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Hi Colin,
Those 7CT1N captive leads are problematic. I've fixed several 7CT1Ns and they almost all had bad cables. By now most of insulation on the cables has gotten brittle and is cracking. The plug on the end gets banged around and twisted and/or bent which stresses the strands inside until they start breaking. I don't think the design engineers realized they would have a 50+ year useful life.

Somewhere along the way I realized I was going to need those cables. I think I bought a bunch from Deane Kidd but it was so long ago that I can't recall where they came from for sure.

Esmond's replacement cable is on the way to him.

Dennis Tillman W7PF

If I had that need abd that concern, I’d mill some wooden blocks to temporarity replace the feet and store the original feet away.

DaveD

Sent from a small flat thingy

Hi All!
I've got a bare 7704 frame that's in the way, and I'd like to reposition it from the vertical, to the horizonal, to store it.... "upending" it, so to speak. I'm a little leary of doing it... because I think those plastic feet, and rubber pads, on the back, might not hold out, in the long run.
Best regards and wishes.
Roy

, here is a good informative video on capacitors if anyone is interested

Thank you Chuck for the reply, I am trying to avoid electrolytic capacitors when possible.

I just took apart the HV XFMR from my 561. The core is a ferrite or powdered iron E-E type. After removing the wrap around the core, the two E's separated easily at room temperature.

Still hoping someone has the winding data for a 120-225 or a 120-275 transformer. That data might confirm my reverse engineering of my 120-225.

There appears to be two variants of this captive lead. The picture in my manual shows an in-line white plastic "plug", as does Tekwiki. It is given as p/n 195-0095-00 "Lead, test: BNC" and the manual also lists p/n 348-0301-00 "grommet: plastic, 0.312 ID x 0.43 inch OD" associated with the lead. However, my 7CT1N has a black lead with a double-ended connector forming a tee with the lead. One end mates with a BNC male, the other with a BNC female, but still only one connection, no shield. I might add that I purchased the 7CT1N from Dennis Tillman about a year ago.

Colin.

Thanks Miguel,

That's what I was looking for - the info is now saved in my 576 notes.

I like that little HV transformer in the picture. It's a fine example of a common method of attaining good HV performance by stacking the sections of winding. If one could be found in the right size range, and with a primary that can be readily modified, it may be the ideal solution for a drop-in replacement.

This same sort of HV structure is used in transformers for LCD CCFL running, and in laser printer toner charging, etc. None that I've seen look quite "right" for a single-piece replacement, though. The next closest thing would be a two-transformer combo - a low voltage one for making the raw HF power and +225 V, and a small HV type that can tap the HF power and scale it up to the proper 4 kV range. With lots of winding flexibility in the first transformer, it should be doable, and attain the proper ratios and voltage regulation. I estimate that the +225 V and 4 kV each need about half of the total output power available - about 3W each.

Ed

576 Transformer
Inductance Resistance AWG mm Turns AL=L/N^2
Pin 2-3 305,0E-6 22,0E+0 25 0,45 26 451,2E-9
Pin 7-8 918,0E-3 85,0E+3 40 0,08 1400 468,4E-9

Transformer core size
50mm
13mm
31mm

Inductance 1khz 1mA

2-3 305uH 22R
7-8 918mH 85K

Rubber potted

/g/TekScopes/album?id=94656

I have the idea to use a pre made transformer and rewind it, reusing the HV coil. Something like this:




But I think that’s is a little bit smaller.

Regards

Miguel





-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Ed Breya via Groups.Io Enviado el: miércoles, 28 de agosto de 2019 3:40
Para: [email protected]
Asunto: Re: [TekScopes] Tek 576 Curve Tracer HV Transformer winding

Has anyone measured the low frequency (like 1 kHz) primary inductance of a normal, OK 576 HV transformer? I looked at the data sheets (at tekwiki) on the part, and none appear to show any inductance value. I've been pondering possible alternate solutions to the "bad epoxy" transformer problem. The first is a drop-in two-transformer (one to provide the HF power and +225V, the other to make the HV) scheme, to sub for only the original transformer. The other is a replacement for the HV supply section, basically an independent SMPS that can run from the +100V supply, like the original.

My 576s are good, with the newer "black" transformers, but all the recent talk got me interested, and revisiting ideas I've been thinking about over the years.

In case anything major should happen to the HV transformer or HV guts, I'd like to be ready to fix it, without resorting to rewinding the HV transformer. In either scenario, the plan is to use a "modern," off-shelf type small HF-HV transformer to provide the 4 kV. I'm picturing the little kind commonly used in Royer converters for LCD CCFL backlighting. I have many dozens of all sorts of these things. I'm sure that some types are just right for this particular setup, but would need a lot of experimenting to figure out.

Anyway, if anyone has more info on the original transformer, please let me know.

This is a low priority project, but I like to think about it. If I ever get around to actually making it, I'll put up the how-to info.

Ed

/g/TekScopes/photo/86536/0?p=Created,,,20,2,0,0

I included a picture from the service manual of the floating power supply that involve these capacitors

I'm troubleshooting a noisey step generator, when I turn the step generator off I don't get any flickering noise artifacts on the display. I figure as the first step is replace any old electrolytic capacitors and tantalum capacitors as I don't own a ESR meter to check them.

Upon further study I found C391 C393 come off a floating power supply in the the step generator circuit

The only reasons I use an oven over the water
technique (aka teacup method) for a couple of
simple reasons:

1) it seems less likely to burn me. Water soaks
through my leather gloves, and it gets hot quickly.

2) Businesses have strict rules about what they can
dump down the sink. Since they would have to prove
that the water carried nothing dangerous, I prefer
to avoid the issue... and use air.

-Chuck Harris

Miguel Work wrote:

Thanks Chuck!

I put transformers in boiling water some minutes, with the same results

Regards

Miguel


-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Chuck Harris
Enviado el: miércoles, 28 de agosto de 2019 18:36
Para: [email protected]
Asunto: Re: [TekScopes] Tek 576 Curve Tracer HV Transformer winding

Having done hundreds, I find removing the core to be very simple.

1) remove any tape, clips, clamps, etc that are holding
the core halves together.
2) heat the core to 130C in an oven. There should be no
smell to speak of.
3) using gloves, grab the top core with one hand, and the
bottom core with the other, and twist so that the faces
of the core shear their glue.
4) use a knife to scrape the excess glue off of the core
faces, and anywhere else it annoys you. Keep the core
hot for this operation.

And you are done.

I have never had to put any great effort into this process.
It happens very easily, and non destructively... .The coil and its terminals come free, and could be put back together if you wished.

-Chuck Harris

ulf_r_k via Groups.Io wrote:

Yes, if you can make them fit.

Are the electrolytics bad? If not, I would leave them
alone.

-Chuck Harris

DW wrote:

Having done hundreds, I find removing the core to be
very simple.

1) remove any tape, clips, clamps, etc that are holding
the core halves together.
2) heat the core to 130C in an oven. There should be no
smell to speak of.
3) using gloves, grab the top core with one hand, and the
bottom core with the other, and twist so that the faces
of the core shear their glue.
4) use a knife to scrape the excess glue off of the core
faces, and anywhere else it annoys you. Keep the core
hot for this operation.

And you are done.

I have never had to put any great effort into this process.
It happens very easily, and non destructively... .The coil
and its terminals come free, and could be put back together
if you wished.

-Chuck Harris

ulf_r_k via Groups.Io wrote:

Really the question is can I substitute film capacitors for electrolytic


I notice there are 2 electrolytic capacitors C391 C393, 15uF 100V, would this film capacitor work () as a drop in replacement?

Apart from the TEK Xfmr specification and the recently
published ferrite core specification, I have not seen
any additional information about this transformer.

I would say that the most critical part of rewinding
it is splitting the cores under heat. The smell from
the brown epoxy was not very pleasant but could be dealt with
but cracking the core halfes is a show stopper.

The good part is that there is no CRT blanking so there is no need
for multiple windings. Once a bobbin has been obtained
and the cores has been split there is nothing to loose
but a few hours of tedious careful winding...

If the rewinding had gone bad, I would have gladly payed
$200 for a professionally wound transformer had there
been a "group purchase".

Some other comments from memory:

The HV transformer was not the only problem with my
576. When repairing the PSU, I checked a number of the
AllenBradley carbon composition resistors used.
Many of them had drifted out of their tolerance.
If a problem develops maybe they should be checked.

Some of the electrolythic capacitors needed to be replaced.
Be careful with C708 (2.2uF) of the -75V supply.
It is necessary for this to be a low leakage type
as this voltage serves as a reference for some of the other
voltages.

The power semiconductors on the rear metal frame are
a number of TO-3's. Some of the protective caps had cracks
in them, which made the screws loose and caused
the thermal resistance to increase
between the TO-3 cases and the instrument frame.
They should all be checked.
Cheers
Ulf KylenfallSM6GXV

Randy,

You have to rid yourself of that crutch quickly, as it isn't
really a crutch, but rather a hobble.

Every part you change comes with the risk that you will do it
wrongly, and add another thing to fix...

The rub is, that once you replace a part, your mind won't let
you look there again, as it has to operate under the belief
that you did the replacement correctly, or it will be stuck in
a loop.

Replace only the broken parts, until you have fixed the supply.

After it is fixed, you may want to update some of the risky parts,
you might not.

I always have a good reason for each part I replace. Sometimes
it is wrong, but never is it done without serious thought.

If the part isn't bad, put it back. Otherwise you are adding
another variable to an already complex equation.

-Chuck Harris

randolphbeebe@... wrote:

Troubleshooting linear power supplies:

Is about the simplest job out there... possible testing light bulbs
in a lamp is easier, but the technique is still the same.

Start with your symptom:

If it is *no* power on any output, go to the other end, where the power
comes in, and work your way across until you find something that isn't
right:

1) power mains good?
2) power getting into box?
3) power getting past fuse and switch?
4) power getting to transformer?
5) power getting out of transformer?
6) power getting through bridge rectifier?
7) power getting to filter capacitors?
8) power getting to regulator
9) power getting out of regulator
10 power getting to output terminals

If there is correct power on some outputs, and incorrect output on others,
work from the output that is bad until you find good power.

1) power getting to inside of terminals?
2) power getting out of regulator?
3) power getting into regulator?
4) power getting to filter capacitors?
5) power getting to bridge rectifier?

That is all troubleshooting linear supplies is.

You don't need anywhere as much hand holding as you think you do.

As to exact voltages, that is rarely beneficial. You need to understand
ranges of voltages that are appropriate to the device you are looking at.

If the supply should be putting out 15V, then you expect 15V out of the supply,
and somewhere between 2 and 10 V going into the regulator.

Transistors never have more than 1V base to emitter in the direction the arrow
points on the emitter, or they are bad.. and current goes from + to - . In
the opposite direction, the transistor is off, and dead if it is above about
6 volts (reversed).

OPAMPS that have negative feedback (most) must have zero volts between the
"+" and "-" input, or their outputs will be stuck on a power rail... or they
are broken.

Power supplies are made up of a few dozen little jobs each like checking a
light bulb.

-Chuck Harris


daven9ooq via Groups.Io wrote:

Albert,

I printed out your previous replies for my future reference. The reality is that I do not fully understand the circuit logic on this scope which is why I am not too effective at diagnosis. You not only helped me isolate the problem but walked me through the diagnostic process which will help me in the future...,many thanks!

I started this hobby only recently and am impressed at how many guys are willing to share their hard won knowledge and time.

As for needless component replacement, it is the crutch of the neophyte. The only positive outcome of all that extra work is the super-clean DC power now powering the scope:-) .

Best,
Randy

Hi, John, Wow you really want to make me work hard , but I understand your logic, Which is the proper procedures to troubleshoot any piece of equipment.?
This should help any one of us who are new or less experienced.
To try to answer some of your questions Yes I did print out the schematic? and I even printed out datasheets for all the opamps, but no I did not enlarge it, I have a magnifying lamp ,I dont have any way to print anything larger than 8.5x11 .
Yes I did check the transformer, that is to say I? measured ac voltage at the secondary for the 2 variable supplys,? to be honest I did not write it down on the schematic, and I dont recall what it was exactly, For the sake of thouralness I will go back and do this over, but if you read my earlier posts , what is the point of doing steps 1-5 if I measure + and - 15volts at both references??
This is a multi tap transformer with no less than 10 secondaries, all terminated with connectors , I'm using pieces of stiff wire or paperclips to get into the connectors and jumpers to my probes, and there are 7 full wave bridge rectifiers?
I did look at the waveform of the two variable supplies ,they both looked good,? I did not check the ripple as I just finished a full recap!
Back to the transformer, the first thing I do when opening up a piece of equipment is do a very thoural visual inspection of each component using all senses, sight sound and smell in doing this I did not find anything unusual , I noted everything look quite clean? there was very little dust which suggests light usage.
The Serial #is TW50125 which I gather is an early ,late version , going by appearance and the photos on the TekWiki site? round push button and internal heatsink, I conclude a early late revision and one piece main board, as opposed to the schematic on Tekwiki that has a seperate fuse board.
?John I am prepared to proceed With Troubleshooting in this manner if your willing to see me through untill I get it working, If? I can streach it out at my own pace, and with the understanding that 1 I am handicapped ,working one handed? from a stroke and my short term memory took a hit with a burst anurism, so as to say I work slow and my short-term memory is falty. I haveCML Leukemia but after 8years of Gleevec a truly miracle drug, I'm happy to report my Leukemia has disappeared , undetectable , maybe just to small to detect or just hiding , but at least for the last 3 or 4years undetectable!
I am able to walk and drive , pretty much independent. So doing exceptionally well considering what I been through, I owe it to my hobby in electronics and amateur radio and my Wife Esther a Filipina I meet and married after my first stroke due to an elergic reaction to Cartizem a family of blood pressure medication, just one pill one time nearly killed me! N9OOQ is my call sign.
I usually dont? work on my hobby when Esther is off work, she will be off the next 8days due to my stepson immigrating to the U.S. From the Philippines, so we have a lot of activity planned for him , Mark is 35 ,Esther hasn't seen him in the Flesh for nearly 20 years,
So I will be busy for about the next week or so, I will be reading the mail though, and may even get some brief time troubleshooting, I was trying to get done before Marks home comming!
I have the Job of Chauffeuring everyone around and teaching Mark 35 to drive, so yeah I up for Challenges!Should make a good learning experience for most!
Thanks John and everyone for your understanding and patients!
Best Regards to all!73's?Daven9ooq