a component test they are all okk...

i checked all diodes and zener on board A1 and they are all okk now i am trying and replacing some electrolytic and tantalum capacitors on board A1 (but so far i haven't found any wrong ones)

Eric can you do me a favor? ... with the PG506 off, set to standard ampl and the selector on 2volt, if you connect the cables of a multimeter between the mass of the standard out female bnc and the aluminum frame of the PG506, what a resistance read the multimeter?

thanks eric and thanks to all those who can give any suggestion to understand the problem!
simon


Re: PG506 calibrator generator voltage error

Gif Sim
 

hi eric
yess..I did as you wrote ... the pg506a used it long ago and it was perfectly calibrated and working (I calibrated some 2465b and 2467b)

the strange thing is that if I connect an oscilloscope with 1Mohm input, battery powered, therefore not connected to the mains electricity, to the amplitude standard output, the levels are correct ... the variable out potentiometer works and the display indicates the value set with the pot ....

but if I connect an oscilloscope (such as a tds 784d) with 1Mohm input, powered by the mains electricity, the output voltage is wrong (for example if I set 2 v to the output or about 2.4 v) ... .the variable out potentiometer has no effect on the output voltage and the display indicates a fixed value

my calibrator is the PG506A and one of the latest revisions of the boards there are no relays you find in the first PG506

I checked q325-q365-q326-q320-q280-q290-q245-q255-q270-q190 by removing them from board A1 and trying them with a component test they are all okk...

i checked all diodes and zener on board A1 and they are all okk
now i am trying and replacing some electrolytic and tantalum capacitors on board A1 (but so far i haven't found any wrong ones)

Eric can you do me a favor? ... with the PG506 off, set to standard ampl and the selector on 2volt, if you connect the cables of a multimeter between the mass of the standard out female bnc and the aluminum frame of the PG506, what a resistance read the multimeter?

thanks eric and thanks to all those who can give any suggestion to understand the problem!
simon


Re: PG506 calibrator generator voltage error

 

I have repaired a number of PG506's and these are the common problems:

Intermittent operation of the flat white relays at the back of the instrument
On older instruments, there are two small metal-cased relays near the front. These switch in a low-pass filter for some standard-amplitude settings to reduce noise from the switching power supply.
Cam switch contacts. To get to these, it is necessary to remove the DVM daughter board
The standard amplitude cal trimpots R340 and R205. I replace the single-turn pots with multi-turn trimmers

To clarify the 50-ohm vs 1 megohm load question, the Standard Amplitude output is intended to drive a 1 megohm load at all ranges. At 10 V and below, it can drive 50 ohms, in which case the output should be exactly half the 1 megohm load value. The High-Amplitude output can drive either a 1 meg or 50-ohm load. The output to a 50-ohm load will be about a tenth of the 1-meg value.

The fast-rise outputs must drive a 50-ohm load.


Bob Haas

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