Date   

Replacing CC resistors

Michael Dunn <mdunn@...>
 

Yes, old carbon comp resistors *can* drift. Just a thought: if you're replacing CCs with film resistors, keep in mind one of CC's attributes - their high surge capacity. Analyze or measure the circuit (most likely during turn-on), and overrate the replacement's power if necessary.

Michael


Re: Tek475 strangely in heat

adenton <adenton@...>
 

Hot means too much current at too much voltage -- power = volts x
amps and all that. If the voltages are OK look for excessive
current. High heat is NOT normal. A common cause of excess current
is a leaky capacitor, either supplying excessive base current, or for
example in bypassing an emitter resistor thus greatly increasing
emitter/collector current.

Depending on the circuit configuration, it is possible for this to
happen without apparent malfunction, especially in a differential-
amplifier circuit. Since yours are duals, I strongly suspect that.
Check all those caps for leakage. Strap a current meter in one of
the emitter circuits and measure the juice. This times the CE
voltage gives you the power dissipation which you can compare against
the case type. (Although you already know it's too high.)

Note, caps sometimes check OK at low voltages (VOM ohmmeter) but leak
like fishnet at circuit voltages. Perhaps a current-meter in series
with the cap, with the circuit quiescent. (If it's in the sweep, try
single-sweep mode etc.)

Which suggests a topic, Does anyone know anything about electrolytic
capacitor leakage??? (JUST KIDDING!!!)

--- In TekScopes@yahoogroups.com, "josko_flander"

A pair of double transistors (Q914 and Q938) is literarily
steaming. They are too hot to touch.


Scope humour

Michael Dunn <mdunn@...>
 

Came across this joke as a young lad, and though I knew what a 10:1 probe was, it took a friend and I literally several years before we "got it"! If you don't understand, try saying it out loud a few times.

Q: Why are they called 10:1 probes?

A: Because when left unattended, they 10:1 away.


7104 Service Manual wanted

Bruce Lane
 

Hi, gang,

OK... I've checked my usual sources. Cheapest price I've seen so far for a service manual (original Tek hardcopy) for the 7104 was $135.00.

That really seems kind of high. I know there's at least a couple of listmembers who sell manuals -- that being the case, I'd like to hear from you if you can beat that price.

The serial number involved is B021884.

Thanks much.
-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies -- http://www.bluefeathertech.com
kyrrin (at) bluefeathertech do/t c=o=m
"If Salvador Dali had owned a computer, would it have been equipped with surreal ports?"


Re: GR, not Tek!

regman10
 

Thanks Craig,
Very interesting site. It made me appreciate my V5 Variac (in almost daily
use for over 30 years) and decade resistor box even more.

"Subject: [TekScopes] GR, not Tek!"


Tek475 strangely in heat

josko_flander
 

Hi!

I have recently acquired an old Tek475 scope and although it works
great I was tempted to poke my nose in it. There I found something
strange. A pair of double transistors (Q914 and Q938) is literarily
steaming. They are too hot to touch. I have made some preemptive
measurments (compared the voltages in the circuit to those in the
schematics) but it all checks fine. I was wandering if it is their
normal working temperature or they are overheating and are about to
die.

Any comment would be sincerely appreciated!

Thanks!

Josko Flander


5L4N

Stefan Heinzmann <stefan_heinzmann@yahoo.com>
 

Hi all,

there's a lot of 15 5L4N spectrum analyzer plugins on ebay at the
moment (item 3071668755). Never heard of those, are they any good?
1000 Euros for 15 of them means less than 70 for each one. How do they
compare to a 7L5? Bargain?

(Now don't ask me what you do with 15 at a time...)

Cheers
Stefan


7104

spectrabei <spatial_electronics@...>
 

Resistors are vary stable, If your looking to a resistor
as the source of your focus voltage problem your on the wrong
track. Check a 200 volt zener diode (VR1784) on the high voltage
(A22)Board.
Enough of this about resistors. High Voltage problems are usually
the result of a breakdown of the dielectric in the high voltage
caps or a breakdown of the PN junction in a high voltage diodes.
The 200 volt Zener sets the collector switching voltage for
transistor Q1784.


Steve


More New Photos

oldtek2003
 

If anyone's interested, I've added some photos of a recent
restoration/repair job of an older 316 scope (in 316).

Tony Denning


7103

Craig Sawyers <c.sawyers@...>
 

Those interested in a 7103 (rack mounting version of 7104, with only three
slots), there is one listed at the moment on eBay number 2589050283 for $139
Buy It Now.

Craig


Carbon resistors, was 7104: Self-blurring focus

Craig Sawyers <c.sawyers@...>
 

I have found the same thing. I always verify the value of caps and
resistors in my spare parts box before using them.
If you check the archives, there was quite a discussion about this around a
year ago.

Craig


Re: Any way to clean...?

Jeff W <vwthingy@...>
 

Bruce wrote:
Does anyone know of a way to clean the (apparently sealed)
pots on the front panel of a 7000 series?

I have found that the cycling them results in a very temporary fix.
I have become pretty good with taking apart these pots, cleaning
them, and putting them back together. In the past, I used to just
collect the excess grease and recycle it, but I recently picked up a
couple tubes of Electrolube contact oil to try out.

Jeff


Re: 7104: Self-blurring focus

regman10
 

I have found the same thing. I always verify the value of caps and
resistors in my spare parts box before using them.


I've been starting to notice a problem with most carbon resistors in general
that they are way off in value.


Re: 7104: Self-blurring focus

Rex W. Athey <mister_twister@...>
 

I've been starting to notice a problem with most carbon resistors in general that they are way off in value. I discovered this when a couple years ago I went through some of my parts inventory and found values to be way out of tolerance. Best example I remember was 47K, probably because I had some many of them. Now when ever I get replacement resistors, I avoid carbon resistors as much as I can for this reason. Have not had any problems replacing resistors in any piece of equipment since. There are some exceptions, but I now try to avoid the aggrevation of carbons all together. I'm mostly talking old carbon resistors in inventory.

Now I'll probably start a bad resistor thread to go with the bad electrolytics / paper caps threads. Been weeding out some of them too.

Rex


GR, not Tek!

Craig Sawyers <c.sawyers@...>
 

Hi all

Anyone interested in the history of GR, I found a downloadable 1916
catalogue here
http://www.teradyne.com/corp/grhs/pdf/catalog-bulletins/Catalog_A_1916.pdf .
In fact this is just a section in the General Radio Historical Society on
http://www.teradyne.com/corp/grhs/ - it seems to have lots of fascinating
stuff there if you like the early history of electronics.

Enjoy!

Craig


Re: 7104: Self-blurring focus

John Miles <jmiles@...>
 

Usually aged resistors in the focus voltage divider are responsible for this
symptom. They may be potted in a hybrid, in which case you'll have to break
some traces and rebuild the divider on an outboard basis.

I am slowly learning to view all carbon-composition resistors above 100K
ohms with the same suspicion that people reserve for old paper capacitors.

-- john KE5FX

-----Original Message-----
From: Bruce Lane [mailto:kyrrin@bluefeathertech.com]
Sent: Thursday, January 15, 2004 3:47 PM
To: tekscopes@yahoogroups.com
Subject: [TekScopes] 7104: Self-blurring focus


Well... I think I may have a couple of leaky caps or something.

Having cycled the pots a whole bunch on my newly-acquired
7104, I find that they're doing well enough. However, it looks
like there may be an issue in the focus section.

What will happen is that the trace will be razor-sharp and
hair-fine one moment, and then it'll start blurring. This affects
the entire screen (readout included). The interesting thing is
that the focus will blur up to its (apparent) maximum degree of
'defocused,' and then it'll snap back to razor-sharp and clear.
It'll do this three or four times, and then stay sharp or blurred
at any given moment. After the 'scope's been on for an hour or
so, this behavior disappears.

Has anyone seen this symptom before? I suspect
thermal-intermittent caps in the high-voltage area, but I don't
yet have a service manual for the unit. Pointers appreciated.

Thanks much.


-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies -- http://www.bluefeathertech.com
kyrrin (at) bluefeathertech do/t c=o=m
"If Salvador Dali had owned a computer, would it have been
equipped with surreal ports?"




Yahoo! Groups Links

To visit your group on the web, go to:
http://groups.yahoo.com/group/TekScopes/

To unsubscribe from this group, send an email to:
TekScopes-unsubscribe@yahoogroups.com

Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/



7104: Self-blurring focus

Bruce Lane
 

Well... I think I may have a couple of leaky caps or something.

Having cycled the pots a whole bunch on my newly-acquired 7104, I find that they're doing well enough. However, it looks like there may be an issue in the focus section.

What will happen is that the trace will be razor-sharp and hair-fine one moment, and then it'll start blurring. This affects the entire screen (readout included). The interesting thing is that the focus will blur up to its (apparent) maximum degree of 'defocused,' and then it'll snap back to razor-sharp and clear. It'll do this three or four times, and then stay sharp or blurred at any given moment. After the 'scope's been on for an hour or so, this behavior disappears.

Has anyone seen this symptom before? I suspect thermal-intermittent caps in the high-voltage area, but I don't yet have a service manual for the unit. Pointers appreciated.

Thanks much.


-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies -- http://www.bluefeathertech.com
kyrrin (at) bluefeathertech do/t c=o=m
"If Salvador Dali had owned a computer, would it have been equipped with surreal ports?"


Any way to clean...?

Bruce Lane
 

Does anyone know of a way to clean the (apparently sealed) pots on the front panel of a 7000 series?

My 7104 works great, but the intensity and focus pots are noisy as sin. Is it just a case of working them back and forth until they clear up or what?

Thanks much.


-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies -- http://www.bluefeathertech.com
kyrrin (at) bluefeathertech do/t c=o=m
"If Salvador Dali had owned a computer, would it have been equipped with surreal ports?"


3A10 manual/scan

Tim Phillips <t.phillips@...>
 

Hi, all;
many thanks to all the people who kindly sent me info about
the 3A10. My problem with BAMA download was caused by me using
a really ancient version of Acrobat.
kindest regards
Tim.
p.s. I would really like a 3A10 ! c'mon ebay etc. ;-)


7503 repair

lloydepowell <lloydepowell@...>
 

Does anybody have a Tek 7503 mainframe repair manual? Does anyone
know how close it is to a 7603?

181881 - 181900 of 188105