Date   

Re: SC502 With Display Issues

Stephen
 

I will put in the 3904 then. It’s in the power section, not the amplifiers.

And thank you for the offer Ed.
I may need some parts. Will let you know as I move along with repair.


Re: DC503A S1810 repair/replacement ?

Andy Warner
 

Update:

- Locating a new switch was going to be a fools errand
- Repairing the switch also seemed impractical
- I got lucky because the missing signals were simply grounding control
signals F & G depending on the selected function
- Was able to design a small PCB to fit where U1601 was located, and
synthesize the F & G control signals using open-drain 74HC parts

See: https://groups.io/g/TekScopes/album?id=251456

Posted here as encouragement for others who might find themselves in a
similar situation.
Screwed up the rework board in two areas highlighted as A & B in
https://groups.io/g/TekScopes/photo/251456/6

DC503A is working like a champ now, including period B & width B modes,
which were borked previously.

On Fri, Jul 31, 2020 at 10:48 PM Andy Warner <andyw@pobox.com> wrote:

Bought a DC503A a while back (as-is) and finally got around to debugging
its strange behavior.
Turns out the function switch (S1810) is missing a set of wipers.

See: https://groups.io/g/TekScopes/photo/251456/0

In the photo, you can see the two plastic stumps where the wiper is
supposed to be.
It was nowhere to be found, I guess someone must have disassembled the
switch before me to remove the wreckage.

Any suggestions on repair/replacement strategies ?
Anyone got a dead DC503A they would be willing to sell me all or part of
(if so, please contact me off list at: andyw at pobox dot com)
--
Andy



--
Andy


A possibly sick 7904A

Eric
 

I was working on some 7000 series plugins and I noticed some strange behavior out of my 7904A. during the high frequency calibration I found that the scope was a little dim readable for the calibration of the plugin but not bright. To be fair this was at 500 pS/Div sweep speed. But when I turned the brightness all the way up the beam de-focused. I could bring it back in to focus with the front panel however the readout de-focused at that point. Does any one have an idea on where to start looking. If I have to do a full Cal on the frame that is ok as I have one of the -01 calibrators for it. Just trying to get some plugins fixed for the 7854 that is on the way.


Re: SC502 With Display Issues

Ed (SCSKITS)
 

The 2N3904 should do in a pinch, the 2N3565 is only rated at 25V Vce. Only concern might be frequency response if in the vertical or horizontal amplifier circuits.

I am parting out a number of SC503, SC502, and SC504 scopes, if there are some parts you need from the boards, let me know and I will check if I have them. I have bags of transistors that were socketed so I would need the number from one or it's designator on the schematic so I can cross reference to the TEK number.

ed


Re: Looking for front cover for 465 and/or 485

greenboxmaven
 

I think many people consider the covers as shipping material and don't take care of them later unless the scope is used as a portable. A scope sitting on a bench would be sold off later, the cover was "somewhere around here", and got thrown out later once the scope was long gone. For any military test gear from about fifty years ago, covers were deliberately tossed or taken/sent home if possible. The first-term enlisted (often draftee) techies didn't want to deal with keeping everything in inspection order. Once the equipment started coming out as surplus, or slipped through the supply system cracks, they had the covers and rarely used accessories to make a nice instrument for themselves at home. We restore and treasure the TEK gear we have now, but a good portion of it was used in a daily, down and dirty get-it-done environment. As long as it was working well enough to get the particular job done, little else mattered. With the fast obselescence of a lot of communications and industrial equipment, longevity of test gear was not a great concern, and mangement considered the Carbon Unit cost too high to justify anything more than the minimum time needed to keep it functional. That is very different from a lab, broadcast station, or post-Vietnam war military environment. That's my real experience!

Bruce Gentry, KA2IVY

On 8/17/20 3:50 PM, victor.silva via groups.io wrote:
On Fri, Aug 14, 2020 at 07:28 PM, John Brown wrote:

I know. The whole world is looking for covers. Thought I'd ask anyway.
--
W0MPM John
There's some on ebay.



Re: Looking for front cover for 465 and/or 485

victor.silva
 

On Fri, Aug 14, 2020 at 07:28 PM, John Brown wrote:


I know. The whole world is looking for covers. Thought I'd ask anyway.
--
W0MPM John
There's some on ebay.


Re: TDS3000B Series -- Dallas DS1724W-150 NVRAM

David Kuhn
 

" In TDS3000 Series NVRAM contain ONLY User Settings, RealTime Clock and
Operation Hours."

...and the baseline offset calibration.

Dave

On Sun, Aug 16, 2020 at 3:53 PM Valentin <val72ua@gmail.com> wrote:

In TDS3000 Series NVRAM contain ONLY User Settings, RealTime Clock and
Operation Hours.

Best regards,
Valentin,


16 авг. 2020 г., в 22:49, ebrucehunter via groups.io <Brucekareen=
aol.com@groups.io> написал(а):

My newly-acquired TDS3052B fails to retain the time and date upon
power-off. From what I have learned from the group files, this indicates
the battery in the NLA Dallas NVRAM has expired. My questions are:

1. Are the calibration constants stored in this NVRAM?

2. And if so, are they still safely preserved even thought the time and
date are lost?

Bruce, KG6OJI






Re: Looking for front cover for 465 and/or 485

n4buq
 

I wonder if Tek had made the covers for the 400-series scopes more like the one for the 465M, where there's a somewhat useful storage compartment built-in, whether the covers would have stayed with the scopes better over time.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Dave Daniel" <kc0wjn@gmail.com>
To: TekScopes@groups.io
Sent: Monday, August 17, 2020 12:40:15 PM
Subject: Re: [TekScopes] Looking for front cover for 465 and/or 485

The cover for the 485 is similar to those that fit the 465 and 485 (I know
because I owned a 485 with a cover). That is, plastic, no catches other than
a molded clip on either side that snaps over the ‘scope’s outer rim. It’s
outer dimensions are, of course, different than the 465 and 475 covers.

I have never seen a 485 with a DMM option.

DaveD

On Aug 17, 2020, at 12:54, Colin Herbert via groups.io
<colingherbert=blueyonder.co.uk@groups.io> wrote:

Isn't the 485 a bit like the 453, in that the cover is made of metal and is
held in place by catches on either side? The other 400-series scopes have
a plastic cover that just clicks into place. There are two types of
plastic cover, one which is fairly plain and simple and the other which
has the "penthouse" extension. The "penthouse" extension is used with
scopes that have an attached DMM and with the 468, which has the extra
circuitry on top for the digital memory.

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mike
Harmon
Sent: 16 August 2020 01:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] Looking for front cover for 465 and/or 485

I'd love to have a front cover for my 485 as well if someone is fortunate
enough to find multiples!

Mike Harmon, WB0LDJ
mharmon at att dot net









Re: Looking for front cover for 465 and/or 485

Dave Daniel
 

The cover for the 485 is similar to those that fit the 465 and 485 (I know because I owned a 485 with a cover). That is, plastic, no catches other than a molded clip on either side that snaps over the ‘scope’s outer rim. It’s outer dimensions are, of course, different than the 465 and 475 covers.

I have never seen a 485 with a DMM option.

DaveD

On Aug 17, 2020, at 12:54, Colin Herbert via groups.io <colingherbert=blueyonder.co.uk@groups.io> wrote:

Isn't the 485 a bit like the 453, in that the cover is made of metal and is held in place by catches on either side? The other 400-series scopes have a plastic cover that just clicks into place. There are two types of plastic cover, one which is fairly plain and simple and the other which has the "penthouse" extension. The "penthouse" extension is used with scopes that have an attached DMM and with the 468, which has the extra circuitry on top for the digital memory.

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mike Harmon
Sent: 16 August 2020 01:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] Looking for front cover for 465 and/or 485

I'd love to have a front cover for my 485 as well if someone is fortunate enough to find multiples!

Mike Harmon, WB0LDJ
mharmon at att dot net







Re: Looking for front cover for 465 and/or 485

Colin Herbert
 

Isn't the 485 a bit like the 453, in that the cover is made of metal and is held in place by catches on either side? The other 400-series scopes have a plastic cover that just clicks into place. There are two types of plastic cover, one which is fairly plain and simple and the other which has the "penthouse" extension. The "penthouse" extension is used with scopes that have an attached DMM and with the 468, which has the extra circuitry on top for the digital memory.

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mike Harmon
Sent: 16 August 2020 01:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] Looking for front cover for 465 and/or 485

I'd love to have a front cover for my 485 as well if someone is fortunate enough to find multiples!

Mike Harmon, WB0LDJ
mharmon at att dot net


Re: Looking for a P6139A Schematic

 

On Mon, Aug 17, 2020 at 05:20 AM, Roy Thistle wrote:


There's no part number for the cable...
Later Tek catalogs had a section showing all spare parts for probes still in support.
Like this http://www.hakanh.com/dl/docs/probe_parts.pdf I think was scanned from the 1995 catalog.

and I'm not even sure the probe comes apart..
Unscrew the nut that surrounds the cable about half a turn and pull out the cable from the comp box.
On the other end, once the hook is removed, the body shell and tip could be unscrewed.

/Håkan


Re: Looking for a P6139A Schematic

JOE
 

Thanks for the link. It applies to the P6139 not P6139A. Hopefully, but no guarantee, that the "whisker" problem was fixed in the "A" version. I will, however, fully disconnect the cable from the comp box to see which side the short is on.


Re: SC502 With Display Issues

Stephen
 

Is it safe to replace it with a 2N3904? That’s all I have available at the moment.
The 3565 seems to be unobtainium.


Re: SC502 With Display Issues

Stephen
 

It was very hard to see the, not charred, but very dark solder joint to the diode. These transistors are hard to probe. All the leads are extremely short, almost flush on my unit.


Re: SC502 With Display Issues

Stephen
 

After another round of checking and replacing Q940 and Q960 , and making sure I was putting Q940 the right way (E to B of Q935), I noticed that Q935 has a BC short.
Could that induce what I’m getting? It’s probably not good anyways...


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Roger Evans
 

I don't have a 465 so this is hearsay, but I do have a 475 which has some broad similarities. You channel 1 problems sound like an issue with dirty contacts on the attenuator (V/div) and or the input coupling(AC/GND/DC) switches. The standard way to clean the attenuator switches with their cam operated contacts attached to the PCB is to move the switch to a position where the contact is open, slide into the contact gap a strip of paper soaked in IPA, rotate the switch to close the contact, remove the paper strip, repeat ... Search here for some advice on which types of paper are least likely to damage the gold flashing on the contacts. I believe physical access to all the attenuator contacts on a 465 is also a matter of some difficulty. Since the beam moves vertically for some positions it means the dirty contacts are likely to be close to the 'front' end of the attenuator nearest the BNC input and later segments of the attenuator are working mostly OK.

The channel 2 problems could also be poor contacts which sometimes are not 'ohmic' but beyond that they could be tricky to track down without a second scope to check where the distortion comes in. It is worth checking what happens when you pull the 'Invert' button and also what happens with 'Alt' and 'Add' selected on the vertical mode switch.

At this stage, I wouldn't worry greatly about the X1 and X10 lights, the circuitry shouldn't affect the signal integrity. You can at least check around the sensing and switching transistors with a DMM since it all DC/static operation.

Regards,

Roger


Re: SC502 With Display Issues

Stephen
 

On Mon, Aug 17, 2020 at 03:26 AM, Roger Evans wrote:


Stephen,

You said a couple of emails back the emitter of Q940 is at -0.73V. Now you
say R940 has around -19V on one side and around -20V on the other side.
My bad, I confused R940 with R943.

The emitter of Q940 should be the same as one side or other of R940 unless there
is a track burned out on the PCB.
I don't understand the sentence 'With the unit powered OFF, I have close to 0
at the +20 TP, whether it’s ON or OFF'.
It means that I have 0V at this TP, whether the SC502 is in the ON or OFF state.

The bottom end of R940 (again not allowing for burned out tracks) should be
the same as the +20V test point.
I have nothing at the test point.

Is there any visual evidence of damage to the PCB?
Not that I can see. No burn marks, no charred components, nothing. Everything looks normal.

Although I can’t see the other side of the board without removing it.


Re: SC502 With Display Issues

Stephen
 

On Mon, Aug 17, 2020 at 03:20 AM, Harvey White wrote:

Interleaved.

Are you sure you're measuring the +20 volt side on R940 (NOT R943). 
There's no way you could get a negative voltage on that part without
some severe damage and a short between the -20 and + 20

My bad. I’m getting mixed up with all these numbers and references that look almost the same.
That was measuring R943. One both sides, R940 has -0.740V when measured to ground.

R940 is a current sense resistor.  As more current flows out the +20
supply, the voltage drop across it increases.  Once it reaches the
mythical .6 to .7 volts, Q935 starts to conduct.  It steals base current
from Q940, which starts to turn off the pass transistor.  This limits
the current through the supply.
Ok, I think I understand.

The best way to make a measurement on R940 to see if the supply is
limiting is to measure across R940, it gives you an immediate answer. 
The voltages at R940  to ground ought to be pretty much the supply
voltages.  If Q930 were shorted, then that would ground the base of
Q940, which should certainly shut down the supply.  To turn off the
supply, Q930 is turned on.  With the scope running, Q930 should be
turned off.
With the scope running, Q930 is:
B: 0.016V
C: -32.xxV
E: -0.7V

Not sure about the order of EC


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Chuck Harris
 

Depending on your DVM, the input may have significant
capacitance between the + and - probe. The input circuitry
on most is at least 10M, which will keep the capacitance
discharged until you connect to the power supply.

Because the 55V and 110V supplies are stiff, and pretty
low impedance, there is an inrush of current through the
DMM leads to charge the input capacitance, and this forms
a resonant circuit with the test leads, and will make a
small burst of RF.

The scope's trigger is quite good at high frequencies, and
the scope's front end circuitry is very sensitive, so it
can see the broadcast RF from connecting the probes and
trigger.

It is normal.

-Chuck Harris

Greenpitu@gmail.com wrote:

Just to clarify, this observation happened with no probe connected at all to CH1 / CH2:

* When reading +55 and +110 power rails with DMM, on both CH1 and CH2 the trace flickers momentarily and the trigger light comes on - is this normal?




Re: SC502 With Display Issues

Roger Evans
 

Stephen,

You said a couple of emails back the emitter of Q940 is at -0.73V. Now you say R940 has around -19V on one side and around -20V on the other side. The emitter of Q940 should be the same as one side or other of R940 unless there is a track burned out on the PCB.

I don't understand the sentence 'With the unit powered OFF, I have close to 0 at the +20 TP, whether it’s ON or OFF'.

The bottom end of R940 (again not allowing for burned out tracks) should be the same as the +20V test point.

Is there any visual evidence of damage to the PCB?

Roger

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