Date   

Re: Tektronix 7104 and 7D20 showstopping?

glennmhdk
 

--- In TekScopes@yahoogroups.com, David <davidwhess@...> wrote:
...

It would not surprise me if Tektronix lowered the readout repetition
rate in the 7104 so it would not cause as much damage. The various
plug-in instruments which generate their own display would not include
this protection.
Hi group

From:
http://www.vintagetek.org/wp-content/uploads/2011/10/7104-Springer-article-email-res.pdf
It can be read on pdf-page 3, that the MCP gain can be varied by changed the MCP bias voltage.

At page 323 the MCP output voltage can be varied by (R1720 MCP gain) and by "INT SENSE P1705 (P1705 hard to read)". R1720 can not be controlled at the front, so it must some sort of trimpot:
http://bama.edebris.com/download/tek/7104/tek-7104.pdf

-

Regarding how the CRT works.

How can it be, that the input MCP potential is only +2265V? (grounded relative to the cathode at -2265V). Even though the anode voltage is some multipla of 2400V, the MCP "intercepts" the high anode potential? This ought to mean, that the electrons are only accelerated by +2265V - and not e.g. by 5*2400V+2265V (do not know if it is exactly 5)?

Only after the MCP, are the electrons fully accelerated. But the electron beam was focused before the MCP? This appearently do not make sense? Do somebody know how this works or can point to some page?

Glenn


Re: Coaxial Attenuator Naivete - Please Help

stan_katz
 

David,

Price is right. I trust your recommendation.

Thanks,
Stan

--- In TekScopes@yahoogroups.com, David <davidwhess@...> wrote:

I have been picking up BNC and SMA coaxial attenuators at Ham swap
meets and on Ebay.

I have one of the 50 Ohm feedthrough terminators shown here which
works fine up to at least 300 MHz. I could test it higher but have
not had a need to. They are OEMed for a bunch of different companies:

http://www.mpja.com/Scope-Probes--Test-Leads/products/57/

On Sun, 07 Apr 2013 04:25:38 -0000, "stan_katz" <stan_katz@...>
wrote:

I've now learned the hard way that coaxial feedthrough attenuators are not trivial. I thought I could purchase cheap from asia without the seller specifying bandwidth. I wound up with a 10X attenuator that is 10X at ONLY 150khz! The 2X attenuator...only at 50khz. It's almost as if they were notch filters. A disaster. I tracked down an inexpensive domestic source that specified DC - 1Ghz for the same attenuator values. I'm not holding my breath that these will be flat as a board, like branded ones (Tek,HP, Probemaster, et.al) that sell for $20.00 and up on Ebay. I'm also having second thoughts on the asia sourced 50ohm terminator resistors I ordered. If they used spiral cut metal films in them, I've got unwanted inductance there. Even if the resistors are non-inductive, I now realize that dropping a 50ohm terminator on a BNC Tee, and proceeding with a calibration per Tek cal. procedure, could be a fools errand. There will be much more LC due to the connectors and distance from scope
input. I need a feedthrough 50hm terminator for serious cal. work. Right? Can anyone point me to a reliable third party vendor of new quality coaxial attenuators that can come in at a price point below $20.00 per connector? In the meantime, I'll be bidding on the name brands, and hoping for the best.

Hope this post helps newcomers avoid my painful lesson.

Stan


Re: Discussion of Tek circuits

Carlos
 

--- In TekScopes@yahoogroups.com, "John S" <John@...> wrote:

I was motivated to purchase a copy of "Wideband Amplifiers" (P Staric & E Margen) by someone on this forum. Deals with T-coils, transforms and filter theory.

John
I know this is an old thread. Just wanted to say that if someone is interested in this book, I found it can be downloaded here:

http://en.bookfi.org/book/715016

Regards,

Carlos


Re: Tektronix 547 Oscilloscope and Plug-Ins for sale.....

R Wall ml <maillistrw@...>
 

Hi Dave,
 
Oppsss... you are correct. I must have remembered using a Tektronix storage scope back in the 1980s when I worked for Control Data Australia. It’s a 547 oscilloscope which is not a storage oscilloscope.
 
Sorry,
 
Roderick Wall.
 

From: David
Sent: Sunday, April 07, 2013 3:41 PM
Subject: Re: [TekScopes] Tektronix 547 Oscilloscope and Plug-Ins for sale.....
 
 

I have a 547 but do not remember any storage functions. Maybe you
actually have a 549?

http://www.barrytech.com/tektronix/vintage/tek547.html
http://www.barrytech.com/tektronix/vintage/tek549.html

On Sun, 7 Apr 2013 15:37:12 +1000, "R Wall ml"
<mailto:maillistrw%40optusnet.com.au> wrote:

>Sorry I should have changed the subject.
>
>Roderick.
>
>From: R Wall ml
>Sent: Sunday, April 07, 2013 2:48 PM
>To: mailto:TekScopes%40yahoogroups.com
>Subject: Re: [TekScopes] Re: Planning 2467B LVPS re-cap
>
>Hi,
>
>I have the following items for sale, are there any reasonable offers before I put them on Ebay.
>
>(1) Tektronix 547 Oscilloscope with a Type 1A4 four channel plug-in Unit. Also has the hood for the screen and a pouch to put probes in. It has some non Tektronix probes.
>(2) Type Z Plug-in Unit. Calibrated Differential Comparator +/-2000 CM Dynamic Scale length. S/No: 004174.
>(3) Type O Operational Amplifier Plug-in Unit. S/No:001583. With Gating Adaptor for Type O Plug-in.
>(4) Type Q Plug-in Unit. Transducer and strain Gage Preamp. Rise time around 60uSec Bandwidth around DC to 6Kc. S/No: 001479.
>(5) Type 1A4 Four Channel Amplifier. S/No: B072831.
>(6) Type 1A7 Plug-in Unit. High Gain Differential Amplifier. S/No: 000119. Looks to have a part missing as there are two bare wirers going nowhere.
>(7) Type 53/54E Plug-in Unit. Low-Level Differential Calibrated AC Preamp 0.05-10Mv/CM. S/No: 1551.
>
>All the above have manuals with circuits. On the odd occasion I have used the 547 oscilloscope. On power up (7/Apr/2013) the oscilloscope triggers and shows the square wave calibration voltage. This is a storage scope with the trace storage being on the screen, not in memory. A sticker on the back states: Calibration Date: 12/11/80. I have not tested the Plug-ins, they look complete except for the 1A7 Plug-in with two disconnected wires. There are no DUT connecting cables.
>
>Note, the above equipment is located in Melbourne Australia. Purchaser to pick up or pay for postage/shipment.
>
>Please reply off this group,
>
>Regards,
>
>Roderick Wall.

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Version: 2013.0.3272 / Virus Database: 3162/6229 - Release Date: 04/06/13


Re: Tektronix 547 Oscilloscope and Plug-Ins for sale.....

 

I have a 547 but do not remember any storage functions. Maybe you
actually have a 549?

http://www.barrytech.com/tektronix/vintage/tek547.html
http://www.barrytech.com/tektronix/vintage/tek549.html

On Sun, 7 Apr 2013 15:37:12 +1000, "R Wall ml"
<maillistrw@optusnet.com.au> wrote:

Sorry I should have changed the subject.

Roderick.

From: R Wall ml
Sent: Sunday, April 07, 2013 2:48 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: Planning 2467B LVPS re-cap

Hi,

I have the following items for sale, are there any reasonable offers before I put them on Ebay.

(1) Tektronix 547 Oscilloscope with a Type 1A4 four channel plug-in Unit. Also has the hood for the screen and a pouch to put probes in. It has some non Tektronix probes.
(2) Type Z Plug-in Unit. Calibrated Differential Comparator +/-2000 CM Dynamic Scale length. S/No: 004174.
(3) Type O Operational Amplifier Plug-in Unit. S/No:001583. With Gating Adaptor for Type O Plug-in.
(4) Type Q Plug-in Unit. Transducer and strain Gage Preamp. Rise time around 60uSec Bandwidth around DC to 6Kc. S/No: 001479.
(5) Type 1A4 Four Channel Amplifier. S/No: B072831.
(6) Type 1A7 Plug-in Unit. High Gain Differential Amplifier. S/No: 000119. Looks to have a part missing as there are two bare wirers going nowhere.
(7) Type 53/54E Plug-in Unit. Low-Level Differential Calibrated AC Preamp 0.05-10Mv/CM. S/No: 1551.

All the above have manuals with circuits. On the odd occasion I have used the 547 oscilloscope. On power up (7/Apr/2013) the oscilloscope triggers and shows the square wave calibration voltage. This is a storage scope with the trace storage being on the screen, not in memory. A sticker on the back states: Calibration Date: 12/11/80. I have not tested the Plug-ins, they look complete except for the 1A7 Plug-in with two disconnected wires. There are no DUT connecting cables.

Note, the above equipment is located in Melbourne Australia. Purchaser to pick up or pay for postage/shipment.

Please reply off this group,

Regards,

Roderick Wall.


Tektronix 547 Oscilloscope and Plug-Ins for sale.....

R Wall ml <maillistrw@...>
 

Sorry I should have changed the subject.
 
Roderick.
 

From: R Wall ml
Sent: Sunday, April 07, 2013 2:48 PM
Subject: Re: [TekScopes] Re: Planning 2467B LVPS re-cap
 
 

Hi,
 
I have the following items for sale, are there any reasonable offers before I put them on Ebay.
 
(1) Tektronix 547 Oscilloscope with a Type 1A4 four channel plug-in Unit. Also has the hood for the screen and a pouch to put probes in. It has some non Tektronix probes.
(2) Type Z Plug-in Unit. Calibrated Differential Comparator +/-2000 CM Dynamic Scale length. S/No: 004174.
(3) Type O Operational Amplifier Plug-in Unit. S/No:001583. With Gating Adaptor for Type O Plug-in.
(4) Type Q Plug-in Unit. Transducer and strain Gage Preamp. Rise time around 60uSec Bandwidth around DC to 6Kc. S/No: 001479.
(5) Type 1A4 Four Channel Amplifier. S/No: B072831.
(6) Type 1A7 Plug-in Unit. High Gain Differential Amplifier. S/No: 000119. Looks to have a part missing as there are two bare wirers going nowhere.
(7) Type 53/54E Plug-in Unit. Low-Level Differential Calibrated AC Preamp 0.05-10Mv/CM. S/No: 1551.
 
All the above have manuals with circuits. On the odd occasion I have used the 547 oscilloscope. On power up (7/Apr/2013) the oscilloscope triggers and shows the square wave calibration voltage. This is a storage scope with the trace storage being on the screen, not in memory. A sticker on the back states: Calibration Date: 12/11/80. I have not tested the Plug-ins, they look complete except for the 1A7 Plug-in with two disconnected wires. There are no DUT connecting cables.
 
Note, the above equipment is located in Melbourne Australia. Purchaser to pick up or pay for postage/shipment.
 
Please reply off this group,
 
Regards,
 
Roderick Wall.

No virus found in this message.
Checked by AVG - www.avg.com
Version: 2013.0.3272 / Virus Database: 3162/6229 - Release Date: 04/06/13

No virus found in this message.
Checked by AVG - www.avg.com
Version: 2013.0.3272 / Virus Database: 3162/6229 - Release Date: 04/06/13


Re: FS Type 184 Time Mark Generator

d.seiter@...
 

Agreed,

I've had four, and never spent more than $35 on one, and I've sold them for $20, $29, and $65.  Most were "average" condition, with stickers, broken rear feet, etc.  My "keeper" was built with parts from the others.  The one I sold for $65 was actually the worst of the lot; it had no rear feet, and adjustment holes drilled through the top and bottom. 

-Dave



From: "David DiGiacomo"
To: TekScopes@...
Sent: Saturday, April 6, 2013 5:42:36 PM
Subject: Re: [TekScopes] FS Type 184 Time Mark Generator

 

> I am thinking about $150 + shipping. I see them on EBay in the $200 range.

You most certainly do not. Look at the actual sold listings, not the
fantasy listings.


Re: Mild OT question – Checking diodes

 

On Sat, 06 Apr 2013 19:38:21 -0000, "Robert"
<go_boating_fast@yahoo.com> wrote:

Had this thought reading Craig Sawyers 7844 repair work:

Recently working on a 485, I used a simple diode curve trace set up. One of the diodes clearly showed bad, probably leaky. Initially that diode would still show some forward reverse difference on a DMM diode test. Does this seem reasonable? I am beginning to doubt the DMM diode test, or if I use the DMM test correctly.

Bob
A DMM diode test is only good for measuring the forward voltage drop
and the reverse leakage at low voltages which is good enough for
diodes that fail short or open. Unfortunately a common failure mode
in high voltage low current circuits involves high reverse leakage and
zener like behavior which a DMM diode test will not detect. For that
you need a curve tracer or even just a high voltage power supply and a
current meter.


Re: Coaxial Attenuator Naivete - Please Help

 

I have been picking up BNC and SMA coaxial attenuators at Ham swap
meets and on Ebay.

I have one of the 50 Ohm feedthrough terminators shown here which
works fine up to at least 300 MHz. I could test it higher but have
not had a need to. They are OEMed for a bunch of different companies:

http://www.mpja.com/Scope-Probes--Test-Leads/products/57/

On Sun, 07 Apr 2013 04:25:38 -0000, "stan_katz" <stan_katz@yahoo.com>
wrote:

I've now learned the hard way that coaxial feedthrough attenuators are not trivial. I thought I could purchase cheap from asia without the seller specifying bandwidth. I wound up with a 10X attenuator that is 10X at ONLY 150khz! The 2X attenuator...only at 50khz. It's almost as if they were notch filters. A disaster. I tracked down an inexpensive domestic source that specified DC - 1Ghz for the same attenuator values. I'm not holding my breath that these will be flat as a board, like branded ones (Tek,HP, Probemaster, et.al) that sell for $20.00 and up on Ebay. I'm also having second thoughts on the asia sourced 50ohm terminator resistors I ordered. If they used spiral cut metal films in them, I've got unwanted inductance there. Even if the resistors are non-inductive, I now realize that dropping a 50ohm terminator on a BNC Tee, and proceeding with a calibration per Tek cal. procedure, could be a fools errand. There will be much more LC due to the connectors and distance from scope
input. I need a feedthrough 50hm terminator for serious cal. work. Right? Can anyone point me to a reliable third party vendor of new quality coaxial attenuators that can come in at a price point below $20.00 per connector? In the meantime, I'll be bidding on the name brands, and hoping for the best.

Hope this post helps newcomers avoid my painful lesson.

Stan


Re: Tektronix 7104 and 7D20 showstopping?

 

The best I have found is the Electronic Design article which is linked
here:

http://www.vintagetek.org/tag/micro-channel-plate-crt/

On Sun, 07 Apr 2013 14:17:59 +1000, Don Black
<donald_black@bigpond.com> wrote:

Is there a concept book that describes the micro-channel tube and how it
works?

Don Black.

On 07-Apr-13 5:23 AM, Craig Sawyers wrote:

Then there is the internal 7104 readout display.

Why does this not burn-out MCP?
It does. That is why the readout intensity knob has an off position, and a
pulsed mode that operates in several ways depending on a range of
settings.
If you leave it operating continuously it will absolutely reduce the
sensitivity of the MCP at the readout positions. I have some images in the
pics section of Tekscopes that show an image of a single shot trace at
200ps/div from a TD pulser. Those were taken with a Tek C1002 CCD camera.
The slight graininess of the trace is due to the granular nature of
individual electrons striking the MCP before amplification. It is a
helluva
tour de force of analogue scope engineering to do this.

Craig


Re: Planning 2467B LVPS re-cap

R Wall ml <maillistrw@...>
 

Hi,
 
I have the following items for sale, are there any reasonable offers before I put them on Ebay.
 
(1) Tektronix 547 Oscilloscope with a Type 1A4 four channel plug-in Unit. Also has the hood for the screen and a pouch to put probes in. It has some non Tektronix probes.
(2) Type Z Plug-in Unit. Calibrated Differential Comparator +/-2000 CM Dynamic Scale length. S/No: 004174.
(3) Type O Operational Amplifier Plug-in Unit. S/No:001583. With Gating Adaptor for Type O Plug-in.
(4) Type Q Plug-in Unit. Transducer and strain Gage Preamp. Rise time around 60uSec Bandwidth around DC to 6Kc. S/No: 001479.
(5) Type 1A4 Four Channel Amplifier. S/No: B072831.
(6) Type 1A7 Plug-in Unit. High Gain Differential Amplifier. S/No: 000119. Looks to have a part missing as there are two bare wirers going nowhere.
(7) Type 53/54E Plug-in Unit. Low-Level Differential Calibrated AC Preamp 0.05-10Mv/CM. S/No: 1551.
 
All the above have manuals with circuits. On the odd occasion I have used the 547 oscilloscope. On power up (7/Apr/2013) the oscilloscope triggers and shows the square wave calibration voltage. This is a storage scope with the trace storage being on the screen, not in memory. A sticker on the back states: Calibration Date: 12/11/80. I have not tested the Plug-ins, they look complete except for the 1A7 Plug-in with two disconnected wires. There are no DUT connecting cables.
 
Note, the above equipment is located in Melbourne Australia. Purchaser to pick up or pay for postage/shipment.
 
Please reply off this group,
 
Regards,
 
Roderick Wall.

No virus found in this message.
Checked by AVG - www.avg.com
Version: 2013.0.3272 / Virus Database: 3162/6229 - Release Date: 04/06/13


Coaxial Attenuator Naivete - Please Help

stan_katz
 

I've now learned the hard way that coaxial feedthrough attenuators are not trivial. I thought I could purchase cheap from asia without the seller specifying bandwidth. I wound up with a 10X attenuator that is 10X at ONLY 150khz! The 2X attenuator...only at 50khz. It's almost as if they were notch filters. A disaster. I tracked down an inexpensive domestic source that specified DC - 1Ghz for the same attenuator values. I'm not holding my breath that these will be flat as a board, like branded ones (Tek,HP, Probemaster, et.al) that sell for $20.00 and up on Ebay. I'm also having second thoughts on the asia sourced 50ohm terminator resistors I ordered. If they used spiral cut metal films in them, I've got unwanted inductance there. Even if the resistors are non-inductive, I now realize that dropping a 50ohm terminator on a BNC Tee, and proceeding with a calibration per Tek cal. procedure, could be a fools errand. There will be much more LC due to the connectors and distance from scope input. I need a feedthrough 50hm terminator for serious cal. work. Right? Can anyone point me to a reliable third party vendor of new quality coaxial attenuators that can come in at a price point below $20.00 per connector? In the meantime, I'll be bidding on the name brands, and hoping for the best.

Hope this post helps newcomers avoid my painful lesson.

Stan


Re: Tektronix 7104 and 7D20 showstopping?

Don Black <donald_black@...>
 

Is there a concept book that describes the micro-channel tube and how it works?

Don Black.

On 07-Apr-13 5:23 AM, Craig Sawyers wrote:
 

> Then there is the internal 7104 readout display.
>
> Why does this not burn-out MCP?

It does. That is why the readout intensity knob has an off position, and a
pulsed mode that operates in several ways depending on a range of settings.
If you leave it operating continuously it will absolutely reduce the
sensitivity of the MCP at the readout positions. I have some images in the
pics section of Tekscopes that show an image of a single shot trace at
200ps/div from a TD pulser. Those were taken with a Tek C1002 CCD camera.
The slight graininess of the trace is due to the granular nature of
individual electrons striking the MCP before amplification. It is a helluva
tour de force of analogue scope engineering to do this.

Craig



Re: Handbook of Oscilloscope Technology (.pdf)

Don Black <donald_black@...>
 

If someone has the German version the illustrations could be added to the English translation.


Don Black.

On 07-Apr-13 5:01 AM, Carlos wrote:
 

A little search in bookfinder shows this book was published by Elektor in Germany in 1995 (ISBN 3928051733). The title is Handbuch Oszilloskoptechnik : Schaltungstechnik - Messpraxis - Wartung.

A small photo of the cover is here:

http://www.eurobuch.com/buch/isbn/3928051733.html

It seems this book was published only in German language. I was not able to find it in the Elektor Germany website, so probably is now out of print. However, used ones can be found through bookfinder, although they are not cheap.

However I wonder who did the translation to English uploaded to http://w140.com . Surely it was a lot of work!
Does someone know?

Regards,

Carlos

--- In TekScopes@..., "photo692002" wrote:
>
> An article published in Aug,2012 listed an email address in Vienna
> dr.seibt@... .
>
> Perhaps Fred living next door can try to contact him directly.
>
>
>
> --- In TekScopes@..., "Bhalu" wrote:
> >
> > Hello,
> >
> > Does anyone know where I can find a copy of "The Handbook of Oscilloscope Technology" book/pdf which has the diagrams intact?
> >
> > The version at http://w140.com/Handbook_of_Oscilloscope_Technology.pdf is missing all diagrams.
> >
> > If you have it and can e-mail it to me I will be obliged.
> >
> > Thanks!
> >
>



Re: 7844 saga continues

hpxref
 

"Wow. That could get exciting real quick. That could kill the whole
invertor if it is trying to power a shorted turn in the transformer."
--------------------------------------------------------------------------------------------
Fair comment Craig

Since I had  a couple of 7844 bought as not working a long time ago now,  maybe my efforts
on their EHT repairs may be of interest
Getting into the EHT box is not for the faint hearted on these PSUs as you all know.
One of my 7844's was putting out too little EHT, enough for a badly unfocussed trace, (and give me a nasty jolt)  the other
nothing at all.
But testing the components and transformer normally means just replacing likely bits and then a
lengthy mechanical rebuild of the PSU each time before testing
So how to test the EHT board alone on the bench,without using the 7844 " HV " transformer,
 where everything can be more easily gettable and live monitored?

I removed the EHT board and placed it on the bench, the  HV 7844 transformer board input replaced  by  a handy ferrite
cored xformer from the junk box  wound  "dry" as an experimental eht xformer years ago, then  powered the "primary"  from
a Hi Fi power  amp in turn driven by my function gen on sine out.
Connecting the transformer  secondary to the AC input which normally comes from the 7844 xformer
threaded through the board holes, I adjusted for both frequency and level until the neon stack glowed,
then measured around the multiplier parts with my SMM + HT probe
But  my junk box xformer arced internally and died OC  (It was then  I remembered  why it was in my junk box!)
I then tried a couple of small core power transformers wired back to front, "secondaries" in series
and "primaries" (12v) in parallel and drove it from the same source again.  Much lower frequency when
tuned to "sweet spot" resonance under 7844 EHT board load, and more ripple, but still
worked well enough at some k/Hz input to trouble shoot the EHT board and multiplier
This found both a faulty rect diode (tested OK on a hi reverse  R tester, but still bad) , two leaky HV caps a faulty
neon and a  high resistor (measured OK cold, but going high when powered)

Since most of us have, or can get small power transformers, some may find this a useful approach.
Having 240V ac line helped as the xformers have double the Vout than 115 line ones, but just use more of them.
NOTE: Th old  HI FI power amp (35W RMS) I used had a built in  auto shut off circuit to switch off the output if output current was exceeded
and this is likely necessary due to the complex impedance's of the paralleled transformers being lower than the 8 ohm Z out
of the amp and of core saturation if the combo  accidentally driven too hard)
The HI FI amp was used as the output from my audio/funct gens had too low drive power to push up the EHT

But the repair or checking of the boards was made much easier by doing it this way, and well worth the set up effort.
Note that power transformers in this country were mandatory  flash tested at a couple of kV or so  before they could be sold publicly  and , from memory, the ac input from
 the rigged up combo was around 750v ac into the 7844,card  but my notes of 3 years ago are not to hand and ime relying on a fading  memory for this
Whatever it was the combined V multipliers did give me enough EHT dc out to check everything on the card, even if not at  full 24kV EHT
 I  would have  multiplied  the ac input by the cards combined multipliers  to roughly get a dc EHT out which corresponded fairly well with that ratio and into the 20kV region
I used an EHT probe both as a load and to monitor EHT output, the light load this gave probably allowed the final multipliers to give
a good output with the low multiplier capacitor values at the lower frequencies "inputted"
Although not tried its possible that a quality  old tube type HI FI audio output transformer wired back to front should  be even better
as its frequency response may extend to the actual 7844 PSU frequency (24khz?) put out by its psu and its step up ratio even higher
Filed away on a cd backup somewhere are some digital photosI took of the  of the set up.
If of interest should I  track them down and post them?

John Byers



Re: Planning 2467B LVPS re-cap

vdonisa
 

More trouble: I found out my A2 board has 3 x 1uF/50V unpolarized while the manual I have mentions only 2.

Here is a photo which shows a close pair of them while the manual indicates only 1 at that location:

http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/221122190/view 

The third one can be seen in the previous photo in the album (located according expectations).

The next photo shows the whole mystery A2 board.

In addition I noted that the area around Q1351 has a brown coloration from heat. Is this common or should I investigate for something defective there? If it's common, can that transistor be helped with some small heatsink? Anyone that has done such mod?

Thanks,
Valentin


Re: Planning 2467B LVPS re-cap

vdonisa
 

Hi Patrick,

It is difficult to tell exactly but I'd say around 12 caps were replaced in total on both boards. Some of them were easy to tell (Chong and Sanyo brands) the others are Nichicon and United Chemi, some of them may be originals but most likely not. The only ones I could swear to be originals were 3 green Nichicons, the 2 big blue Spragues, and all the small Nichicon VX.

There were 4 Chongs in total (2 on reg board 2 on inverter board), they were meant to replace some original 100uF/25V ones, and the Chong is rated 100uF/50V. Theoretically it should be OK, and they would probably had worked fine in many other applications (linear PS, stereos etc), but switching power supplies is one the toughest place to be as a capacitor. I'm replacing all 100uF/25V with Panasonic 100V/63V EEU-FR as we're speaking, if those won't last then at least I'll know that I've tried :-)

Anyway I'm going through it slowly, comparing at each step the boards with the manuals and with pics I've downloaded from the net, so I hope I won't do any blunder.

Thanks!
Valentin

--- In TekScopes@yahoogroups.com, "Patrick Wong" <patwong3@...> wrote:

Hi Valentin,

1. Have you been able to determine how many capacitors had been previously replaced?

2. Do the Chong capacitors lack uF and voltage rating labeling?

I have "before" photos of my 2465A power supply which shows the original caps. If those would be helpful, I could post to your album.
Thanks,

Patrick Wong AK6C

--- In TekScopes@yahoogroups.com, "vdonisa" <vdonisa@> wrote:

Thanks you gents! I just discovered that one of the existing capacitors had leaked electrolyte, picture added to the gallery:

http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/1955\;
338772/view
<http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/195\;
5338772/view>

Will keep you updated with any new findings / questions :-)

Thanks,
Valentin VE3VDO


Re: Planning 2467B LVPS re-cap

honolulusnowwhite
 

Hi Valentin,

1. Have you been able to determine how many capacitors had been previously replaced?

2. Do the Chong capacitors lack uF and voltage rating labeling?

I have "before" photos of my 2465A power supply which shows the original caps. If those would be helpful, I could post to your album.
Thanks,

Patrick Wong AK6C

--- In TekScopes@yahoogroups.com, "vdonisa" <vdonisa@...> wrote:

Thanks you gents! I just discovered that one of the existing capacitors had leaked electrolyte, picture added to the gallery:

http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/1955\;
338772/view
<http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/195\;
5338772/view>

Will keep you updated with any new findings / questions :-)

Thanks,
Valentin VE3VDO


Re: Planning 2467B LVPS re-cap

vdonisa
 

Thanks you gents! I just discovered that one of the existing capacitors had leaked electrolyte, picture added to the gallery:

http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/1955338772/view 

Will keep you updated with any new findings / questions :-)

Thanks,
Valentin VE3VDO


--- In TekScopes@..., "Patrick Wong" wrote:
>
> Hi Valentin,
>
> I agree with Tom J regarding #2 and did not replace that capacitor.
>
> Regarding #1, my personal inclination would be to either replace with the correct 1 uF 50V non-polarized capacitor or else leave those two caps alone. It doesn't appear that either is in a highly stressed position.
>
> However I can't offer a specific reason not to use a polyester or ceramic capacitor.
>
> Patrick Wong AK6C
>
> --- In TekScopes@..., "Tom Jobe" tomjobe@ wrote:
> >
> > Hi Valentin,
> > My knowledge is not sufficient to even venture a guess on question #1, but I have not seen any discussion of question #2 as being a problem... so I would leave C1065 as it is.
> > tom jobe...
> >
> >
> >
> > ----- Original Message -----
> > From: vdonisa
> > To: TekScopes@...
> > Sent: Saturday, April 06, 2013 5:35 PM
> > Subject: [TekScopes] Re: Planning 2467B LVPS re-cap
> >
> >
> >
> > Sorry gents I did a mistake while reading the Nichicon PW datasheet, the max ripple is actually only 0,07A not 0.7A so there's no contest with the CA series.
> >
> > However I'm still looking for an answer to my first 2 questions ;-)
> >
> > Thanks,
> > Valentin
> >
> > --- In TekScopes@..., "vdonisa" wrote:
> > >
> > > Hi Tom,
> > >
> > > I just checked. The negative terminal of the smaller black cap on the left in the photo is connected to ground. While the taller cap behind has neither pin connected directly to ground. So the arrangement as in the picture is correct. It is the diagram I have that shows them reversed (wrong).
> > >
> > > Two questions that came to my mind while examining the boards and schematics:
> > >
> > > 1) For C1274 and C1291 (originally unpolarized 1uF/50V electrolytics) is there any reason I would not want to use X7R dielectric ceramics (with +- 15% capacity variation over -40 + 125 Celsius temp range?) I know I shouldn't use them in frequency filter / timing circuits, but in the Tek circuit some variation of capacity with temp/voltage doesn't look very harmful (they look more like having a decoupling function there); polyester film caps should definitely work there from an electrical pov, however I'm not sure that I can find them with acceptable pin spacing. (My plan A is use polyester if it fits mechanically if not plan B & C are investigate ceramics or order non-pol electrolytics)
> > >
> > > 2) C1065 doesn't look stressed, has no visible damage and is not in a safety role, is there any reason I would need to replace? (i.e. are there some horror stories about a bad batch of them or something like that)
> > >
>


Re: Mild OT question – Checking diodes

Bob Albert
 

Like anything else, the test is worth something as long as you know the parameters.

The DMM test sends a current through the diode and measures the voltage drop.  It's not a complete test by any means.  If you want something better, you need to do a more sophisticated setup.

For me, almost always, a simple ohmmeter test with a VOM, first one polarity and then the other, serves very well.  If it's a high frequency signal diode, that may not be a good test.  If it's a zener, one needs to break down the junction with a specific current and measure the voltage.

No substitute for knowing what you are doing.

Bob


--- On Sat, 4/6/13, Robert wrote:

From: Robert
Subject: [TekScopes] Mild OT question – Checking diodes
To: TekScopes@...
Date: Saturday, April 6, 2013, 12:38 PM

 

Had this thought reading Craig Sawyers 7844 repair work:

Recently working on a 485, I used a simple diode curve trace set up. One of the diodes clearly showed bad, probably leaky. Initially that diode would still show some forward reverse difference on a DMM diode test. Does this seem reasonable? I am beginning to doubt the DMM diode test, or if I use the DMM test correctly.

Bob

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