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Late 1970s SMPS Design Query

The caps are through-hole components. Their solder joints are visible in the images of the bottom of the board.

If you don't have a desoldering pump, then heat one lead at a time from the solder side, and pull gently from the component side. It may shift only a little, at each attempt. Alter the leads and repeat at each attempt, as the leads gradually withdraw. Add solder to maintain ease of heat transfer to the heated lead.

These caps are not tolerant to overtemperature or physical mishandling. They were manufactured to a 2% tolerance of capacitance and should measure no more than 3% tolerance at end of service life.

Please complete the troubleshooting steps resulting from visual inspection.

You still haven't identified the types of diode used to replace the original BY200-1000 parts previously, identified in visual inspection.

RL

Reply to
legg
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On a sunny day (Wed, 27 Jan 2016 14:58:24 -0000 (UTC)) it happened Cursitor Doom wrote in :

Driver base emitter? is IS OK, but note it is ON (the positive side) for much too long!!!

Collector emitter driver? OK

BU208 base emitter?

It is posible your probe is picking up stray signals from the nearby HV pulses. You should use 1:1 probe on BE (cannot be moe than 10V eklse BU208 is dead Vbe) Try showing 1 or 2 periods, this mess is hard to read. Cannot say what the duty cycle is there from this picture.

Reply to
Jan Panteltje

Thanks, Jan. I've learned a lot about resonant converters in this thread, but it's still my first hands-on exposure to them and whilst I may now know about 1% of what there is to know, the other 99 isn't going to come overnight. So like I say, I'm going to tuck it away with a print-out of everyone's comments and suggestions and attack it again in 12 months from now. I'm sure it'll seem a lot less daunting by then!

Reply to
Cursitor Doom

Noted and filed. Thank you, legg. Please don't put any more time into this as I'm mothballing it until such time as I acquire more knowledge of this somewhat unusual topology. It's beyond my current level of experience so I'm going to read up on these beasts before attacking it again. BTW, that 20 ohm resistor still very quickly gets way too hot even when the load is reconnected and on so something is still amiss here. But enough already! thanks again.

Reply to
Cursitor Doom

On a sunny day (Wed, 27 Jan 2016 16:04:29 -0000 (UTC)) it happened Cursitor Doom wrote in :

mm defeat? never give up, even ... There is nothing secret about 'resonance', just a tuned output stage that get kicked, like a pendulum that you tap to keep it swinging, at the right moment, And that is why the frequency and caps have to be exact.

Its only a scope supply. No magic.

Reply to
Jan Panteltje

Not so much exact, as the correct distance off resonance, in this topology, so that the fixed-frequency variable PWM can push it. The transformer never sees full resonance, as this would be incompatible with the control method.

RL

Reply to
legg

The resistor will also heat due into a faulty output, but at least you should have something to troubleshoot, if this is the case.

I sometims find it useful to take a break.

Reading has its place, but if you gloss over what you read in the same way you have glossed over these posts, you won't fix this thing.

Manual soldering, measurement and procedural/recording skills will not be easily obtained/improved by collecting/reading articles or by fiddling with the computer.

RL

Reply to
legg

No kidding? ;) But seriously, I'd have a fighting chance if the damn thing didn't start to burn up before I can hardly get a meter on it.

Also: I have ZERO information on this scope. Someone's previously repaired this board at least once. Someone else again may have 'had a go' later and done god knows what to it, twiddling this, twiddling that, you know how it can be with some screwdriver jockies. We're assuming all the pots are in the right place; they may well not be.

It's also been modded either by the factory or some service technician and differs from the published schematic in places.

I'm not giving up; I'm merely postponing further investigation until my level of experience is closer to that required to deal with this. In the mean time I've got a pile of other old scopes to get that experience with!

black magic!

Reply to
Cursitor Doom

So do I and that's what I'm going to do as I'm getting impatient and frustrated and will end up toasting it if I don't leave off now. Thanks again for your assistance.

Reply to
Cursitor Doom

On a sunny day (Wed, 27 Jan 2016 12:06:12 -0500) it happened legg wrote in :

That depends, in a class C output the 'on' time can be any fraction of a half period I'd think. I agree that the 'on' time here is likely much less, or should be, but maybe is not (what it should be).

Same as short tick with a feather versus a long push with the hand, for the pendulem case.

Reply to
Jan Panteltje

On a sunny day (Wed, 27 Jan 2016 17:52:29 -0000 (UTC)) it happened Cursitor Doom wrote in :

Discrimination!

I was thinking maybe if you had a variac and could slowly power things up, but you would have to power the oscillator separately.

Reply to
Jan Panteltje

I do have a variac and have been using it. Now I plan to use it on something else.

Reply to
Cursitor Doom

On a sunny day (Wed, 27 Jan 2016 18:51:10 -0000 (UTC)) it happened Cursitor Doom wrote in :

Light bulb?

Reply to
Jan Panteltje

20 minutes is usually enough.

RL

Reply to
legg

12 months sounds better. Another important point is that I have at least 3 and possibly 4 other Philips scopes of around the same vintage. If by chance one of them should use the same or similar psu board then (provided it's in working order) I will be able to take useful measurments from that for comparison purposes with the faulty unit & maybe swap parts over and whatnot. It's got to be worth a shot at least!
Reply to
Cursitor Doom

I found your projects site very interesting. If you still maintain it, a link would be nice. I mess around with similar stuff.

Reply to
Cursitor Doom

Like I mentioned earler maybe it doesn't like no load. It's not a modular or bench power supply. It's an old switcher. Lots of them act real stupid with no load present.

At least connect a light bulb or something to the 5, 6 or 12 volt outputs.

Reply to
Cydrome Leader

I was a LeCroy booth at a trade show. nobody there, even the guy with LeCroy business cards could figure out how to display the square wave test signal off the front bezel.

Even setting AC or DC coupling involved screwing around in menus for a while.

It appeared to be a completely worthless piece of test equipment.

Reply to
Cydrome Leader

We have a 4-channel 6 GHz, 40 Gs/s Le Croy scope and I can't get it to do anything. But some people here have learned how to drive it, and it can do really impressive things.

It can make an eye diagram from a PCI express signal with no trigger. It takes a really long record and applies a software PLL to fake the data clock; that's impressive.

We just bought some fet probes for that scope off ebay, for about $2K total. The differential probe alone is $7K new.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

It won't run right loaded (with the correct load) or unloaded. You must have missed the posts during which that was stated. Thanks anyway.

Reply to
Cursitor Doom

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