EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: Doug Brewster on July 14, 2018, 07:24:06 pm

Title: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 14, 2018, 07:24:06 pm
I'm in the process of dis-assembling a bad HV multiplier out of my SC504 to try and discover what's in it. I'm about 3mm in and have encountered what appears to be a couple of caps and the ground connection. What I'm looking for is info from any previous efforts in this forum to repair these devices in the hope it will save me work; the 3mm progress I've made so far using engineer's burrs in a dremel type drill has cost me an hour of dusty work so far and of course the damage done can make the internals unrecognisable as I found when doing the same job (happily successfully using info from the forum) in my 475, actually a couple of them.

Any ideas where to look? I'm new to this forum and haven't found my way around yet...
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 14, 2018, 09:39:34 pm
I don't see anyone taking these apart and reverse engineering them.
Tek465 HV multiplier replacement https://www.eevblog.com/forum/repair/tektronix-465/msg672083/#msg672083 (https://www.eevblog.com/forum/repair/tektronix-465/msg672083/#msg672083)

All you need to know is how many stages, and capacitor value for the HV multiplier, in 152-0634-00 or CMX222.
I've used a heat gun to basically roast epoxy potting compound and soften it enough to pry off with a screwdriver, to read component values.

Most are 4-6 stage, 1nF or 1.4nF 10kV, BY8212 Philips diodes 12kV 5mA.

I would use 2CL74 (14kV 5mA) to 2CL77 (20kV 5mA) fast-recovery HV rectifier diodes (http://www.e-edi.com/pdf/diodes/2CL69-77.PDF) and 2,200pF-10,000pF caps.

There's some x-ray pics, (http://pp5ms.com/tek_hv/5.jpg) (URL ending in pic #1-6 of link) of a Tek 465 multiplier insides.
The HV connector is the valuable part to salvage.

edit: fixed url
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 14, 2018, 10:03:52 pm
Thanks floobydust for the response. I  think it's a triple multiplier based on the SM info of 3.3KV pk input and 10KV (undefined) anode voltage. Trouble is the housing is about 1 cubic inch in size and it's going to be pretty crowded in there to get the parts in. I haven't tried the heat gun approach, maybe I'll give it a shot...
Title: Re: Tektronix SC504 HV multiplier
Post by: chris_leyson on July 14, 2018, 10:26:11 pm
U1590 152-0634-00 VOLTAGE MULTR:HV MULTR, 6.7kV IN, 10kV OUT. Description in the service manual reads,
"The accelerating potential is supplied by voltage tripler U1590, having an input voltage of approximately 3.3 kV peak."

So the "6.7 kV IN" in the part description is pk-pk voltage. Same multiplier is also used in the SC502.
Title: Re: Tektronix SC504 HV multiplier
Post by: David Hess on July 14, 2018, 10:46:57 pm
Annoyingly depending on the documentation, Tektronix might refer to the same high voltage multiplier as 1.5x or 3.0x.
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 15, 2018, 07:20:09 am
So the "6.7 kV IN" in the part description is pk-pk voltage. Same multiplier is also used in the SC502.

Thanks for the responses. I've measured the input side at 1400V (unloaded) on my rms reading fluke which gets me nearly 4KV peak. My version of the SM doesn't make reference to 6.7KV. This uncertainty about the input voltage is what's making me be careful in the disassembly so that I can determine the number of caps and diodes present....
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 20, 2018, 07:18:33 pm
Been trying to post pics of progress; can't make it work and can't find any help on the topic. Somebody point me the in the right direction?
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 21, 2018, 02:45:49 am
Did you mean posting pics is not working for you? I use" Attachments and other options".  Some people link to image hosting sites.

Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 21, 2018, 08:03:31 am
It's "Attachments and other options" that I can'get to work. The image number appears in the "Choose a file" box when I select a pic but nothing else happens..
Title: Re: Tektronix SC504 HV multiplier
Post by: Gyro on July 21, 2018, 09:04:23 am
Are you paying attention to the size limits? 1MB per image. Max 2MB per post. Try resizing.

P.S. I've been using 'Resize' since Win98 days. Simple, quick and good quality output, single .exe ... https://resize.en.softonic.com/ (https://resize.en.softonic.com/)
Title: Re: Tektronix SC504 HV multiplier
Post by: tautech on July 21, 2018, 09:12:50 am
Been trying to post pics of progress; can't make it work and can't find any help on the topic. Somebody point me the in the right direction?
From yesterday in another thread:
It's not too hard once you know how.
Any one file can't be larger that 1 Mb.
You're only allowed a total of 2 Mb/post.

Use your photo editor of choice to compress pics to a size relevant to the detail you need to show. 100 KB is usually heaps enough detail.
Add them individually into the 'Attachments" UI below this posting box but take note of the file types allowed.

Then they're displayed as thumbnails that you can copy their URLs and place between in [ img ]image[ /img ] tags available from the Insert Image icon.

Sometimes for a few images it's easier to open dual tabs, editing one with URLs copied from the other.  ;)
Just try to get thumbnails posted for now and then work on embedding them at different points within a post.
Remember you can delete your own post if you make a hash of it and a good way to see the syntax of using pics in a post is to Quote that post and examine the layout.
Looks all foreign at first but you soon get the hang of it.
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 21, 2018, 10:00:16 am
Thanks for the responses on my issue with inserting pictures; the files were way too large but I think it's going to work this time.

After having this HV multiplier x rayed and taking it apart, in the course of which I've essentially destroyed everything in it, I now know this about it:-

It contained three capacitors
Two of the capacitors had a connection to the ground terminal
There was a 1.55 Megohm series resistor (by measurement and colour code) in the output HT lead connection

I still have a little more excavation to do and hopefully may be able to get a measurement of one of the remaining capacitors. I haven't even seen an identifiable diode; they must have been ground up in the dust.

(http://[img][img][img][img][img][img])[/img][/img][/img][/img][/img][/img]



Title: Re: Tektronix SC504 HV multiplier
Post by: Gyro on July 21, 2018, 10:59:28 am
Glad Resize helped.

If you want to embed the images in-line with text (I noticed your failed '/img's') then you have to click to expand the thumbnail, right-click on it and 'Copy Image Location', then edit your post, inserting the copied image location between the img and /img. (I've omitted the square brackets for obvious reasons)

To be honest, most of the time, it's just not worth the hassle of inserting the full size images in-line. People can just go down to the bottom and click to expand your thumbnails (which still sit there regardless).


P.S. Nice 'teardown', at least it's yielded most of the information that you need.  :)
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 21, 2018, 05:05:32 pm
A career in Archaeology looks much easier  ;) Glass-reinforced potting compound?! Take it to a dentist for x-rays.

If two capacitors are connected to GND, then it's not a Cockcroft-Walton configuration. There, an odd number of stages (i.e. 3) has high ripple.

It might be this second configuration, works very well but higher voltage-rated parts are needed.

I'm just guessing. Old Tek was very smart, masters of the art and always a learning experience to dig into.
Title: Re: Tektronix SC504 HV multiplier
Post by: james_s on July 21, 2018, 05:12:48 pm
I've had good luck de-potting things with the liberal application of heat from a hot air gun while carefully scraping away the epoxy while it's soft. Xrays also work well and I can usually do most of the reverse engineering without even cutting into the thing.

Something to remember with HV multipliers if they are driving a CRT is that the CRT itself often forms the final capacitor. So for example the doubler used in some of the B&W vector arcade monitors contains only one capacitor and two diodes.
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 21, 2018, 06:46:59 pm
A career in Archaeology looks much easier  ;) Glass-reinforced potting compound?! Take it to a dentist for x-rays.

If two capacitors are connected to GND, then it's not a Cockcraft-Walton configuration. There, an odd number of stages (i.e. 3) has high ripple.

It might be this second configuration, works very well but higher voltage-rated parts are needed.

I'm just guessing. Old Tek was very smart, masters of the art and always a learning experience to dig into.

Re the Cockroft Walton observation, yes, it just doesn't fit any CW configuration I can find. The second schematic you've posted fits exactly the - admittedly limited - facts that I have. Does that configuration have a name? Where can I find some more info about it?
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 22, 2018, 12:39:55 am
I don't see a name for the other multiplier configurations- this is the third I've seen, from a Korean Hung Change scope.

I wonder how much room you have, as 10kV-20kV disc caps are thick 8mm-12mm
I find a 2,200pF part is about 2,000pF out of the box, which further drops to 1/2 that at rated voltage depending on dielectric.
So it's good to voltage-derate the capacitors as much as practical.
Vishay 615R Series 10kV 15kV caps (http://www.vishay.com/ppg?23119)
Digikey stocks nothing but doorknob caps, but Mouser has some, edit: ouch $7 each
Title: Re: Tektronix SC504 HV multiplier
Post by: james_s on July 22, 2018, 12:41:29 am
That looks like a Cockroft-Walton multiplier to me, there are several different ways of drawing them and it can look weird if you're not used to the style.

I've bought HV capacitors from Chinese ebay sellers that worked fine. Diodes too.
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 22, 2018, 01:02:09 am
Cockcroft-Walton has only one cap to the AC input, the other two have both a cap and diode to the AC input, and only the SC-504 multiplier has two capacitors connected to ground. Each looks different to me and performs differently in Spice.

You can figure the voltages each part will see Vpk, 2*Vpk, 3*vPk to save space and money. I'm lazy and just put in overrated parts, especially if encapsulating.

The eBay/Aliexpress 2CL7x diodes I am not sure about. I was going to measure their real breakdown voltage, as their forward voltage is a lot lower than datasheets.
edi HV diodes (http://www.e-edi.com/pdf/diodes/2CL69-77.PDF) spec. 2CL77 20kV Vf=62.5V, 2CL74 14kV Vf=42.5V
I measure Vf=28V on the Aliexpress 2CL77's I bought cheap, so it's a small stack and I thought around 1kV/diode was a ballpark number.
Not sure if the parts are bogus or not.
Title: Re: Tektronix SC504 HV multiplier
Post by: james_s on July 22, 2018, 04:28:07 am
Isn't the difference just that it's flipped around so that what would normally go to the input voltage is going to ground and vice versa? Since it's AC this shouldn't matter.

https://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator#/media/File:Cockcroft_Walton_voltage_multiplier_circuit.svg
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 22, 2018, 07:57:36 am
Isn't the difference just that it's flipped around so that what would normally go to the input voltage is going to ground and vice versa? Since it's AC this shouldn't matter.

https://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator#/media/File:Cockcroft_Walton_voltage_multiplier_circuit.svg

In this CW example there's only ever one leg of a single cap to ground...

Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 22, 2018, 03:16:17 pm
I've put together the second of the two possible circuits presented by floobydust in his post #13 above. It does seem to work well as a tripler, perhaps too well, as it's producing just over 50V for 16V pk in. I'm going to call that measurement error. The numbers are actual output 26.9v + 23.8 volts total diode volt drop (8.26 D1. 7.89 D2 and 7.61 D3). This at 32V pkpk in at 50KHz sine. In the pics the left hand meter is rms reading and the scope is set at 5V/div. To answer an observation above about available space I've included a couple of pics to show the scale of things. One pic includes a AA drycell and another shows this multiplier next to one (homemade but the same size) for a 475.
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 22, 2018, 03:49:22 pm
I should have said in the previous post that the diodes are T73 (12KV I think) and the caps are 2200pF 10KV..
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 22, 2018, 06:08:40 pm
Well, the pressure's on now. A few minutes after my last post the scope in the images died. F3488 blown; 24V supply to the HT oscillator etc.. Put another fuse in and it ran for a few minutes and blew again. I sure hope that the circuit I'm playing with is going to work at high voltage.
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 29, 2018, 01:50:09 pm
Excavations done but with some damage to the case as shown in the pictures. It's difficult to work in these multipliers because of the size. The hole that I punched in the case was repaired simply by using some jewellers/watchmakers protective tape to hold the compound in the case during filling and baking.

This multiplier has gone into the scope that failed as mentioned in my previous post in this thread.

The scope is running very nicely with a clean, sharp trace. I've noticed that the trace is taking about 5 secs to appear from power on compared to 2-3 seconds for my other two SC504s. I've used all 10KV caps (because that's what I had) and the last cap is at full output voltage minus diode drops so we'll see how long it lasts. I'm not too concerned if it fails because the modern potting compound I've used is a lot easier to dig out again. Don't ask how I know.
Title: Re: Tektronix SC504 HV multiplier
Post by: bd139 on July 29, 2018, 01:56:42 pm
Nice job  :-+
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 29, 2018, 04:20:10 pm
That's good news, there's not much room in the box, even for disc caps from the '70s.
What's the second resistor/part values, so I can update and post a schematic- unless you have a sketch. I have 1.5 Meg in series with the output.
You used a two-part epoxy?
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 29, 2018, 04:32:59 pm
That's good news, there's not much room in the box, even for disc caps from the '70s.
What's the second resistor/part values, so I can update and post a schematic- unless you have a sketch. I have 1.5 Meg in series with the output.
You used a two-part epoxy?

I had to use 2 resistors simply because I didn't have a 1.5Mohm. They're 1Meg plus 470K. The two part potting compound is made by Robnor; I got the 50 gram pack which would have done three of these multipliers. Dielectric strength is 14.2KV/mm.

I now have another multiplier to do so I'll buy in parts more suitable for the application and I've also ordered some more burrs. Mine are all burned out...

Many thanks for the circuit by the way...
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 29, 2018, 04:39:44 pm
I should have said in the post above that I've used 10KV 2200pF caps and 12KV (T73) diodes.
Title: Re: Tektronix SC504 HV multiplier
Post by: bd139 on July 29, 2018, 04:41:44 pm
Out of interest, where did you source the diodes? I'm doing an HT refurb on a Telequipment D83 at the moment and the current diodes are getting a bit risky to move as they are crumbling.
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 29, 2018, 05:05:14 pm
Out of interest, where did you source the diodes? I'm doing an HT refurb on a Telequipment D83 at the moment and the current diodes are getting a bit risky to move as they are crumbling.

I "think" I got them out of ebay Germany. I bought and acquired a number of these diodes from about 3 or maybe 4 sources and don't keep good stock control so I don't actually know where I got them. Of course my pc crashed earlier this year and I lost all the emails dealing with the transactions.
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 29, 2018, 05:14:49 pm
Please review schematic for errors, posted for anyone else repairing Tektronix 152-0634-00 or CMX222 HV multiplier.

HV rectifiers, be careful because most are sized to be under encapsulation, for their PIV rating. Only a few are sized for air.
The 10mm-body parts arc over (in air) around 17kV, and 20mm-body are what you would use in air, like 2CL77 (http://www.e-edi.com/pdf/diodes/2CL69-77.PDF) at 20kV.
The ones on eBay/Ali are so low priced, I have been using them with no troubles, although Vf is lower than most (smaller stack).
Inverter microwave oven rectifier diodes i.e. Sanken UX-F5B (http://www.semicon.sanken-ele.co.jp/ctrl/en/product/detail/UX-F5B/) are huge, for 350mA at 10kV.

edit: forgot part number
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on July 29, 2018, 05:37:33 pm
That's great floobydust. I'd suggest a 15KV rating for C3 but physical size may be an issue.
Title: Re: Tektronix SC504 HV multiplier
Post by: floobydust on July 29, 2018, 05:46:26 pm
2,200pF 15kV (http://www.maxcapacitor.com/en/product_details.aspx?id=148) is 1mm thicker and 2-3mm larger diameter, depending on dielectric Y5T or Y5U but these no-name caps who knows what is used in them.
Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on August 15, 2018, 04:25:54 pm
Made a couple more of these HV multipliers, one for the failure that occurred earlier in this thread and a spare for my third SC504 which still operates on it's original multiplier. This time I've used a 6.6KV (2200pF) at position C1 and a 15KV (2200pF CERA-MITE Z5U) at C3, leaving C2 at 10KV as before. It was only possible to get a 15KV into the box by reducing the size of C1.

I almost destroyed the box of one of these; got too close to the side with the burr in getting the output HT lead out and thinned the wall so much that it collapsed in my hands. Had to use some temporary walls clamped to the outside so that the potting compound could be poured in and baked and removed them later. One of the walls that was destroyed was that which contained the input and ground terminations. Fortunately it was possible to simply rotate the box 180 degrees, drill some new holes in the sound end of the box for the termination ferrules and another hole in the base for the new position of the output HT lead. All of this meant that I was then installing the components from the opposite side to that which I'd used previously so had to relearn the process; putting these together in such a confined space really is a chinese puzzle..

Anyhow, they're both running fine. Here's a few pics..


Title: Re: Tektronix SC504 HV multiplier
Post by: Doug Brewster on June 11, 2019, 08:10:49 pm
An update. Spent last week in the English Lake District in a caravan and took with me some "toys" as my wife describes them, to avoid going nuts watching TV in the evenings. One of the toys was the scope containing the first HV multiplier I refurbished which contained the marginally rated 10KV caps identified in post #24 of this thread.

The weather was extremely wet and I was running the scope in a TM515 power frame sitting on it's  backside, on a plastic sheet but nevertheless wet ground. It apparently sucked up wet air from the damp ground via the cooling fan and the HV started to arc; I could hear it quite clearly and the trace brightness zoomed up and down several times before I got to the off button. It's been dried out for a few days and is working fine.

Lesson learned but it seems to me to say a lot about modern caps...