Ortec 556 Schematic

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aka47
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Ortec 556 Schematic

Post by aka47 »

Hi Guys,

I have recently aquired the use of a (in need of repair) Ortec 556 High Voltage Power Supply to use as a bias supply for some PMT detectors I am workign on.

The 556 is not regulating and makes a thunking sound. There was another one that I don't have but this one was making a thunking sound and regulating poorly.

From my experiencing servicing and repairing other Electronic kit this looks a little like it could be a stock fault.

Just before diving in an plodding through it the long way, (In to out). I was wondering if anyone had a schematic for the 556 that they could let me have a look at, or maybe even knew if it was a stock fault and what it was.

At the moment I am quesing that it may be the sensing divider, but without having taken the back off yet this is realy a guess.

TIA

Andy Kirby
George Dowell
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Re: Ortec 556 Schematic

Post by George Dowell »

aka47
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Re: Ortec 556 Schematic

Post by aka47 »

George

You are truly a star. Many thanks.

That is perfect.

When I have worked out what the fault/s were I will post back in case it helps anyone else.

Cheers

Andy Kirby
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Richard Hull
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Re: Ortec 556 Schematic

Post by Richard Hull »

Be mindful that a huge number of issues with all NIM modules are the low voltage tantalum couping, bypass and filter capacitors which fail enmass with age and use.

I have an extender that lets me feel the tantalums while operating. They must never be warm to the touch or they are bad or failing. Sometimes, they just simply blow up and are easily seen.

As this is a high voltage supply I probably would resist poking around with my hands while it is on. Let it run a bit and then turn it off and feel the tantalums.

I now have a special instrument that checks electrolytics in circuit without even running the item. It is fabulous in repairing switch mode supplies that typically brutalize such caps.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
George Dowell
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Re: Ortec 556 Schematic

Post by George Dowell »

Correct on the wet slug tantalum capacitors self destructing. In the good(?) old days when freeze spray was cheap, we could douse the board 1/4 at a time, turn it on and watch the frost dissapear from defective (heating up) components.

Nowadays a cheap liquid crystal sheet does about the same thing, although not as spectacular to watch.

George Dowell
aka47
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Re: Ortec 556 Schematic

Post by aka47 »

The original fuseholder was missing the fuse part so replaced the fuse holder and ran it up.

The ± 12v rails look to be functional (more like ± 11.6) and are
powering stuff like the panel meter, LED Ok.

The PSU just keeps ramping up volts wise even though I have it set up
for 200V. Decided to switch it off at 2.0Kv as it was still going.

So I don't want to leav it switched on for too long.

The HV does'nt seem to bleed off too quickly either when I powered it off. So I plan to be v cautious.

Next step is to probe the feedback chain.

Will halt on this one till my HV Probe arrives, should have been here a
couple of days ago.

Rapid Electronics seem to have missplaced my shipment. Don't fancy probing the wrong side of an OC component in the feedback chain with my multimeter. Shocking.

Have left the PSU with a 10M bleed across the output to discharge it as it is turned off and will regroup later when the probe arrives.

All in all the HV generator side seems to be functional it looks to be the sensing and or regulator bit that is pear shaped. The HV section is mostly in it's own screened off subcompartment.

Once I have verified that the feedback chain looks sensible and no HV is creaping to where I want to do LV work we should be go to work through the regulator/control signal generating bits.

Hmm yes I take the point re duff capacitors and heating I will try that, well reminded.
aka47
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Re: Ortec 556 Schematic

Post by aka47 »

BTW George, I think QSL net has gone off air. I just returned for a look at some of your awesome collection and got "Error 404 - Page Not Found"

Cheers

Andy Kirby (G1HOU)
aka47
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Re: Ortec 556 Schematic

Post by aka47 »

OK

My high voltage probe has arrived and some lurverly thermochromic film so I can see hot spots. WIthout getting my fingers in.

After waiting for there to be someone else in the house just in case.

First check was to run up the PSU, with the side off, thermochromic film over the Low tension part and High Voltage probe hooked up to the output.

Turning it on the voltage on the front panel meter climed quickly to the set voltage and just kept going. Same as before.

The voltage on the output though rose to the set point and stabilised off nicely. So it looks like either the panel meter or the feedback chain to the panel meter that is goosed.

The thermochromic film onlly appeared to show warmth over the power transistors that were there so this is promising. No obvious warm bits over capacitors. Although I did not leave it on for that long.

I tried a couple more settings and the output ran up to them and stabilised off nicely.

The panel meter on each trial came back on with the last voltage it read. But the High voltage probe was showing that the 10M bleed I put across the output was running the voltage down quite well.

It is looking more liekly that there is a break in the feedback chain somewhere and a capaitor is just charging up. This being what the panel meter is reading.

Next stop a read of the schematics and a run over the panel meter feeds.
John Futter
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Re: Ortec 556 Schematic

Post by John Futter »

Andy
there is an electro cap in the feedback chain that tends to go leaky which causes the output volts to overshoot also check the pot to make sure it is all there
aka47
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Re: Ortec 556 Schematic

Post by aka47 »

Ok finaly got some time and sorted this one.

All working and calibrated.

The problem in the end was that the panel meter had no ground connection. I guess it can never have worked this way. The meter clibration pot was so out I guess it was never correctly calibrated either.

Piccy shows the com connection unsoldered.

I dont' fancy ortecs QC much....

All done now.

They do make a funny ticking or very quiet thudding noise. The rate is directly proportional to the load and output voltage so I am guessing it is pulsing of the step up transformer. My high voltage probe certainly seems to show the voltage as being stable.

As I have another two to fix I am seriously considering making up a potted High Voltage divider that I can use to put the low voltage side into my scope so as to check ripple etc. SHV input BNC output.
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Joe Gayo
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Re: Ortec 556 Schematic

Post by Joe Gayo »

The previous link is dead (as already mentioned).

I would be most grateful for a schematic of the 556 Ortec.
VladProc
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Re: Ortec 556 Schematic

Post by VladProc »

Not sure how to upload files to the File sharing section, so I uploaded 556 schematic to Gofile: https://gofile.io/d/NfCZw9


Edit by Joe Gayo - File Attached (Thank you!)
Ortec_556 Schematic.pdf
(407 KiB) Downloaded 234 times
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Dennis P Brown
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Re: Ortec 556 Schematic

Post by Dennis P Brown »

Vlad, thanks for that post! Hope you decide to become a regular.
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