Date   

Re: TDS544A status

Ed Breya
 

Now I'm getting paranoid - I just remembered that lately the 754A display sometimes has slight flickering in the display shortly after power-up, and then would be OK after warming up a bit. I hope this is not a sign of impending doom like a flaw in the HV transformer that gets worse as happened in the 544A. I'm thinking about maybe opening it up to see if there's any evidence of HV leakage on the outside of the transformer.


Ed


Re: TDS754A printer compatibiliy

allanjamison
 

Ed:

I have a TDS 544A and it has a centronics parallel port. I have used it with several printers that use the standard HP PCL language. Set the printer options to output to the centronics port and select the laserjet format.

It should work. The PCL format uses ASCII characters and it a very common standard in the older, more expensive printers, from many vendors. Many current printers also support PCL but you have to check the specifications. Very inexpensive printers now do most of the formatting in the PC and require proprietary drivers.

I hope this information helps. I am assuming the your TDS 754A has similar options.

In my TDS 544A there is also a floppy disk that you can use to save standard image formats. These formats can be processed by most PC drawing and word processing programs. That is another way to get a screen print into a document or print it out.

Al Jamison


Re: 7603 Strange HV Need Help

Ed Breya
 

Yes, the sockets can cause much more grief in terms of diagnosis and repair. I was thinking more in terms of frequency of occurrence - I've seen way more stories about bad caps, although perhaps sockets actually are the cause of more trouble than is attributed to them.


Ed


Re: 7603 Strange HV Need Help

 

I would actually rank the TI sockets as a larger problem than tantalum
capacitors. The capacitors unambiguously fail and are relatively easy
to find and replace. The sockets become intermittent with no visible
sign and replacing them is a much more involved procedure.

On 21 Jan 2016 14:21:24 -0800, you wrote:

The problems with TI sockets and ICs with silver plated leads are well known, and have been discussed here a number of times over the years. Unfortunately, Tek used a helluva lot of them in many of our favorite instruments from that era. I believe they are one of the main causes of problems - especially strange and intermittent ones. I'd rank the TI problem well below the usual bad Ta caps and worn out Al caps, but it's up there somewhere near the top of the list.

Ed


Re: 7603 Strange HV Need Help

 

I have never encountered this problem with silver or these TI ICs of
which I have lots but I have with thick gold. I assume the leads are
FeNi42 which was a common lead frame material in the past and whatever
process which is needed to plate silver to FeNi42 was lacking.

Maybe silver sulphide which is that black tarnish you find on silver
can form between the lead frame material and the silver isolating it.

On 21 Jan 2016 15:42:36 -0800, you wrote:

In a nutshell, there is something seriously galvanically and/or metallurgically wrong with those TI IC leads with Ag plating. Over time, and depending on the environment, the bond between the Ag plating and whatever is underneath disintegrates, literally disconnecting the outside surface from the leadframe material, causing loss of contact. I have even seen this in leads that were soldered to the board clean through.

Ed


Re: 7603 Strange HV Need Help

Ed Breya
 

In a nutshell, there is something seriously galvanically and/or metallurgically wrong with those TI IC leads with Ag plating. Over time, and depending on the environment, the bond between the Ag plating and whatever is underneath disintegrates, literally disconnecting the outside surface from the leadframe material, causing loss of contact. I have even seen this in leads that were soldered to the board clean through.


Ed


Re: TDS544A status

Ed Breya
 

OK - message sent.


7834 Transformer rewind

Gordon <tekscopes@...>
 

Hi all. The 7834 transformer has been running for a couple of days now and appears to be OK. I just thought I'd post some details. The first attempt blew through the windings. One of the issues with layer winding as opposed to bank winding is the way Tek anchored the HV winding tails. They use a small circuit board to fix the fine ends and the Teflon output wires. The problem with layer winding and the circuit board is that the start has to come up and over the return of the second layer which is at about 1400V. You can insulate it but the potential for a flash over is higher. It doesn't happen with bank winding as the high voltage end is always at the opposite end to the low voltage.

The second attempt didn't blow but the voltage was too high, it wouldn't regulate. There really could only be two reasons why output > input * turns ratio. I'd got the turns wrong or it was resonating. I was a little skeptical about the distributed capacitance causing resonance. Whilst I could see it would be critical in a tank circuit, why would it make that much difference in what is really just a transformer? I'd fairly good reason for the line of thinking. The reason I have a coil winder is from my guitar pickup winding days. I know from past experience and data that a guitar pickup capacitance is in the order of 100pf. They vary a lot but 100pf is not untypical. This is for a coil of circa 8000 turns single insulated 0.063mm polyurethane. Just how much capacitance could a 610 turn coil have? Prepare to be amazed, at least I was.

Thinking I must have got the turns wrong I wound a third coil. No change so it had to be distributed capacitance. The thing self resonated at 25k - how convenient! It's the working frequency of the switcher.

To get a grip on how the coil could be wound to reduce the capacitance I did a series of simple winds.

455 turns 0.08mm (~40AWG) in two 25mm layers on 19.6mm piece of wood dowel. In the following when I say insulation I'm talking about insulation between the layers. There were odd bits of Kapton to hold things in place. 'Return wound' is where at the end of a layer the wire is brought back over the wind so that the layer starts are always at the same end. I'm not sure of the proper name for it.

I used the two capacitor method for measuring, there's an on line calculator here http://www.vk2zay.net/calc/DistributedCapacitance. There are others but they give the same result.

Single build solderable polyurethane, no insulation = 953pf

Single build polyester, no insulation = 634pf

Single build polyester return wound, no insulation = 335pf

Single build polyester 1 layer 5 mil Formex insulation = 78pf

Single build polyester 1 layer 10 mil Formex insulation = 33pf

Just as a sanity check I checked an old guitar pickup I had lying around, IIRC 7650 turns single build 0.063mm polyurethane - 76pf - go figure?? As a double sanity check I redid the first test and got the same result.

Given the massive difference the insulation makes I used solderable Polyurethane for the final 610T HV wind. I'm not keen on scraping these fine wires. All others were single build Polyester.

I managed to get some Micanite but it might actually be better using Formex, being polypropylene it has a lower dielectric constant than Micanite. The downside is that it won't stand much heat - working temperature of 115°C. Lets hope it's enough. The good thing about flexible Micanite is that it stays formed. Once you've wrapped it round it more or less stays there. The 0.01" Formex is quite springy, it needs holding down quite well with tape.

I dispensed with the little circuit board Tek used and fixed HV Teflon wire to the coil ends. This brings it's own problems, anchoring them sufficiently to prevent them being yanked out. I soldered the ends to a small (about 5*5mm) square of copper tape and used that as the anchor on top of some Kapton. The copper tape sticks like the proverbial so it should be OK. Small bits of Tape don't stick that well to Micanite. If you tape over Micanite make sure it goes all the way round so the tape sticks to itself.

There are some shoulders of insulation on the original. Presumably to support the bank wind. I put them on but wouldn't if I was doing it again. Ideally the between layer insulation needs to be wider than the coil. If there are shoulders there you can't really do that with 10 mil insulation. Another problem with using thicker insulation is that you can't slit the edge and slip it over the start of the return wind. It would probably weaken the wire, that's if you could manage to do it. I got round it by leaving a gap of about 1.5mm in the insulation over the width of the coil with a piece of Kapton under the gap.

I also finished the second layer of the HV winding 4mm short of the end. I've uploaded a drawing here http://www.mgcsoft.com/tek/7834_hv_transformer_drawing.pdf. I didn't stick exactly to the original drawing mainly because tape is much easier to get here (UK) in metric widths. Some of the insulation lengths on the drawing may not be exactly right after the bifilar winding. I'm not about to rewind it just to check the lengths!

I found it easier to take the taps out to the right hand side then bring them back to the left once the wind was finished. If you take them to the left/insulate then wind on top, it's harder to get the continuing turn to lay properly. I'm guessing it's how seasoned winders do it anyway.

On the drawing it specifies to "Fold back wires 1,4, 5 and 6, I didn't. It's probably for strength and easy enough if you're using a hot chemical stripper. If you're scraping you have to separate the wires, then you don't know which is 'live'. It's not a problem with single wires if you're careful.

When you come to fit the transformer the wires are conveniently 1:8 left to right as you look at the back of the board with the transformer on top.

It's quite easy to check the HV wind without finishing the transformer. Do the bifilar wind which is relatively easy. Put the coil onto the core and drive the bifilar wind with a 50Ohm sig gen at 25kHz. No need to run it at full voltage, 1V will do. I don't know whether it's necessary but I tacked a 3.3M resistor load onto the 610T wind. If Vout > Vin*turns ratio you have a problem which is likely to get worse when the other winds are done.

A small point but the original drawing for the transformer is wrong. It's been corrected, sort of in the change log. The change log extends wire (4) to 1"3/8 because it was too short. What should have been done is to reverse the lengths 1:4 they should be 1=1", 2=1"1/8, 3=1"1/4, 4=1"3/8. They're the other way round on the drawing.

Sorry about the mixed units. My brain works pretty much the same way - mixed :-)

Cheers

Gordon


Re: TDS544A status

stefan_trethan
 

Charly is c.dickens@xs4all.nl
or if yahoo tries to mess with it again:

c.dickens at xs4all.nl

ST

On Thu, Jan 21, 2016 at 11:34 PM, edbreya@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:
I'm not sure what you mean:


"hi Ed please send me an email I have the same unit TDS544A and calibration software. now I can buy a TDS754D processor fail. send me email please: c.dickens@... mailto:c.dickens@...


please email me.
greetz charly "



I can't send emails directly to anyone in the group because the address is blanked. I think you can email to me at my user name at yahoo.com.


Ed








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Re: TDS544A status

Ed Breya
 

I'm not sure what you mean:


"hi Ed please send me an email I have the same unit TDS544A and calibration software. now I can buy a TDS754D processor fail. send me email please: c.dickens@... mailto:c.dickens@...


please email me.
greetz charly "



I can't send emails directly to anyone in the group because the address is blanked. I think you can email to me at my user name at yahoo.com.


Ed


Re: 7603 Strange HV Need Help

Ed Breya
 

The problems with TI sockets and ICs with silver plated leads are well known, and have been discussed here a number of times over the years. Unfortunately, Tek used a helluva lot of them in many of our favorite instruments from that era. I believe they are one of the main causes of problems - especially strange and intermittent ones. I'd rank the TI problem well below the usual bad Ta caps and worn out Al caps, but it's up there somewhere near the top of the list.


Ed


Re: TDS544A status

bddicch
 

hi Ed please send me an email I have the same unit TDS544A and calibration software. now I can buy a TDS754D processor fail. send me email please: c.dickens@xs4all.nl


please email me.
greetz charly


Re: TDS544A status

Ed Breya
 

The old caps are gone, the board's washed, and it's all back together except the display is disconnected. I have it running now for another burn-in to dry out any residual moisture. BTW it seems to run fine without any electrolytic bypass caps on the acquisition board - the ceramic ones all over the place should take care of fast stuff, but there could be slower stuff and supply ripple that may cause various issues under some conditions. If I re-commission this scope, I'll put in the Ta replacements.


I counted the husks after ripping them all out - 68 of those caps were on there. My previous mention of 90-something must have been the total estimate for the whole scope, so not as many left to replace as I thought - yippee.


Ed


Re: 7603 Strange HV Need Help

 

"But 2 of the biggest blunders came from TI. One was silver plating on
7400 series chips and the other was edge contact IC sockets."

What is wrong with silver plating IC leads?

I thought they were using Kovar for the IC lead frames back then but I
guess it was NiFe42 or something. Maybe Kovar was used with ceramic
packages?

On Thu, 21 Jan 2016 08:21:42 -0500, you wrote:

Huh?

Jerry Massengale

-----Original Message-----
From: David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com>
To: TekScopes <TekScopes@yahoogroups.com>
Sent: Thu, Jan 21, 2016 2:04 am
Subject: Re: [TekScopes] Re: 7603 Strange HV Need Help

What is wrong with silver plated kovar leads?

On Wed, 20 Jan 2016 08:58:21 -0500, you wrote:

Hi,

As a 30 year Texas Instrument engineering tech I took a lot of pride in my company and the engineering work we did. But 2 of the biggest blunders came from TI. One was silver plating on 7400 series chips and the other was edge contact IC sockets. You put an old 7400 IC in an old TI socket and you have trouble.

Jerry Massengale


Re: TDS544A status

stefan_trethan
 

Best to consider yourself lucky that the burn-in did not turn into a
burn-down during the night.
The CRT on my TDS544A isn't very bright either, especially if you work
all 4 traces you can hardly see some colours.
The best repair would be to fit an LCD screen, but not very cheap.

Definitely take those caps off and wash the ACQ board. If nothing else
you can make someone happy in the future.



As an aside, it is a bad idea to run a board with electrolyte leakage
at all. Electrochemical corrosion makes the problem worse.

ST

On Thu, Jan 21, 2016 at 7:28 PM, edbreya@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:
Oh well, this one's a goner as far as being a stand-alone scope goes. The burnt part is the HV flyback transformer T120. Upon opening it up it was obvious there was a charcoal patch on the top where it was arcing. It looks like it had internal failure, then burned up enough to also arc to the core. To confirm, I propped it open enough to observe, and rigged up enough connections on the control board to provide power to the display. It immediately lit up on power-up, and looked like a miniature charcoal BBQ glowing away. This transformer may have been on its way out for a while. As I reported at the very beginning, the display was quite dim, but I cranked up the internal intensity and contrast tweaks to get a decent display. This one extra night of continuous running was probably enough to finish it off - I never ran it so long before.


At least it was easy to find the problem. It's not worth fooling around with any more, so I'll set it aside - the CRT and shutter can be saved as spares for the 754A, and if I ever need it as a scope it can still work with an external VGA display, like in a dedicated rack mount setup. If I happen to find a junker for cheap that's ruined because of the bad caps, but has a good display, that may work out too, but not worth worrying about now. Even so, it still needs all those bad caps replaced on the acquisition board. I may just strip them all off and wash the board to prevent further damage, and set it aside for future consideration.


Ed






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



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Re: Cathode supply voltage tolerance

Gordon <tekscopes@...>
 

On 21/01/2016 18:24, kjohnson25@tampabay.rr.com [TekScopes] wrote:
I completely stripped the defective transformer down to the core and rewound the entire transformer.
It works perfectly now. I'd be interested in sharing thoughts with you about the process you used and what materials you used. I'd be willing to share my techniques and materials with you also.
I remember. I'll post details in a new thread with an appropriate subject line. I've some interesting numbers regarding different winding/insulation methods.

Cheers

Gordon


Re: TDS544A status

Ed Breya
 

Oh well, this one's a goner as far as being a stand-alone scope goes. The burnt part is the HV flyback transformer T120. Upon opening it up it was obvious there was a charcoal patch on the top where it was arcing. It looks like it had internal failure, then burned up enough to also arc to the core. To confirm, I propped it open enough to observe, and rigged up enough connections on the control board to provide power to the display. It immediately lit up on power-up, and looked like a miniature charcoal BBQ glowing away. This transformer may have been on its way out for a while. As I reported at the very beginning, the display was quite dim, but I cranked up the internal intensity and contrast tweaks to get a decent display. This one extra night of continuous running was probably enough to finish it off - I never ran it so long before.


At least it was easy to find the problem. It's not worth fooling around with any more, so I'll set it aside - the CRT and shutter can be saved as spares for the 754A, and if I ever need it as a scope it can still work with an external VGA display, like in a dedicated rack mount setup. If I happen to find a junker for cheap that's ruined because of the bad caps, but has a good display, that may work out too, but not worth worrying about now. Even so, it still needs all those bad caps replaced on the acquisition board. I may just strip them all off and wash the board to prevent further damage, and set it aside for future consideration.


Ed


Re: Cathode supply voltage tolerance

karin_k3uu
 

Hi Gordon:
I noticed you inferred that you re-wound the 7834 HV transformer. About a year ago I did a similar project
by rewinding the HV transformer on a 7934. The original transformer developed a short in the HV winding which is located closest to the core. The HV transformer for 7834 and 7934 are essentially the same.
I completely stripped the defective transformer down to the core and rewound the entire transformer.
It works perfectly now. I'd be interested in sharing thoughts with you about the process you used and what materials you used. I'd be willing to share my techniques and materials with you also.

Regards,
Karin Anne Johnson
Palm Harbor, FL


Re: letter from 'Tim Speed'

Dave Casey <dcasey@...>
 

I've gotten both of those, but they're getting caught by my ISP's spam
filter.

Dave Casey

On Thu, January 21, 2016 7:47 am, Dwayne Verhey yg@verhey.org [TekScopes]
wrote:
I got another variant today ("Your Telephone Bill Invoices & Reports").
As no-one else here has mentioned getting one, the source is probably
not another member of this list after all. I'll be creating a new e-mail
address and dumping this one.



On 21/01/2016 6:45 AM, geoffrey thomas geoffreythomas@onetel.com
[TekScopes] wrote:

This trojan is in the news today :


http://www.theregister.co.uk/2016/01/21/bronzeplaced_malware_belting_bu
rsting_british_business_bank_accounts/

Geoff.


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Re: TDS544A status

Ed Breya
 

I let it run all night for burn-in testing. It was just fine first thing this morning, then a little later I noticed no display and that smell of a burnt part. I thought one the replacement caps failed, but it looks like something in the display unit went out instead. Running it with external VGA, it said POST was OK and ran as usual, so I'll have to dig into the display next.


Ed

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