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Sorry that should say "and I noticed the 33uF/160V on the 100V PSU output WAS DAMAGED, I REPLACED IT,...."

Good news! I replaced the PSU filter caps, and I noticed the 33uF/160V on the 100V PSU output, and it's all good!

Looking at the base of this capacitor, it was quite obvious that it was the failed one, the black epoxy has come off near one of the legs and when I attempt to measure it's capacitance on my (cheap) multi-meter it reads almost 0nF. In fact, I think the black epoxy had come off under such pressure that it pushed the cap up, and crack the solder joint!

Look at the difference nice new caps have !

Thanks very much for your help, Tom, very much appreciated!

Max

Hi,

I've been working on a 603 XY and began by recapping and testing on
Variac, which cleared up display bloom and a squiggle.

What I have now is:
* a somewhat defocused (2-3mm), very bright spot
* unresponsive intensity control
* focus control has effect but cannot focus spot

All the above seems to indicate a HV issue. I am waiting on a HV probe
so I don't have a measurement yet. But, possibly related:

Was not able to bring the -30V into spec, rails currently measure
+215: about 250
+15: about 17.7
-30: about -36

The -30V adjustment is R878 trimmer but it has no effect on the voltage.

I'm looking at the regulator section schematic, I've checked the VR870
zener and it's nominal ~ 6.2V.

I'm pretty new to repair so I was hoping for a pointer or two to where I
could look at re this initial inability to regulate or trim -30V.

I believe this is the most relevant part of the schematic:
/g/TekScopes/photo/249616/0?p=Created,,,20,2,0,0

--Toby

Hi chipbee40
Yes, I am on 220v
Thanks

Hi chipbee40
Thanks for your concern and suggestion.
For c906 I had replaced by 100uf 450v type. And now I checked out of the circuit the esr meter shows 98uf and 0.34 esr.
Thanks
Saroj

I have two of these:



Now obsolete for my purposes as I have a couple of Leo Bodnar's marvelous <40 ps units. If anyone is interested in them PM me and I'll take photos. I am only keeping them until they find a proper home.

I'm in central Arkansas.

Have Fun!
Reg

Hi Max,

Any progress? Today I used an S-52 on an extender, case removed, and then thought of your problem. I read your first post once more:

The only missing waveform was the TD output.
At this point I removed the original TD assembly welding, at the points indicated in the manual, one 1N3130 instead.
Power on...Still no result.

The 1N3130 is a 50mA/25pF TD, while the original one is 50mA/1.5pF. Hence I think the small cap C65 will not pass enough current from the snap-off diode to fire the TD in a stable way. The bias current would have to be unrealistic close to the firing current.

To my surprise, around + 13V I notice that an output waveform appears, although not synchronized.
I connect the TRIG OUT of the S-52 to the 7B80 and the output of the S-56 to the 7A26 both with 50 ohm termination.
I set the trigger, 2us / div and ... Wow! Perfect! The waveform is absolutely identical to the 14A waveform reported in the manual.

I doubt so. The proper output pulse probably doesn't start nearly immediately after the sweep start (period 8) but earlier, in period 7, so up to 1 us earlier. Simply because the arming bias current in period 7 is already high enough to fire the TD.
In my previous post I wrote:

An increasing supply voltage also has effect on trigger level as if the wiper of R90 is turned towards the
top terminal (base Q90). Then the trigger pulse from the snap-off diode can be insufficient to fire the TD.
This can be compensated by turning the wiper towards C90 Has the wiper good contact all over its whole range?

Here I overlooked the current delivered via R97+R98. That current will increase when you increase the "+15V" level. Are the values of these resistors still in spec (not replaced by smaller values)?
When you say that the pulse disappears, does that mean that the output stays low, or that the output is high over a so long period that you don't consider this as the proper pulse?

Albert

I see a couple of spiders plus some styrofoam.

--Victor

I don't see in your messages where you have checked C906? Usually if 2 bridge rectifiers fail it burns out C906 (Large can), so you get rippled volts going through the power supply causing damage.
I'm guessing you are on 220Vac?

Hello--
The books are sold-- my thanks go to everyone who inquired.

73--

Brad? AA1IP

- David Berlind5:16am #168839
--Somewhere (it has been a long time since I saw it), there's a video showing the cheap construction of the Chinese variacs [sic], the inaccuracy of the dial and the readouts, and the need to implement a fix to the shaft because it was slipping. --Ever since I saw that video, I decided to keep my distance and stick to the American made heavyweights.

Hi David,

LOL! I am so amused by this bashing of Chinese variacs!

It reminds me of the days, long long time ago, when Japanese cars were all "junk", compared to the nice big cars made in the USA, big heavy sedans with voluptuous tails.
In two months my Japanese made Nissan Maxima 1995 will be 26 years old, and ... it's the best car I have ever owned, it runs like new.

Let's see if I can dramatize my Chinese variac a little:

When the Chinese variac I bought from Amazon arrived, I opened that heavy box and tried to remove the variac from inside. All I lifted was the handle, which was loose. Then I grabbed on the red metal case to lift, but only the case came out, the screws that hold the variac inside had gotten lose and fallen off. With that red case came the wires to the outside, and with the pulling, they all broke lose. Finally, I could grab the heavy core but with its weight I broke one of my glued-on nails. The core looked fine, but the winding was full of kinks like the toroidal core had been twisted. The exposed track on the winding was irregular and everything was covered with carbon dust from the finger that rides it. When I tried to plug in the variac, the two prongs of the plug fell off. The power cord was so flimsy that when I tripped over it, it broke in two. One week later I had managed to put all the pieces back together, and when I tried to bring up the voltage I realized that the winding was backwards, so as one moved the dial from zero upwards, the output started at the highest voltage and went down. Maybe in compensation, the needle of the little AC meter tried to move in the opposite direction, into the "negative AC". After 10 minutes the unit started to overheat and smoke. Then I realized that for the core they had rolled up some soft iron from old cans, it was saturating horribly, and the output waveform was not sinusoidal anymore but it was totally distorted. I had plugged into the variac my 547 scope, and that distorted AC supply made its CRT implode. Also when moving the handle, one could see intense sparking inside and a smell of burned material. Still on the first trial, I realized that the plastic handle was somewhat conductive, and as soon as I started moving it I got a terrible shock. I fell to the floor, and the Chinese variac fell on top of me. I am writing this testimonial from my hospital bed.

Ernesto

Hi Leo
I put on the scope without limiter bulb, it took away q9070, cr901and
cr903. Fuse also blown away and ac mains tripped.
I could not see any obvious short circuit
near Q9070.
At the beginning, before we started talking to each other I had checked
the u930 for its operation with external supply across C925. That time I
measured the ramp at pin 5.
The frequency was 56KHZ with 52%duty cycle and the pulse frequency at pin
10 was also 56KHZ with duty cycle of 94%.
Is that a normal situation or the duty Cy le of both the ramp frequency and
pulse should be same.
I could not see any circuit path for that limiter bulb light so bright.
And one thing more, in the circuit diagram +I've rail for inverter
input(Tp950) and circuit ground is always confusing.
Regards
Saroj

On Tue, Jun 30, 2020, 3:29 PM Saroj Pradhan via groups.io <sarojman.Pradhan=
[email protected]> wrote:

Hi Leo
Put on without limiter bulb.
Took away q9070, cr901and cr903.

On Tue, Jun 30, 2020, 12:31 PM satbeginner <castellcorunas@...>
wrote:

Hello Saroj,

the high pitch sound should indicate it is trying to oscillate and turn

on

the FET.
The one you have should be OK too.

The thing is, the inrush current of these switch mode PS is very high, so
it could be the bulb preventing it to switch on properly...

If you don't find any obvious shorts around the FET and other transistor,
I would try it without the bulb...
Connect a voltmeter to the expected 43V and see what happens :-)

Good luck,

Leo

It puts a smile only face reading all these "made in the US of A" comments :-) versus "Made in PRC"

I'm really happy with my Dutch, Philips made, insulated adjustable transformer, which, IMHO also is indestructible :-)

Although Philips stopped making them, the division in 's Hertogenbosch who build them was sold, but till today this division -as a seperate company- still builds them.

A friend once sent me a smallish meter from Aussie land.? When I opened the case there was a humpty great spider in residence.

Fortunately, it was dead. My friend was horrified !!

I'm not sure if he was upset because it was in there, or because it was dead!! ;-)

Now very cautious opening packages from foreign parts ;-)

Dave

Somewhere (it has been a long time since I saw it), there's a video showing the cheap construction of the Chinese variacs [sic], the inaccuracy of the dial and the readouts, and the need to implement a fix to the shaft because it was slipping. Ever since I saw that video, I decided to keep my distance and stick to the American made heavyweights.

Sorry to push the limit Dennis but I had to add an Aussie perspective ... we don't have a problem with critters in our cars. The snakes will get them:



:)

Graham

--
This email has been checked for viruses by Avast antivirus software.

Hi Leo
Put on without limiter bulb.
Took away q9070, cr901and cr903.

Hello Saroj,

the high pitch sound should indicate it is trying to oscillate and turn on the FET.
The one you have should be OK too.

The thing is, the inrush current of these switch mode PS is very high, so it could be the bulb preventing it to switch on properly...

If you don't find any obvious shorts around the FET and other transistor, I would try it without the bulb...
Connect a voltmeter to the expected 43V and see what happens :-)

Good luck,

Leo

Hi
Did you go through my previous message?
There I described some of the activity and results.
I appreciate if you comment on that.
Thanks saroj

Hi,

I think that should be ok.
As far as I can see in the 494 the reference has a bit more room, compared to the 595.
But being in the first stage of the power supply, maybe it's not so critical.

Un saludo, Leo