Date   
Re: 1502 TDR project

Tom Gardner
 

I've had a "battery eliminator" that worked in one 1502 but not
another. That's one reason I don't like them. Another is that tabbed C
NiCd cells are easily available, so the battery can be reconstructed.
Battery operation is pleasing; I used one of my 1502s last Saturday in
the middle of a field, to diagnose the cable between a glider's
cockpit and antenna.

You may well be right about the source of a (possibly the) problem,
but using a bench PSU is quick, easy, and eliminates one significant
variable.

On 10/12/2019, Mark Pilant <mark@...> wrote:
Hi Tom.

> I just increased the size of the capacitor in the emulator and she runs
> first time, every time now.

I have a 2200uF cap, per the TekWiki. Works fine for the 1503, so I expect
there is something else going on in the 1502.

> As he said, gotta pay close attention to the "subtleties" of this one!
:-)

That's why I'm still scratching my head. I really need to find some (of
that
rare substance) time to probe with my scope. That way I see what is
happening.
(At least I hope :-)

Re: "liquid crystal driver" sighting

keantoken
 

Liquid crystals are used in welding masks to darken the weld flash instantly. I think they have other applications in high speed photography, and electronic shutters. So maybe this was part of some kind of optics laboratory?

In the original Ebay picture it was possible to read the text on the plugin. On the wiki page the test is unreadable. Here is the full size image with readable text.

https://www.ebay.com/itm/LOT-OF-3-TEKTRONIX-PLUG-IN-5A18N-DUAL-TRACE-AMP-5A15N-AMP-LIQUID-CRYSTAL-DRIVER-/312803078179?nma=true&si=0Rv3bZb%252FLMGiec3%252F7Qc8K%252F3QYFs%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557

Re: 1502 TDR project

Mark Pilant
 

Hi Tom.

I just increased the size of the capacitor in the emulator and she runs
first time, every time now.
I have a 2200uF cap, per the TekWiki. Works fine for the 1503, so I expect
there is something else going on in the 1502.

As he said, gotta pay close attention to the "subtleties" of this one! :-)
That's why I'm still scratching my head. I really need to find some (of that
rare substance) time to probe with my scope. That way I see what is happening.
(At least I hope :-)

- Mark N1VQW

Re: 577 AC collector supply not reading zero on display

DW
 

All done

I used some sand paper and pressed on the variac windings I carefully slid the carbon brush across it to make sure there is even and complete contact patch on the windings.

The stop is adjusted so the brush is setting similar as before, safely on the windings.

I now get at 6.5V and at 50mV a division a 2 division line.

My work is officially done with the variac and everything still works, everything together, covers back on

I should add when i had the wiper parked so far back previously to minimize the collector supply issue, parked off the winding on the plate, I noticed the transition being non linear. Slightly turning the control the voltage would suddenly instantly increase instead of being smooth

Re: 1502 TDR project

fiftythreebuick
 

Mark, as Tom said, it can be a transient condition that trips the power supply.

When developing a battery emulator for my units, at one point mine would fail when the unit was first powered up after sitting idle for a long time, but if you just turned the power off and right back on, it would work every time. The inrush current to all the capacitors in the 1502 was causing a transient low-voltage condition that would trip the power supply. I just increased the size of the capacitor in the emulator and she runs first time, every time now.

As he said, gotta pay close attention to the "subtleties" of this one! :-)

Tom

On Mon, Dec 9, 2019 at 08:53 AM, Tom Gardner wrote:


On 09/12/19 16:38, Mark Pilant wrote:
Hi Tom.

I haven't tried supplying power directly to the banana plugs, but the
parallel cap/resistor battery substitute (ala TekWiki) seems to work
fine, as the battery meter on the front panel indicates the battery is
"good" and I do see 14.4VDC supplying the DC converter.
That's insufficient.

You realise that PSU trips if there is a transient overvoltage. At that point
the voltmeter reads "excessively good" :)

I presume you have read the circuit operation section of the manual?


So it would seem the battery portion of the power supply is working and
I need to determine why the rest of the power supply isn't working.

My general sense is the DC converter is an oscillator driving the T6535
primary to then generate all the secondary voltages needed.  I suspect
the oscillator isn't oscillating (well?), but I'm not sure of the best
way to investigate.  (Not sure how many ways there are to shut it down;
lack of a battery is one.)
One way is the overvoltage detection, via q6547/8/9.


I'm a little wary just probing around with my scope (7904 with the usual
vertical / horizontal plugins), because of potential ground issues.
Although I do have a Tek 224 I can use that shouldn't have any ground
issues.
If you power off a bench supply, then clipping the scope shield to the chassis

is fine.

The 1502's transformer is fully isolated, so**clipping the scope shield to the

chassis is fine.


I just checked, and the power supply for the 1503 is the same as the one
for the 1502.  I may be able to open up my 1503 and use its power supply
to troubleshoot the 1502 power supply.
Yes.

Re: 1502 TDR project

Mark Pilant
 

Hi Dave.

I checked the three caps, and C6415 is open. The other two read good
on my cap/ESR meter (about 400uF and ESR both < .5ohm). I'll definitely
replace the open one, and may do the other two as well.

Looking at the schematic, it looks as though I may be able to test the
board outside the TDR, with a couple of appropriate connections. This
would certainly make things easier.

- Mark N1VQW

Re: 465B soft start?

Abc Xyz
 

Worked on many 465B Scopes?

On Tue, Dec 10, 2019, 10:14 AM <radioconnection@...> wrote:

I have had a few of the 5-volt power0supply bridge rectifiers fail in 465
scopes.



Re: 465B soft start?

Mlynch001
 

I have heard that sitting idle is the worst thing one can do to a scope, such as the 465. I exercise all of my scopes regularly, by turning them on and feeding a signal through the inputs. I have no idea if this helps or not. But I had heard the same advice years ago and thought it made sense to run the scopes from time to time.

--
Michael Lynch
Dardanelle, AR

Re: 577 AC collector supply not reading zero on display

DW
 

You bring a valid point Chuck, I obviously don't want to do more harm than good.

As of wring this I am defaulting the variac brush to its previous state and adjusting the tab stop so the brush sits on the windings. I am making sure the brush will make a contact with a appropriately wider patch on the windings so as to distribute the power in a way that doesn't cause premature wear.

When I am at 5mV a division that is at the 6.5V setting, not 1600V

At this point I will perform some final touches on this curve tracer, after everything is appropriately set I will put the covers back and and leave it alone. Like you mention I don't want to break anything, leave well enough alone. Thanks for all your helpful advise by the way, I learned some things.

Re: 465B soft start?

radioconnection@...
 

I have had a few of the 5-volt power0supply bridge rectifiers fail in 465 scopes.

Re: 577 AC collector supply not reading zero on display

Chuck Harris
 

The first turn on a variac, and the last turn on a variac are both
very vulnerable to damage... physical and electrical.

When properly adjusted, the brush should fully cover (and connect to)
the first through about the 5th turn, and about the 5th to last through
the last when at full scale.

The brush is highly resistive to avoid shorting out the transformer
when it straddles turns. If you were to sharpen the brush to a point,
so that it covered only a single turn, it would burn right through
that turn when operated anywhere near its full current rating.

A pointed carbon brush, pulling very little current will heat to
incandescence long before the skinny little copper wires used in this
variac get to their rated current.

[I used to engrave tools using a pointy carbon rod and a 2V transformer.]

The variac's design requires that the carbon brush be covering 5 or 6
turns, and resistively combining each turn's contribution, to achieve
its full current rating.

This is also required to give the variac seamlessly smooth changes in
output voltage as the voltage control knob is adjusted.

Historically, the variac was invented as a replacement for huge highly
lossy carbon pile rheostats that were used in stage lighting. It was
a real boon, as a variac could be very small, and not get hot... unlike
the rheostats that were being used.

It allowed the light's brightness to be changed smoothly, without jumps.

The variac wasn't meant to go all the way down to zero, only all the
way down to where the flood light is dark.. a couple of volts here or
there didn't matter.

The Tek curve tracer takes this imperfect lamp dimmer device, and
multiplies its output voltages by the step up/down transformer to create
a collector supply that ranges from 0-6.5V all the way up to 0-1500V.

Tektronix never expected that you would use the 50mv per division scale
on the 1500V range. They expected that if you wanted to measure such
a small range of voltages, you would use the 6.5V range.

The only reason you can even see this flaw in your variac is because
it was too expensive to build interlocks to prevent every possible
undesirable setting. They instead concentrated on some of the unsafe
settings.

Are you sure that what you are asking your 577 to do is reasonable?

I would hate to see you do any more damage to your curve tracer.

-Chuck Harris

DW wrote:

I should note the feedback here has been noted and considered so far here.

I have avoided shaping the brush to a sharp point as I was observing how the other variac had a point but it was blunt on the end so I worked to mimic that, somewhat by slightly giving a flat roll off on on just the two ends.

Vertical lines represent contact area to windings.
---||||----------- <Winding
| |
|_ _ | < Brush

| |
| | <Top view of contact area of brush
| | winding aligns perpendicular to this


These adjustments I am making are only brief and temporary, I am just experimenting to see how I can get the collector supply to 0 volts.

Obviously as noted I want to make absolutely sure the carbon brush is making a wide enough contact patch to prolong the life of the variac for the long term.

Also the brush was running off the winding on to a metalic platform. I observed the control slightly sticks as the brush has to overcome the lip of the first winding, as Chuck noted and as I obviously noticed, I don't want this to occur to avoid premature failure. I will readjust approximately.

Re: "liquid crystal driver" sighting

p mc
 

(seeing this a few weeks later)

Glenn,

Like DaveD says, lots of people here can help with TekWiki. Or you can ask kurt.harlem@... for a TekWiki account if you want to get into that yourself.

Back in October I made a stub page with crops from the pictures from the eBay listing:
http://w140.com/tekwiki/wiki/Liquid_Crystal_Driver

A first question might be what type of mainframe the plugin plugs into. If you haven't already sussed that, a picture of the edge connector cut-outs will help.

Curious to see what you've got...

looking for 360 graticule

Phil Cirocco
 

I am looking for a graticule lens for my Tektronix 360 indicator module. This is the old scope module for the 160 series with the round CRT. The 310 scope used the same part. Tektronix part #331-0027-00. I will gladly pay for it and shipping. Any help would be appreciated.

Thanks

Phil Cirocco

Re: 465B soft start?

david
 

Had same cap blow in my 465 two years ago, they don't last forever. Look up Capacitor Reforming on net, it will explain why aluminum caps go bad. I replaced all the filter caps in power supply section and power supply has been good since then. A Wise Man once told me "Machines are made to be run", "If you don't run them they stop working". The oxide layer that insulates plates in cap breaks down and eventually will short out cap if you don't run equipment.

Re: 577 AC collector supply not reading zero on display

DW
 

I should note the feedback here has been noted and considered so far here.

I have avoided shaping the brush to a sharp point as I was observing how the other variac had a point but it was blunt on the end so I worked to mimic that, somewhat by slightly giving a flat roll off on on just the two ends.

Vertical lines represent contact area to windings.
---||||----------- <Winding
| |
|_ _ | < Brush

| |
| | <Top view of contact area of brush
| | winding aligns perpendicular to this


These adjustments I am making are only brief and temporary, I am just experimenting to see how I can get the collector supply to 0 volts.

Obviously as noted I want to make absolutely sure the carbon brush is making a wide enough contact patch to prolong the life of the variac for the long term.

Also the brush was running off the winding on to a metalic platform. I observed the control slightly sticks as the brush has to overcome the lip of the first winding, as Chuck noted and as I obviously noticed, I don't want this to occur to avoid premature failure. I will readjust approximately.

Re: 577 AC collector supply not reading zero on display

k1ggi
 

Google US patent 2,009,013.
It was a case study in a course in an engineering curriculum, taught by R.H.
Rines, son of the patent attorney.
Yes, Rines of Nessie fame.
Ed, k1ggi

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Roy
Morgan
Sent: Tuesday, December 10, 2019 3:00 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577 AC collector supply not reading zero on display

I have seen Variac brushes that were not point shaped at the contact but
rather had s linear shape. The contact end was as long as the brush diameter
but narrowed along the sides so as to contact the full length of the
flattened portion of one or two windings.

Without examining any of the ones here, I suspect they do contact more than
one winding if positioned between two wires in order to create smooth
transition from one winding to the next.

I do have one very old GR Variac whose brush is simply round, and is flat on
the contact end. It may date from the 40's or even 30's.

Roy sends.

On Dec 9, 2019, at 10:57 PM, DW <wilson2115@...> wrote:

What you describe makes sense Chuck. I observe no issues with smoke, hum,
and the variac works throughout its full operating range other than not
going to zero. Therefore I been convinced the variac as far as the winding
is fine.

Having ruled out the variac, Bob made a good point about the carbon brush,
I believe he is on to something about the contact point being worn down
widening the contact area and potentially causing what I am experiencing. I
will try to rework the brush to a point with some sand paper and see if I
notice any improvements.

I would like to thank everyone here for their valuable help, I see this
being useful for someone with collector supply issues to check the wiper
brush!


Pins for 172 Programmable Test Fixture

bobkrassa
 

I am looking for some pins for the 172 Programmable Test Fixture. If anyone has some that they would be willing to sell, please contact me off-list bob@...

Thanks!

73 Bob Krassa AC0JL

Re: 577 AC collector supply not reading zero on display

Chuck Harris
 

In your zeal to get perfection, be sure that you don't let the
brush fall off of the winding when in the most CCW position.

It would not go well for the winding, in the long run.

And note that you will never be able to get exactly zero. This
is because there will always be a fraction of a turn even if
the brush only touches the very last winding.

-Chuck Harris

DW wrote:

As suggested and as I discovered with delight the stop tab is adjustable and moved it further down, that made a big difference, more so then bending it, now I am at about 1.6 divisions at 5mV a division I will attempt to get it to 0 now



Re: 577 AC collector supply not reading zero on display

DW
 

As suggested and as I discovered with delight the stop tab is adjustable and moved it further down, that made a big difference, more so then bending it, now I am at about 1.6 divisions at 5mV a division I will attempt to get it to 0 now

Re: 577 AC collector supply not reading zero on display

Chuck Harris
 

The variac would spit, and spark under load, and the sparking
will cut the sparking wire in half, ruining the variac.

The brush *MUST* contact more than one wire always. That is
crucial to the performance of the variac.

The left hand and right hand stop is fully adjustable to fix
the very problem the OP is complaining of.

-Chuck Harris

Roy Morgan wrote:

I have seen Variac brushes that were not point shaped at the contact but rather had s linear shape. The contact end was as long as the brush diameter but narrowed along the sides so as to contact the full length of the flattened portion of one or two windings.

Without examining any of the ones here, I suspect they do contact more than one winding if positioned between two wires in order to create smooth transition from one winding to the next.

I do have one very old GR Variac whose brush is simply round, and is flat on the contact end. It may date from the 40’s or even 30’s.

Roy sends.

On Dec 9, 2019, at 10:57 PM, DW <wilson2115@...> wrote:

What you describe makes sense Chuck. I observe no issues with smoke, hum, and the variac works throughout its full operating range other than not going to zero. Therefore I been convinced the variac as far as the winding is fine.

Having ruled out the variac, Bob made a good point about the carbon brush, I believe he is on to something about the contact point being worn down widening the contact area and potentially causing what I am experiencing. I will try to rework the brush to a point with some sand paper and see if I notice any improvements.

I would like to thank everyone here for their valuable help, I see this being useful for someone with collector supply issues to check the wiper brush!