Date   

Re: FS: NOS polystyrene capacitors (was: Help restoring a 547 scope)

Jack Reynolds
 

Thank you for the generous offer. How do we contact you offline?
Thanks,
Jack


Re: Tek 2235 baseline

Harvey White
 

On Wed, 17 Jan 2018 18:22:35 -0800, you wrote:

Hello group.

Problem with channel 1 baseline.
To be able to see the baseline, vertical position pot and also cal pot on channel one has to be totally CCW.
This puts the baseline midway between centerline and top on the screen.
Turning the position knob CW moves the line upwards, so does the cal pot.
If the cal pot moves the trace, there's a balance control that may be
misadjusted. However, that the vert position pot is so far off,
indicates that the amplifier is unbalanced at one point. You can
short the two halves of the amplifier together momentarily and see if
the trace changes location. If it doesn't, then the problem is after
that short.

Harvey



Signals show up nice and clean, but not possible to utilize the whole screen.

Channel two works just fine.

Can someone please guide me toward problematic areas when it comes to vertical adjustment or faults causing this?

Hugo / LA4WKA



Re: Removing / Cleaning transistors connectons etc

Gary Robert Bosworth
 

I have had good results by using CRC QD Electronic Cleaner that I purchased
from O'Reilly Auto Parts. Pep Boys might also sell it. They don't charge
an arm and a leg like many electronic parts stores. Occasionally, I use
Tarn-X on component legs or metal connectors when I see a thin layer of
white or black oxide powder. Two minutes in the Tarn-X, and the surface is
often glossy clean as when new. Anyway, these techniques work for me.

Gary

On Fri, Jan 19, 2018 at 6:11 PM, tinkera123 <@tinkera123> wrote:

Hi all,

I am new to Tektronix scopes and this Forum. Most of my electronics
experience thus far has been with old tube radios ... but I now own a
couple of 7603 scopes ... one has some instability of the trace.

I have been reading the 547 scope Thread and would like to know the best
way to remove transistors and IC’ s from their sockets, and how to clean
them??

Sounds like an easy job, but I would prefer to avoid newbie mistakes .....

Thanks,
Ian



--
Gary Robert Bosworth
@grbosworth
Tel: 310-317-2247


Re: Help restoring a 547 scope EHT

Morris Odell
 

I think you need to be realistic about this. I've restored quite a few tube scopes with this problem - 547, 549, 556 (2 transformers) etc and tried just about everything to get around the problem. Believe me, the ONLY solution you can rely on is to find a good replacement or get the transformer rewound. If Chuck Harris on this group is still doing them, get one of his very well made rewinds. If not, you will have to find another source or try doing it yourself. All the other tweaks - cooling air streams, baking the transformer, replacing the vacuum tube rectifiers with Si diodes, exorcism, magic spells etc are useless or at best a temporary solution. Eventually the transformer will become completely unusable whatever you do.

Morris


Removing / Cleaning transistors connectons etc

tinkera123
 

Hi all,

I am new to Tektronix scopes and this Forum. Most of my electronics experience thus far has been with old tube radios ... but I now own a couple of 7603 scopes ... one has some instability of the trace.

I have been reading the 547 scope Thread and would like to know the best way to remove transistors and IC’ s from their sockets, and how to clean them??

Sounds like an easy job, but I would prefer to avoid newbie mistakes .....

Thanks,
Ian


Re: Help restoring a 547 scope

tinkera123
 

Hi all,
A question rather than a comment ...
How are you removing the transistors from their sockets?? Multi pin IC’s?? How cleaning the pins and sockets??
Ian


TEK 475 low HV

Warren Brewster
 

I have a TEK 475 with no beam.

- Using 475A schematic I have tested all power supply Low voltages and all are correct.

Tested voltage at TP1318 - measures +21.6V
- Waveform is approx 53Kz ( so oscilator running) - however p-p voltage is very low ( around 2Vp-p).
- Disconected voltage multiplier U1321 ( as this seems to be a common fault) - no change
- Reconnected U1321
- Disconnected DC RESTORER circuit ( lifted connection from T1320 to C1320) and TP1318 now runs at approx 40V p-p ( also high voltage multipler works as HV present on tube) so it looks like fault is on DC restorer circuit.

To test where in DC restorer circuit fault is:

- Reconnected C1320 and lifted 10K resister (R1322) and fault reappeared (low oscillator voltage etc) - so appears fault in C1320, CR1320, CR1321 or C1322.
- Replaced all of these with identical components - however fault still present.

Any sugestions of where to look next? - It looks like possible HV leak into filament part of the T1320 winding loading the transformer secondary thus reducing oscillator output??


TEK 475 low HV

Warren Brewster
 

I have a TEK 475 with no beam.

- Using 475A schematic I have tested all power supply Low voltages and all
are correct.

Tested voltage at TP1318 - measures +21.6V
- Waveform is approx 53Kz ( so oscilator running) - however p-p voltage is
very low ( around 2Vp-p).
- Disconected voltage multiplier U1321 ( as this seems to be a common
fault) - no change
- Reconnected U1321
- Disconnected DC RESTORER circuit ( lifted connection from T1320 to C1320)
and TP1318 now runs at approx 40V p-p ( also high voltage multipler works as
HV present on tube) so it looks like fault is on DC restorer circuit.

To test where in DC restorer circuit fault is:

- Reconnected C1320 and lifted 10K resister (R1322) and fault reappeared
(low oscillator voltage etc) - so appears fault in C1320, CR1320, CR1321 or
C1322.
- Replaced all of these with identical components - however fault still
present.

Any sugestions of where to look next? - It looks like possible HV leak into
filament part of the T1320 winding loading the transformer secondary thus
reducing oscillator output??

Regards,
Warren


Re: Tek 475 HV multiplier replacement

Redguuz
 

How about casting in the splice in a 2 component (epoxy) glue or expoy potting formualtion? I could envisage making a small mold out of light cardboard and casting the liquid epoxy into it.
In the past Electronic Shops used to sell special 2 pack epoxy formulations for potting electronics .


Tek 2235 baseline

 

Hello group.

Problem with channel 1 baseline.
To be able to see the baseline, vertical position pot and also cal pot on channel one has to be totally CCW.
This puts the baseline midway between centerline and top on the screen.
Turning the position knob CW moves the line upwards, so does the cal pot.

Signals show up nice and clean, but not possible to utilize the whole screen.

Channel two works just fine.

Can someone please guide me toward problematic areas when it comes to vertical adjustment or faults causing this?

Hugo / LA4WKA


FS: NOS polystyrene capacitors (was: Help restoring a 547 scope)

Brad Thompson <brad.thompson@...>
 

Hello--

If anyone's interested, I can offer three values of NOS polystyrene capacitors
in the following values and voltages:

680 pF +/- 5% @ 125 V. (marked BIEL?The "B" mark is distorted)

1000 pF +/-5% @ 630 V. (note: encapsulated in blue epoxy resin; manufactured by Mial)

0.01 uF +/- 2.5% (H tolerance) @ 33 V. (marked ASC 10000H)

I'm offering these as an assortment-- ten pieces of each value-- 30 pieces total--
for $5.50 which includes shipment via U.S.P.S. mail to U.S. addresses.

Questions welcomed, PayPal honored.

Thanks, and 73--

Brad AA1IP
****
Possibly Asked Questions:

Q.: Are you nuts?! T**ss.com sells polystyrene caps for $1.00 each... and up.

A.: I don't have polystyrene caps in any other values, and if someone can use
these to resurrect an older piece of test equipment or to build a piece of
amateur-radio gear, my work here is done<g>. Besides, I have more than I'll ever use.

Q: Are you sure these are polystyrene caps?

A: Yes-- they melt easily.


Re: Help restoring a 547 scope

Dave Seiter
 

I remember looking for an alternative mfr for whomever one of my clients was buying polystyrene caps from, about 2001 or so.  I'd never come across them before, and the general consensus at the time was "replace them with something more manageable", because none of the top tier manufacturers made them.  
-Dave

From: Chuck Harris <cfharris@...>
To: TekScopes@groups.io
Sent: Friday, January 19, 2018 9:39 AM
Subject: Re: [TekScopes] Help restoring a 547 scope

When I search Mouser for polystyrene caps, they have only one
manufacturer, Xicon, the parts are not ROHS, and they list
only 22 different parts in total.  Sounds a bit like NOS parts
to me.

When I duckduckgo search on polystyrene caps, the theme that
keeps coming up is they are wonderful for a lot of applications,
won't be made in SMD form, but are very difficulty to source.

The second theme that keeps coming up, is "oh, you mean film
capacitors",  which I do not.

I know what I saw in the trade journal way back when, but clearly
there is still some stock available.

After all, the Chinese find value in welding new leads on recycled
transistors, IC's and capacitors.

-Chuck Harris

Geoffrey Thomas wrote:
LCR components, Tredegar, still manufacture them. In fact, they never stopped.

http://www.lcrcapacitors.co.uk/polystyrene/fsc-polystyrene-2/

Geoff.

On 19/01/2018 17:15, Chuck Harris wrote:
I remember a trade journal announcement, that the last
factory went off line, about 10-20 years ago.  It seemed
foolish to me at the time, as the Q of polystyrene caps
isn't easy to match with other varieties.

I would not be at all surprised to find that someone
restarted production, though I am not sure how they
would currently be used.  Surface mount is out of the
question due to high soldering temperatures, and very
low styrene melting point.

-Chuck Harris


Re: Help restoring a 547 scope

ykochcal
 

I would second replacing the HV recitifer tubes with HV solid state diodes
will keep the power and heat down as much as possible.

John

I suggest no matter what the outcome, replace the HV tubes so that filament
power is no longer needed.

-pete


Re: Help restoring a 547 scope

Pete Lancashire
 

HV Transformer

Search through the archives. There is/was a person on the list who rebuilds
them. He biggest issue was it seems the thickness of the insulation used by
Tek was a bit thinner than normal.

I suggest no matter what the outcome, replace the HV tubes so that filament
power is no longer needed.

-pete

On Fri, Jan 19, 2018 at 1:08 PM, felix_cantor via Groups.Io <
felix_cantor=yahoo.com@groups.io> wrote:

ok, sadly it seems that i need to add to my 547`s issues a bad HV
transformer.

I just turned the scope on after cleaning the transistors with their
sockets and the CRT started slowly dimming out after around 20 minutes.
Strange thing though is that yesterday it stayed good all the time. Before
the wash it also did loose brightness over time.

I believe that fixing this issue is quite involved as far as I`ve read.
Bummer. Any tips?

Goode news is that it greatly improved trace stability with the
transistors cleaned up. Now the trace its pretty much perfect besides some
flickering that I think its related to the HV transformer.

Best.




Re: Help restoring a 547 scope EHT

ykochcal
 

Epoxy, EHT, 647 and 547 are good search terms for this issue on the list and
web.

Is your transformer core brown and a little bit compliant to indentation.


I don't think it's that the epoxy so much has water in it that can be dried
out. But that the epoxy has changed which causes more dissipation in the
transformer which then over heats causing saturation of the core.

There have been some reports that baking for a while will reduce heating and
allow them to work for a while, but that does not seem to be a universal
solution or permanent solution and seems to be dependent on how far gone the
transformer is.

I have not read about anyone trying to keep the core cool by just cooling
with a fan.

The combination is interesting possibility for transformers that are not too
far gone: elevate the transformer temp when not using the scope to keep
"dry" as possible, possibly just a power resistor, small supply and a block
of Styrofoam would do, then remove and while using the scope switch to a
fan blowing on the core to keep it cooler.

High voltage caution and warnings would need to be applied.

Possibly staying out of core saturation enough to get some useful life out
of the transformer and scope

Please report back if you give any form of drying a try.

John

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
felix_cantor via Groups.Io
Sent: Friday, January 19, 2018 4:08 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help restoring a 547 scope


Just so that you know i did not wash the HV compartment, it remained nice
and dry.

I also don´t have the filter installed.... we have some darn hot weather
here right now though! ;)

how is the baking process done?

Best.


Re: Help restoring a 547 scope

Chuck Harris
 

Ah ha! Yep, that is what I read too. My internal
squishyware inferred a lack of polystyrene film stock
would spell the end of polystyrene capacitors.

Thanks Ed!

-Chuck Harris

Ed Breya via Groups.Io wrote:

Regarding polystyrene film caps - the story that I recall reading somewhere, is that PS cap production stopped or declined because the only remaining manufacturer of the film stock ended its production. I think the film had to be very special grade for caps, and there wasn't enough volume anymore to keep running it. Who knows how much of the film and NOS PS caps may be in existence? I believe this all happened years ago, but maybe the cap makers did enough LTBs to keep going for a while. Between that and existing caps floating around, it may be some time before they all run out.

Ed


Re: Help restoring a 547 scope

felix_cantor@...
 

Just so that you know i did not wash the HV compartment, it remained nice and dry.

I also don´t have the filter installed.... we have some darn hot weather here right now though! ;)

how is the baking process done?

Best.


Re: Help restoring a 547 scope

ROLYNN PRECHTL K7DFW
 

the CRT started slowly dimming out after around 20 minutes.

=====================================================================


With the two 547s here I've found removing the air filter eliminates the any significant dimming.

My basement is clean and there is no need for the filter. Lowers the internal temperature and, at least with my two, made the dimming disappear or reduced enough that it is not a big problem. There may be a time where this bandage doesn't work but it currently works fine.

Rolynn
Tek Bvtn & Sunset 1966-1971


Re: Help restoring a 547 scope

Richard Knoppow
 

I think about the only way to dry out a transformer is to bake it. There is a technique, which I've never used, of applying some voltage to one winding and shorting the others. That causes the wire to heat. If done within limits it heats the whole transformer and will dry it out. It might also ruin it.
    At -hp- we did not have problems with open frame transformers but did with hermetically sealed ones. If the sealing is not perfect some moisture can get in when washing and can't work its way out again. Such transformers or chokes should be removed when washing.
    I don't think a fan will do much good. A fan may cool a transformer that runs hot but its important to find out why it runs hot. Some equipment just runs hot, like the transformers in my Drake 4 line stuff. Some run hot because the filter capacitors are leaking excessively (the caps may also be hot), sometimes its the proximity of a hot tube. In a few cases its just bad design.

On 1/19/2018 3:23 PM, felix_cantor via Groups.Io wrote:
On Fri, Jan 19, 2018 at 02:12 pm, donald collie wrote:

Apply a small fan to the transformer?
Will that stop the moisture? ...I was thinking something like putting some silica bags around it to suck the moisture out of it and keeping it dry.
--
Richard Knoppow
dickburk@...
WB6KBL


Re: Help restoring a 547 scope

felix_cantor@...
 

I got the manual "Troubleshooting your oscilloscope" by Tektronix and measured the voltage across the tunnel diodes (both A and B) to see if that was the problem with Time Base B not triggering, and both diodes measured around 220mV.

That means that both are leaky? Because there are no problems with Time Base A triggering.... weird. Any hints?


Appreciate it!

Best.