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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

Hi, my 576:

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

On Tue, Aug 27, 2019 at 11:59 PM, <randolphbeebe@...> wrote:

Albert,

I re-read your post about the V609 voltage reference tube and it occurred to
me that I could not test the 5651 tube with my tube tester so I just put it
back in. However, I had another one my stash and I just replaced it. Now all
the voltages came inline perfectly. I now have a perfectly working 585A!
Next I will attempt to calibrate it.

Cheers,

Randy

Hi Randy,

Well, that was an easy repair after all!
I started reading reading your measurements results before I saw this last message. This last message is in a new thread for some reason. My conclusion was indeed that the LV supply was still in regulation and the voltage across V609 was the culprit, way too high. The ratios 182/150 and 107.4/85 are almost the same. Though the grids of V624 differed more than I thought, the anode voltage (about 0 V) was clearly not near the end of the possible range. [You probably did not measure differentially between the grids, and even a 10 Mohm DMM input has some influence when you need the difference between large DC values.]
BTW You also reported pin 4 of V634, which is the 6.3 V AC heater supply. I don't know what your DMM (-2.4 V ?) does with this, but just ignore it.

I am not sure if this is related but I seem to get a short between Ground and the positive terminals of
C790-791-792 ( All have been replaced now) of the regulated heater supply (Upper Left portion of the
LV Power Supply Schematic). It appears to be isolated between the Emitter of Q797 and Diode 793
and Diode 792 somewhere. Is this normal?

I think you were mislead here by resistance measurements. The "+20 V" is also loaded by the K600 coil. It's clear that the "+20 V" is present, otherwise the time delay relay would not switch in. You might check the regulated +12.6 V DC output if you still don't trust it.

I am much more reluctant to replace components!

Albert

To close this:

(a) Thanks Dennis
(b) the heatshrink plus some other support for the solder joint is absolutely essential for the soldered-pin-only solution, otherwise the joint is just to weak and will break within days, as I confidently expect this one to by the time Dennis' lead arrives.

EJP

I plan to replace some electrolytic and tantalum capacitors on the main board of the 577.

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

I notice 2 tiny electrolytic capacitors, C218 C215, I didn't know they made these so small, I will replace them with these tantalum capacitors ()

And finally C268 and C265, these look like a tantalum capacitors but they are red on the tip, purple in the middle, and yellow on the bottom, based on my serial number 092694 D1 storage I believe these should be 0.47uF 35V, I will be replacing these with tantalum capacitors ()

Any comments or advise on these capacitor selections?

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

Albert,

I re-read your post about the V609 voltage reference tube and it occurred to me that I could not test the 5651 tube with my tube tester so I just put it back in. However, I had another one my stash and I just replaced it. Now all the voltages came inline perfectly. I now have a perfectly working 585A! Next I will attempt to calibrate it.

Cheers,

Randy

Albert,

I am not sure if this is related but I seem to get a short between Ground and the positive terminals of C790-791-792 ( All have been replaced now) of the regulated heater supply (Upper Left portion of the LV Power Supply Schematic). It appears to be isolated between the Emitter of Q797 and Diode 793 and Diode 792 somewhere. Is this normal?

Thanks

Albert,

I checked the voltages and here is what I measured after a 10 minute warm up;

Tube Pin Voltage

V609 7 -107.4

V624 6 +1.5
7 -107.6
2 -104.0

V634 6 -38.0
7 and 2 -87.0
1 -87.1
4 -2.4

V627 9 +69.0
V637 same
V647 same


As you mentioned in you previous reply I found that pins 6 and 7 of V624 vary widely. I changed that 12AX7 with no change.

Thanks Again,

Randy

Hi John, Yes Thanks this is the kind of help I need , Yes did check the secondaries voltage wise but not under load,? ?I'm rather busy lately and I have to confess I have not done the math to calculate the resistance I need for a 2amp load.?I dought I have the resistors in the wattage I need,? I do have a 2ohm 100 watt resistor handy. I have a bunch of others on order from china expect them in about a week.?
I'm expecting my stepson? ?to immigrate to the U.S. From the Philippines Thursday the 28th . so lots to prepare and hard to predict how much time I will have in the future.??Hopefully next week I will have more time? but working one handed due to strokes , so it will have to be spread out over days if not weeks!
But yes this is the correct methods? for troubleshooting taking nothing for granted.
?Yes I did print out the schematic but did not page them togeather as I should have.
I do see the +and - 15volts comming of the references on both sides , there are 4 fullwave bridge rectifiers I have checked both variable sides I recapped all filters , Im forced to kind of short cut? testing everything, due to time constraints and lack of a variable load.
I do very much appreciate your methods though and will go back ,when time permits? and report the results so others can learn? from this , This is what this group is for.?
Many Thanks John!Daven9ooq

Checking these voltages now. Thanks Albert

Hi Steve , Can you tell me more, were the banana plugs over tightened? , or its it a manufacturer defect, have you repaired it ,if so how, please tell us more!?
Many ThanksDaven9ooq

Thanks for the comment I Think we established the PS280 was not made by Tektronix although it carries their? name, and was out sourced toGoodwill industries.
I really could use some help troubleshooting this supply? I did a full recap on the 2 -0-30volt supplies, they do go down to 0 volts and in fact will go negative if you adjust it so, At present I am getting about 15 volts max. on the main side and little to nothing on the slave side, waiting for load resistors to come, maybe about a week more,? There is a Theroy of operation in the manual one Tekwiki although the manual is for a different? version, all versions seem to use the same circuitry , just different construction and appearance.
I'm quite busy at the moment and in the near future, I really could use to get this off my bench quick but could use help with Ideas on what to check and how to proceed.
Many thanks in advance!
Daven9ooq.

Dave thanks for the information on the catalogs. I was not aware of the wifi site. I will have a look.

Thanks again

Richard W4MCD