Date   

Re: 475A trace flicker

Al Testani <atestani@...>
 

Are you sure it isn't the Intensity control itself? The problem may
not necessarily be a function of the brightness setting but the pot
could be intermittant. Maybe putting a temporary pot or resistor in
to prove if the original pot is good or bad would be an easy test.
If it's bad you might try bubbling some CRC 2-26 solvent on the
shaft of the pot so it goes inside and then work the shaft back and
forth many times.

I had several pots on my 475A that were flaky and this procedure
cleaned them up nicely.


--- In TekScopes@yahoogroups.com, "giorgiobottoni" <bottoni@c...>
wrote:
Hi,
i'm working on a 475A with unstable trace brightness.
Seem to be a bad contact problem (quick and random variations).
Defect seem not depend on vertical channel, brightness control
position,
or others control settings.
So i have checked (refresh) almost all in-socket components and
connectors,
crt socket and pins, and so on with no success.
Also "gently beating" over boards not help me to isolate a critic
zone.
Sometimes, trace brightness become quickly very high, so bright
control
can't lower it enough, sometimes brightness are lower than normal.
Sometimes return trace are visible and with same random flickering
too,
but maybe this is another defect.

Many thanks for attention.
Giorgio


Re: Tektronix_Site

Stan & Patricia Griffiths <w7ni@...>
 

Hi Duane,

First, you said this was 535 you have. What is the serial number of it and
what plugin do you have installed? I assume the scope is really a "535" and
NOT a 535A.

You MUST have a plugin installed for the power supplies to regulate. The
plugin puts an essential load on the supplies. If this is a 535, it
originally came with selenium rectifiers. Most 535's have been modified
using a Tektronix mod kit to change the seleniums out for silicon diodes.
Has this mod been done to your 535? It is not just a simple case of
swapping silicon rectifiers for seleniums since some dropping resistors must
also be added in specific places to make it work.

Next, there are a bunch of "black beauty" capacitors throughout this scope
and they should be changed to more modern ones since black beauties leak
electrically and effectively shunt the power supply voltage setting
precision resistors causing the power supplies to go low.

That should get you started. Let me know if I am on the right track . . .

Stan
w7ni@easystreet.com

----- Original Message -----
From: "Duane Kirschenman" <dlkir@bellsouth.net>
To: "Stan & Patricia Griffiths" <w7ni@easystreet.com>
Sent: Monday, September 22, 2003 7:03 PM
Subject: Re: Tektronix_Site


Stan

Thanks for the response. Sounds like you're the 535 talent for which I've
been searching.

Yes, I've checked the 5651 (V609) pin 7 voltage; it's -85vdc, same as
schematic spec.

General symptoms are:
All dc power stage voltages read low (-150 =~-120, 100=~78, 225=~180,
350=~284, 500=~426).
The same is true with all power stage tubes removed.
With only V627 (12b4) removed all the dc power stage voltages read high
(-150 =~-186, 100=~123, 225=~275, 350=~437, 500=~623).

Have you previously encountered such symptoms?

Thanks.

Duane







----- Original Message -----
From: "Stan & Patricia Griffiths" <w7ni@easystreet.com>
To: "Duane Kirschenman" <dlkir@bellsouth.net>; "Bill Den Beste"
<billd@reprise.com>
Sent: Sunday, September 21, 2003 2:03 PM
Subject: Re: Tektronix_Site


Hi Duane,

Have you checked the 5651 reference tube in the -150 Volt power supply
for
correct output voltage? It is sort of critical. I have spares if you
need
one.

I will be glad to coach you to a repair for this scope. I am quite
familiar
with it.

Stan
w7ni@easystreet.com

----- Original Message -----
From: "Bill Den Beste" <billd@reprise.com>
To: "Duane Kirschenman" <dlkir@bellsouth.net>
Cc: <w7ni@easystreet.com>
Sent: Thursday, September 18, 2003 9:31 AM
Subject: Re: Tektronix_Site


Duane,

That scope is a little too old for my personal experience. Stan may
know
more about it.

Often an older instrument will have a few components that have drifted
in
value (even happens to carbon composition resistors).

For example, if resistors in the reference side of the voltage
regulator
have
changed value, the adjustments won't cover the original voltage range.

I'd start looking for the problem by checking the voltages at various
points
in the voltage regulator circuit. If necessary I'd lift one end of
various
components in order to check them with some accuracy.

- Bill



At 07:24 PM 9/17/2003 -0500, you wrote:
Hi,
I'm attempting to revitalize an old Tektronix 535A Oscilloscope; a
very
low
priority project. Your website describes the elder (I'm elder also)
experience that may know something about it.

The problem is that the DC voltages in the five power stages run low.
I
have the manual/schematic and have checked all tubes and the larger
capacitors in the power stages; all appear good. The transformer AC
output
also checks good. The scope seems to function OK, just can't attain
calibration voltage.

Do you recall the cause of any such symptoms, please?

DLK





Re: 475A trace flicker

zenith5106 <zenith@...>
 

--- In TekScopes@yahoogroups.com, "giorgiobottoni" <bottoni@c...>
wrote:
Hi,
i'm working on a 475A with unstable trace brightness.
Seem to be a bad contact problem (quick and random variations).
Defect seem not depend on vertical channel, brightness control
position,
or others control settings.
So i have checked (refresh) almost all in-socket components and
connectors,
crt socket and pins, and so on with no success.
Also "gently beating" over boards not help me to isolate a critic
zone.
Sometimes, trace brightness become quickly very high, so bright
control
can't lower it enough, sometimes brightness are lower than normal.
Sometimes return trace are visible and with same random flickering
too,
but maybe this is another defect.

Many thanks for attention.
Giorgio
-------
Sounds like a bad CRT
/Zenith


475A trace flicker

giorgiobottoni
 

Hi,
i'm working on a 475A with unstable trace brightness.
Seem to be a bad contact problem (quick and random variations).
Defect seem not depend on vertical channel, brightness control
position,
or others control settings.
So i have checked (refresh) almost all in-socket components and
connectors,
crt socket and pins, and so on with no success.
Also "gently beating" over boards not help me to isolate a critic
zone.
Sometimes, trace brightness become quickly very high, so bright
control
can't lower it enough, sometimes brightness are lower than normal.
Sometimes return trace are visible and with same random flickering
too,
but maybe this is another defect.

Many thanks for attention.
Giorgio


(No subject)

jvanderwall1941
 


Re: Tek 310: 10Ω dropping resistors for diode bridges

stan mcintosh <mcintosh@...>
 

Thanks! Having the actual schematic is reassuring. However, I noticed that the designers used 10W resistors. In the case of the -150V line, there is already a 10 ohm (I'll stop using the ascii omega) resistor which shows a voltage drop of 0.3V on the schematic. So, under test conditions specified for the schematic, the diode bridge is supplying 0.03 A (0.3V/10 ohms). Since a 40 ohm goes in series with the 10 ohm resistor as part of the silicon mod, this 0.03 A would have to go through the new resistor as well. Under test conditions, the resistor would then have to dissipate:

0.03 * 0.03 * 40 = 0.036 Watts.

I understand that the current immediately after applying power will be much higher since the capacitor is having to charge. This high current flow is only momentary, though. 10 watts for the resistor rating just seems like a gross overkill.

Am I missing something?

One thing I am not missing, or so I think, is that I intend to add bleeder resistors across the new electrolytics. I have not yet been bitten by a charged electrolytic, and I would like to stack the deck against such an event.

Again, thanks!

stan


Re: Power supply 2246A, 2247A ??

Denis Cobley <denis.cobley@...>
 

Replace all the 1 amp diodes with ZM or ZS marked on them - they go leaky
(about 18 of them).
Don't forget - these are high speed diodes - not 1n4004's.
Regards
Denis

----- Original Message -----
From: "woolyboogur" <wd5jfr@oklahoma.net>
To: <TekScopes@yahoogroups.com>
Sent: Tuesday, September 23, 2003 10:50 AM
Subject: [TekScopes] Power supply 2246A, 2247A ??


At a sale I bought a 2246A, 2246AModA, and a 2247A. The latter 2
were DOA and the 2246A has a dead channel 2. I suspected bad power
supplies in the DOAs and after looking inside I could see on A18 the
power supply board that there had been quite a bit of heat dissipated
around Q2209, Q2210, Q2214, R2254, R2255, R2272, & R2273 all 5.1 ohm
resitors. The 2246A didn't have any signs of overheating and the
2247A board had a high pitched noise like something was trying to
oscillate but not working. After close examination of the A18 boards
I couldn't see any significant difference, so I took a chance and
moved the 2246A board to the 2247A and the 2247A came to life. Now
what I need to do is fix the bad boards or find good replacements.
Any tips on what the root cause of the overheating might be and some
crosses on the transistors would be appreciated.
Thanks
Hank wd5jfr





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Power supply 2246A, 2247A ??

woolyboogur <wd5jfr@...>
 

At a sale I bought a 2246A, 2246AModA, and a 2247A. The latter 2
were DOA and the 2246A has a dead channel 2. I suspected bad power
supplies in the DOAs and after looking inside I could see on A18 the
power supply board that there had been quite a bit of heat dissipated
around Q2209, Q2210, Q2214, R2254, R2255, R2272, & R2273 all 5.1 ohm
resitors. The 2246A didn't have any signs of overheating and the
2247A board had a high pitched noise like something was trying to
oscillate but not working. After close examination of the A18 boards
I couldn't see any significant difference, so I took a chance and
moved the 2246A board to the 2247A and the 2247A came to life. Now
what I need to do is fix the bad boards or find good replacements.
Any tips on what the root cause of the overheating might be and some
crosses on the transistors would be appreciated.
Thanks
Hank wd5jfr


Re: Tek 310: 10Ω dropping resistors for diode bridges

stan mcintosh <mcintosh@...>
 

Thank you very much for your offer of documentation for the silicon
rectifier modification, but a reader just pointed me to a scanned version of
the document on the internet. I do appreciate you offering to make copies,
for a fee or otherwise. I know that the time involved in gathering copies,
parts, whatever is often worth considerably more than the item.

Thanks again!

Sincerely,
stan


Re: Tek 465 Bandwidth Problem

John Miles <jmiles@...>
 

How are you determining it?

-- jm

-----Original Message-----
From: firmecivic [mailto:rgutierrez@tmdsolutions.net]
Sent: Monday, September 22, 2003 3:06 PM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Tek 465 Bandwidth Problem


I repair test equipment as a hobby. I have run across a problem
regarding the bandwidth on the Tek 465 and have yet to decipher it.
I currently have 3 465's with the same problem, the bandwidth is
about half what it should be. All else works fine. This is not an
adjustment issue. Anybody have any suggestions???



Tek 465 Bandwidth Problem

firmecivic
 

I repair test equipment as a hobby. I have run across a problem
regarding the bandwidth on the Tek 465 and have yet to decipher it.
I currently have 3 465's with the same problem, the bandwidth is
about half what it should be. All else works fine. This is not an
adjustment issue. Anybody have any suggestions???


Re: 7854 out of focus problem

Stan & Patricia Griffiths <w7ni@...>
 

On the second problem, the spot that moves behind and then ahead of the real
beam spot . . . that sounds exactly like secondary emission from the mesh
inside the CRT and it sounds "normal", unfortunately . . .

I can't really say on the first problem since I have no experience with the
7854.

Stan
w7ni@easystreet.com

----- Original Message -----
From: "ke4ros" <ke4ros@hotmail.com>
To: <TekScopes@yahoogroups.com>
Sent: Monday, September 22, 2003 5:52 AM
Subject: [TekScopes] 7854 out of focus problem


I have a 7854 that I need some help with. I have gone through the
adjustment/test procedures and all voltage readings/waveforms are OK.
I can get good focus on the top part of the screen, but it gets worse
the further down the screen you go. Everything is still readable, but
out of focus. Could this be the CRT? Bad caps baybe? Any hint of what
to look for? The other problem is what I call 'trace reflection' for
lack of another explaination. With a well defined spot on the screen
even at relatively low intensity moving left to right, I can see a
dimmer 'reflection' of the spot. The reflecton appears to the left of
the trace when the trace is on the left side of the screen and gets
closer to the trace as the trace gets closer to the center of
the screen, then the reflection starts moving to the right of the
trace as the trace moves to the right. It acts like a light beam would
when reflected off of a mirror. Any ideas? Bad CRT again?

Any ideas on either of these problems?

Thanks,
derf


About 7D20 display (att: Bob Morein)

Jose V. Gavila <eb5agv@...>
 

Hello!

I have been looking at the 7D20 Service Manual to get some information
about its display section. It is not all in a single board but main circuit
is at the A6 (display) board. Other items are contained in the A4 (preamp)
and A10 (trigger) boards.

But what I would look first is the self test procedure result (no less than
63 tests are performed), which is displayed using MEMORY DISPLAY buttons.
This test is done on each power cycle. If there is a fault, CSW button will
also light after the test procedure is completed. So, check that and let me
know which MEMORY DISPLAY buttons stay lighted when test stops.

Best regards,

JOSE
----------------------------------------------------------------------
73 EB5AGV / EC5AAU - JOSE V. GAVILA
La Canyada - Valencia (SPAIN)

Vintage Radio: http://jvgavila.com
Vintage Test Equipment: http://jvgavila.com/testeq.htm
European Boatanchors List: http://groups.yahoo.com/group/euro_ba_swap


Re: TEK 453 solid state replacements for the 5642 tubes (HV supply) ?

Stan & Patricia Griffiths <w7ni@...>
 

I'm not familiar with the high voltage diodes you mention, but I know that a
solid state conversion there would be a good idea. I think the 453A used
solid state there.

I have some HV diodes that might work there, too, if you need some different
ones. I think mine are only rated at 5 KV, however. I also have a box of
5642's if you decide to just replace the missing ones. Let me know and I
can send you prices.

Stan
w7ni@easystreet.com

----- Original Message -----
From: "bernard_b2000" <bernard_b@moncanoe.com>
To: <TekScopes@yahoogroups.com>
Sent: Sunday, September 21, 2003 7:44 PM
Subject: [TekScopes] TEK 453 solid state replacements for the 5642 tubes (HV
supply) ?


Just got a good bargain for a 453, this unit had both 5642 rectifier
tubes missing, the HV switching supply is working OK.

Can I substitute the 5642 for a string of high voltage diodes
( or a pair of ECG 518 , 10 kv diodes) ?

The display is there with all functions, but very dim.
What would be the measured voltage at the HV Anode Plug ?
Would appreciate some help on this one !

Thanks to all, keep the good work !

Bernard B.





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Re: 454A Problems

Stan & Patricia Griffiths <w7ni@...>
 

The first problem sounds like a noisey Intensity Control to me and the
second one might be a Tunnel Diode that has drifted off tolerance. I assume
to power supplies all work perfectly . . . right?

Stan
w7ni@easystreet.com

----- Original Message -----
From: <roddefig@netscape.net>
To: <tekscopes@yahoogroups.com>
Sent: Sunday, September 21, 2003 9:30 AM
Subject: [TekScopes] 454A Problems


I have a 454A that every time I adjust the intensity knob the CRT will go
out, or start flickering. Also, when I change the v/div it sometimes also
goes out, or flickers. Does this mean I have to replace the CRT or is it
something else?

The auto trigger doesn't work either (I think). The trigger light never
comes on and I usually end up having to adjust the level knob or turning it
to normal trigger. Can this be fixed?

Thanks,

Michael Roddewig
roddefig@netscape.net

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7854 out of focus problem

ke4ros <ke4ros@...>
 

I have a 7854 that I need some help with. I have gone through the
adjustment/test procedures and all voltage readings/waveforms are OK.
I can get good focus on the top part of the screen, but it gets worse
the further down the screen you go. Everything is still readable, but
out of focus. Could this be the CRT? Bad caps baybe? Any hint of what
to look for? The other problem is what I call 'trace reflection' for
lack of another explaination. With a well defined spot on the screen
even at relatively low intensity moving left to right, I can see a
dimmer 'reflection' of the spot. The reflecton appears to the left of
the trace when the trace is on the left side of the screen and gets
closer to the trace as the trace gets closer to the center of
the screen, then the reflection starts moving to the right of the
trace as the trace moves to the right. It acts like a light beam would
when reflected off of a mirror. Any ideas? Bad CRT again?

Any ideas on either of these problems?

Thanks,
derf


Re: 454A Problems

Rex W. Athey <mister_twister@...>
 

Sounds like a bad/dirty intensity pot. My main 454A had the same problem to some degree. I ended up scrubbing the pot (dis-assembling the pot and cleaning all the pieces & then re-assembling the pot - something I've done a few times, when I'm desperate and can't find a replacement pot). Works fine now. The intensity pot in the 454A does not directly adjust the CRT bias as in some older scopes. They use a form of intensity modulation with this scope - very neat and different, but it works (and it makes it easier to intensity modulate (with the Z axis board)). Hope you can get it working OK. The 454A is one of my all time favorite Tek scopes.

Rex W. Athey


Re: Tek 310: 10Ω dropping resistors for diode bridges

Carl E. Davidson <carlhpretired@...>
 

At the following URL you'll find a PDF document which fully
describes the Tektronix modification kit for replacing selenium
rectifiers with silicon diodes in the 310 oscilloscope:

http://www.messmuseum.de/pdf/tek310mod.pdf

I was mistaken in my earlier suggestion that all you needed were
10 ohm 1 watt resistors. Because of the considerably larger
forward voltage drop across selenium rectifiers vs silicon diodes,
it is necessary, as Stan Griffiths pointed out in message #5087, to
place appropriate high wattage resistors in series with the silicon
diodes to ensure that the correct rectified voltage levels are delivered
to the regulator circuits.

Carl E. Davidson

--- In TekScopes@yahoogroups.com, "stan mcintosh" <mcintosh@t...> wrote:
Several people have emphasized that I need to be sure to include
10Ω dropping resistors for the silicon diode bridges that are
replacing the selenium bridges.

Question: what wattage? Seems like 10W will be good for the -150
line, but I don't have more than one 10Ω/10W resistor in le boxe du
junque. Is 10W overkill for the other two bridges? If not, I can go
by and see if Radio Shack still carries them.

stan

[Non-text portions of this message have been removed]


TEK 453 solid state replacements for the 5642 tubes (HV supply) ?

bernard_b2000 <bernard_b@...>
 

Just got a good bargain for a 453, this unit had both 5642 rectifier
tubes missing, the HV switching supply is working OK.

Can I substitute the 5642 for a string of high voltage diodes
( or a pair of ECG 518 , 10 kv diodes) ?

The display is there with all functions, but very dim.
What would be the measured voltage at the HV Anode Plug ?
Would appreciate some help on this one !

Thanks to all, keep the good work !

Bernard B.


Round Scope Hood

Steve <stever1k@...>
 

I have a Round Scope Hood 016-053 for a Tek Scope if anyone is interested, also parting out a 546 for those needing anything from it.

Steve

176361 - 176380 of 181410