Date   

Re: 475B intermittent horizontal

Michael W. Lynch
 

On Mon, Mar 15, 2021 at 06:14 PM, Ondrej Pavelka wrote:


I have cleaned all the switches and viola, all nice and dandy!!
Thank you guys!
Great News! Glad it was a simple fix. Those are the best.

--
Michael Lynch
Dardanelle, AR


Re: 475B intermittent horizontal

Ondrej Pavelka
 

I have cleaned all the switches and viola, all nice and dandy!!
Thank you guys!

The only problem remains the faulty 100x divider module in the attenuator of the 2nd channel. I bought new one some time ago, but it fell apart as soon as i touched it despite being new, it wasn't cheap including postage so i wonder if i should just try again, it originally put me off ordering again.


Re: CRT anode discharge

Matt
 

Bruce,

I had a similar experience in the mid 70's as a young design engineer. I had a multi-input ADC which was implemented with a single ADC, a S/H and a couple of multiplexers. The problem I had with dielectric absorption was with the single sample and hold capacitor where I had initially used a polycarbonate. The side effect of the dielectric absorption was that it caused a small cross-coupling from one channel to the next one that was to be converted due to charge being left on the hold capacitor. Ultimately the problem was resolved by utilizing a Teflon dielectric capacitor which had a very low dielectric absorption, and a price tag reflecting that.

Matt

Hi Bruce,
During a project as a young engineer in the early 70's I was tasked with the design
implementation of a unique multi channel ADC which required input sample-and-hold
blocks. Initially, for the storage caps I naively chose 330 pF ceramic caps that had, in
that application, a bad soak issue.(read: plainly obvious, like 1 to 3ish percent, when
you look on a scope, understand what you're seeing and how to fix it).
It took a bit of head scratching to figure out what was going on... not totally unlike
someone getting zapped by soak, its an effect I'll never forget..

As I recall, both Bob Pease and Al Williams have written of their soak experiences
and knowledge.

Dielectric soak isn't just for folks trying to pinch off that last .001% of THD. ;-)

Roger Marin, KJ7SGV


Re: 454 fireworks

John
 

Sean: If Q1197 isn't s/c it's 99% likely the drive circuitry, which at least is accessible!
John


I built a TM500 mainframe tester, and updated the design. Someone might find this useful?

 

Fellow TM-500 Test Module Constructors,

I've just completed assembling my TM500 test module and after plugging it into a TM501 frame for testing, found that although the 5V indicator illuminated, the -15V and +15V indicators did not.

Probing around a bit I found a puzzling situation. The +15V base drive is routed to the TM501 frame PNP transistor: the one the left side as viewed through the opening from the front. This is labeled Q-12 on the circuit board, near where the leads connect. The transistor on the right side is an NPN and is labeled as Q10 on the circuit board where the leads connect.

The TM501A manual found on TEKWIKI clearly shows Q10 (PNP) on the left and Q12 (NPN) on the right.

I am now wondering if this is traceable to a Tektronix documentation error or whatever.

Has others assembling these modules run into this enigma? I have a TM-502 and a TM504, but thought I would ask first before making any changes or checking into the larger TM-units.

Bruce, KG6OJI


Re: CRT anode discharge

Roger M
 

Hi Bruce,
During a project as a young engineer in the early 70's I was tasked with the design
implementation of a unique multi channel ADC which required input sample-and-hold
blocks. Initially, for the storage caps I naively chose 330 pF ceramic caps that had, in
that application, a bad soak issue.(read: plainly obvious, like 1 to 3ish percent, when
you look on a scope, understand what you're seeing and how to fix it).
It took a bit of head scratching to figure out what was going on... not totally unlike
someone getting zapped by soak, its an effect I'll never forget..

As I recall, both Bob Pease and Al Williams have written of their soak experiences
and knowledge.

Dielectric soak isn't just for folks trying to pinch off that last .001% of THD. ;-)

Roger Marin, KJ7SGV


485 super weak brightness control

Ondrej Pavelka
 

Hi folks,

I acquired some time ago 485 and finally today I managed to spend some time with it.

Cleaning of the switches and moving all the controls back and forth several times brought back most things so I could see both channels working.

Most challenging was/is the

TIME base,
wouldn't scale correctly but after really many turns it now basically does what it should with exception of the last 3 fastest settings. There the picture is all to the side and slowly drifts in but it's very distorted and quite clearly there's something wrong.

I can also see ghost signals like if there was massive jitter or even better described some bounced signals as if the transmission wasnt terminated and I think I can see the signal partly during blank phase. Things are better at higher frequencies and worse on lower. When I enable second time base it's only very faint picture only visible with B intensity at max. But when I move the display all the way to the right I can see very bright spots on the left side so maybe the horizontal signal doesn't have proper connection somewhere and only deflection I can see is some crosstalk?

power supply

all the low voltages look OK, but the high voltage 2950V I can only measure some 2000 volts. It is my first time using 1000x probe for multimeter so I have checked on my lab psu and 30V was correctly showing as 30mV. So it's likely the voltage coming from the multiplier is too low unless the voltmeter impedance despite being so high could drop it down?
Brightness settings both total and B have basically no effect what so ever. They do something but very fine adjustment only.

Fan isn't spinning, any replacement ideas?

Channel 2

1x LED doesn't work
The 1M/50Ohm illumination doesn't work
The 10x and 100x works ok
There was a tantalum in the ch2 attenuator 22uF/15V I replaced because it had a head blown off but it didn't really change anything.
I tested around U80 and shorted the pins associated with lightbulb for 1M/50 and reset lightbulb and pin associated with 1x diode and it looks like these are faulty because they don't light up and there is correct 5V on the other side.

Overall the picture probably could be adjusted to be rather nice and sharp if the brightness could be turned down and the ghost images resolved.
Appreciate if those who been through 485 before could give me some heads up what to look at first and where to look to solve the issues.

P. S. It's got 7 small knobs missing, anybody happen to have some spare parts donor?


Re: Broke my TDS3000B

John Gord
 

David,
Take a look at the EEVBLOG two-part video at:
https://www.youtube.com/watch?v=leC-zSMbtfg
Dave tries to fix a TDS3054 with a single bad channel that has
problems at the same sample rate breakpoint you are seeing.
(He never solves the problem, but his work and the comments
may lead you to a better understanding of which chips do what.)
--John Gord

On Mon, Mar 15, 2021 at 02:47 AM, David C. Partridge wrote:


That makes sense - but which one is it and how to check the enable signal is
being sent to it?

D.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of John Gord via
groups.io
Sent: 14 March 2021 22:45
To: TekScopes@groups.io
Subject: Re: [TekScopes] Broke my TDS3000B

David,
The TDS3000 series scopes have a fast-in, slow-out chip that is used for the
higher sample rates. Apparently that chip is enabled for sample rates above
2.5 million samp/sec, but a normal ADC is used at 2.5M samp/sec and slower.
--John Gord

On Sun, Mar 14, 2021 at 04:54 AM, David C. Partridge wrote:


I've just put it back together after yet another cleaning session, but with
no
change ☹

However I do have something to report which may be useful: If I bring up
the
acquire menu, and select "Fast Trigger" (500 points), then the calibrator
wave
form is display correctly down to a sweep speed of 20us/div (400us/div in
"Normal Resolution" mode). If I go down 10us/div it all breaks up into a
mush
again.

I'm sure this means something useful to someone who knows more about how
this
beastie works.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Martin
Sent: 12 March 2021 13:52
To: TekScopes@groups.io
Subject: Re: [TekScopes] Broke my TDS3000B

I've no idea what I should be looking for and those pins are mighty small
and close together.
Oh yes, thats not easy.

I was thinking about checking if the lines are totally stuck or are looking
normal, i.e. change state every now and then.
Or if a line is moving a little when you switch below 400us... things like
that, to confirm or not if the ASIC really has a problem.

cheers
Martin






Re: Modifying W Plugin to use 6DJ8 Tubes

Dave Wise
 

Addendum. Pictures are in album "Type W Plugin 8416-to-6DJ8 Conversion".


Re: PS 5010 troubleshooting (no negative, erratical display)

 

Second update: after further RTFM it seems that blanking of the display occurs when "the supply is neither in the constant current or constant voltage mode. This happens when the output is foldback current limited or driven into overload by an external source.

Interesting. I have these blinking displays although there is only a DMM connected to them. The DMM displays the correct voltage (with less than 1% deviation). So no overcurrent and no external source...

TBC - cheers
Martin


Re: PS 5010 troubleshooting (no negative, erratical display)

 

First update: I discoverd the switch that allows to select between front and rear panel... it has contact problems.
I toggled it many times until the negative supply came up. Now it seems to work as it should, too.

Remains the erratic display...

cheers
Martin


Re: 308 Data Analyzer

stevenhorii
 

Oz-in-DFW,

I am interested. If you have not already sold them, contact me off-list:
sonodocsch@gmail.com

Thanks

Steve Horii

On Mon, Mar 15, 2021 at 12:48 PM Oz-in-DFW <lists@ozindfw.net> wrote:

If someone wants one, I have a 308 and a 318 that need new homes. One has
probes, but I can remember which at the moment. I'd part with the pair for
$100 plus whatever actual shipping cost is.

--
Oz (in DFW) N1OZ






PS 5010 troubleshooting (no negative, erratical display)

 

Hi all,

I just started to troubleshoot my PS5010. Symptoms are a missing negative output and an erratic display when I switch on the outputs with the on/off key. The supply starts up fine, 5V and plus supply is working as it should. Negative supply can be dialed in as I wish, the relay is clicking when I increase current limit. But it does not give any output at all.

When I switch on the supplies with the on/off key, more often than not and when it is not selected, all the numbers and LEDs of the positive supply go off, then go back on a little later and randomly alternate with the display of the negative supply. When the supplies are in off-mode the display returns to normal.

If anybody has an idea of what that could mean I would be glad to hear about!

cheers
Martin


Re: CRT anode discharge

Alain Mionnet
 

Greenboxmaven

I vorget you...
Does your RCA color 21 inches this?
https://www.youtube.com/watch?v=Wf3M0LYeJdc
12 years ago, was still with analog tv broadcast...
Enjoy with...

It was also Color TV demo at the universal Bruxelles exhibition 17 april 1958 to 19 october 1958
I remember have seen color TV in the USA pavilion (see under a view at 5'30)
https://www.youtube.com/watch?v=JNj3rWPyqug
See the size of the television camera.

It is far and I was just 5 years old mid april....(it was also a very interresting things, Chocolate Cote d'Or who was distributed chocolates for childrens by the trunk of a false elephant !
After all the installations for TV have been keept in place by the RTB (Belgium Television) for many years.
Also as the french 1889 Paris universal exhition where the Eiffel tower have been kept, the Atomium have been kept (with a serious restoration made in 2006( because a lot of corrosion ! and 2008 was fiftieth anniversary))

Alain

France


Re: Repairing broken pots

rick
 

in my Tek products, admitedly from the 1970s and 1980s, the modular pots in them are made by Allen Bradley.

I believe that Bourns had their own, competitive, line of modular pots. Yes, they were Bourns Blue.

Many years later, Allen Bradley sold the Mod-Pot product line to Clarostat, IIRC.

--rick


Re: 2465 time base knob issue

 

The skirt on the 2465 isn't like the skirts on earlier instruments: it's sort of separate from the rest of the knob and appears to maintain it's own spacing from the front panel. I've used exactly that technique when working with the VOLTS/DIV and SEC/DIV knobs on 400-series scopes, however, because it's devilishly easy to get them too close to the front panel and rub off the printing on the back side of the skirt.


Re: 308 Data Analyzer

Oz-in-DFW
 

If someone wants one, I have a 308 and a 318 that need new homes. One has probes, but I can remember which at the moment. I'd part with the pair for $100 plus whatever actual shipping cost is.

--
Oz (in DFW) N1OZ


Re: 2465 time base knob issue

DaveH52
 

Whenever I have to fiddle with those skirted knobs, I slide a piece of cardboard or two between the skirt and the front panel, to provide uniform spacing, then remove it when I'm done.


Re: CRT anode discharge

stevenhorii
 

We once had a sizeable portion of our local power grid go down because a
squirrel had managed to short the terminals of a step-down transformer in
the substation. That tripped the breaker. The power company also explained
this problem for the outage. There was reportedly not much of the squirrel
left. I would have thought the terminals a bit too far apart, but I guess
not.

On Mon, Mar 15, 2021 at 11:27 Alain Mionnet <alain.mionnet@orange.fr> wrote:

For animals who creates a trouble on an electronic board see here (sorry
not in english but pictures);
http://alain.mionnet.pagesperso-orange.fr/daikin.htm
Where a VRV Daikin (external air conditioning unit) was shutdown...
I think I have worked on directly because too many cables and not all with
connectors)
Nota: first and last pictures are the same ! (may an error)

One year ago I have seen a laser metal cutting machine with a trouble in
the PSU.
20 to 25 years old.... 15KV 1 to 2 A ? I have tryed to see about this
product and considered too dangerous to work on.
Finaly the enterprise have buyed a more recent system, sure expensive
but....

Recently I have exchanged a CRT on a TEK 2710.
With the HV connector we must be carefull when un-plug because the male
pin (CRT side) may be easily in contact with unwanted area.(I have
un-plugged in order to check if well voltage on ( I have also a tek 6015 HV
probe, could be used to discharge the HV internal capacitor)

Alain
France






Re: CRT anode discharge

greenboxmaven
 

This is a source of great discussion among audio equipment builders, and off the wall AudioPhools.  An example of deliberately using it for benefit is electret condenser microphones.   I could easily see it coming into play in instrumentation design,  and choosing replacement condensers for restorations.

     Bruce Gentry, KA2IVY

On 3/15/21 1:41, Roger M wrote:
Hi Gordon,
Didn't anyone you worked with, at some point, use the synonymous terms
"dielectric soak" or "dielectric absorption"? If not they sure should have.
Both are pertinent here and oh, so, Google-able. ;-)
-Roger



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