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Old 1st November 2005, 01:56 PM   #1
Giaime is offline Giaime  Italy
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Question My scope doesn't work - need help!

Hello to everyone!

I just acquired an old Scopex 4D10B oscilloscope for free, just to start doing some electronics diy works, like tube amps and preamps etc etc. It hasn't the cable that you use to make measurements (don't know the english word, sorry), but when you turn it on and wait for warmup, it doesn't show an horizontal flat line, like other scopes I've used, but a single dot, that sometimes extend itself into a small line, sometimes it moves randomly and slowly to the right...
No matter where i turn the knobs, I still have a single dot. I've followed the turn-on procedure in the manual, but nothing...

I've got the service manual with schematics and adjustment procedures, but I haven't found any info about it except for this eBay auction http://cgi.ebay.co.uk/SCOPEX-4D-10A-...QQcmdZViewItem
that shows a very similar one (mine is black).
I've never worked on scopes, but I've already worked on tube and ss amps, and dealt with high voltages. Can someone help me?
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Old 1st November 2005, 02:04 PM   #2
Netlist is offline Netlist  Belgium
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'Probe' is the name of the cable.

Re. your dot: I suspect a bad soldering in the horizontal amplifier stage. Or your time base could be in the xy position, but then the spot wouldn't move along the screen.

/Hugo
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Old 1st November 2005, 02:09 PM   #3
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Default Re: My scope doesn't work - need help!

Quote:
Originally posted by Giaime
SCOPEX-4D-10A-DUAL-TRACE-OSCILLOSCOPE_
50 pounds ?

Quote:
hoaw..hoooaaaoow..hooooaaaaw..haaaaw…hoaaaaaaawww.
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Old 1st November 2005, 02:27 PM   #4
Giaime is offline Giaime  Italy
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Default Re: Re: My scope doesn't work - need help!

Quote:
Originally posted by Netlist
'Probe' is the name of the cable.

Re. your dot: I suspect a bad soldering in the horizontal amplifier stage. Or your time base could be in the xy position, but then the spot wouldn't move along the screen.

/Hugo
Thanks Hugo, I just forgot the word "probe"
So I'll open it and check for bad joints, since the other day i turned it on and it showed some kind of horizontal line

Quote:
Originally posted by jacco vermeulen

50 pounds ?
Sorry, what do you mean?
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Old 2nd November 2005, 05:26 PM   #5
Giaime is offline Giaime  Italy
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HELP ME!!!

I've resoldered everything in the 'scope, but I can't get the horizontal line, only a single dot and strange behaviour.

I'll try to explain...

Every control does the supposed action to the dot, BUT the horizontal (position?) control only moves the dot very little, and when I turn the TIME/CM rotary switch, the dot moves to random positions on the screen, and sometimes creates a small horizontal line on the right of itself, and many times the line is changing, making itself smaller or longer... This 5 minutes ago: now I turn the aforementioned knob but now the dot doesn't move (except for the "x-y" position).

What can cause this? All other controls are in the 12 o'clock position, all pushbuttons off, nothing attacched to the various inputs (no probes).

Please! I need Help!!!
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Old 2nd November 2005, 05:57 PM   #6
anatech is offline anatech  Canada
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Hi Giaime,
Long time. I'm glad you got a 'scope.

No horizontal sweep. The horizontal amplifier isn't working, or you may have dirty switch contacts. I am not familiar with yours, but some have a switch on the back too.

Always check the power supply voltages first. Once you are sure that's okay, go further.

Can you send the schematic of the horizontal oscillator and amplifier circuits? That will give test points. Also the power supply for the same reason.

-Chris
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Old 2nd November 2005, 06:21 PM   #7
Giaime is offline Giaime  Italy
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Hi Chris! Yes, it's been a long time

I got this scope from a fellow at www.videohifi.com, a hi-fi oriented italian forum: we were talking about scopes and professional DMMs, they said that good entry level ones are going for peanuts, and I asked if someone could give me a scope really for peanuts because I couldn't find one... An experienced tech out there (his site http://www.sistecgps.com/ they make custom gps) sent me a full working professional DMM (Schlumberger Solartron 7050) and this scope FOR FREE! He even refused to accept the s/h money, he said it was for my birthday (22 october now I'm nineteen).

I found a dead capacitor in the 'scope, it is a 1000uF 40V, it is the first PSU filter cap for the +20 supply. It's leaking some strange green substance, even on the pcb other than from it's positive terminal. I guess it's bad in fact it measures dead open.

I think he is the culprit, but I also think that he's the only one, since after that cap there is a fully regulated supply. I will replace it and keep posting...

And no, I can't post a schematics, since it isn't avabile in the Net and I have it on paper, but I don't have access to a scanner right now...

Thanks to all!!!
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Old 2nd November 2005, 07:23 PM   #8
anatech is offline anatech  Canada
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Hi Giaime,
Make sure you get all the stuff cleaned off the board. Then do voltage checks. Beware to stay completely away from the focus / intensity controls. Hold a neon bulb near wires to check for really high voltage. Use insulated pliers & do not touch the wires!

Just may sure you are testing in the low voltage areas. I'd hate to see you blow up your "new" meter.

Congrats on your birthday present!!

You can email a picture of the schematic some time.

-Chris
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Old 2nd November 2005, 07:49 PM   #9
SY is offline SY  United States
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Giame, this is one where you can really fry yourself. If it's not something easy (and I think you looked at the easy stuff), you might want to weigh the 100 euros or so it would cost you for a good, working scope versus the risk to your life. And, secondarily, the risk to your meter.
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Old 2nd November 2005, 08:37 PM   #10
Giaime is offline Giaime  Italy
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You are perfectly right, both of you. I was thinking to have it repaired by a local TV tech, a friend of mine. He works on TV sets, so CRTs and HV are his everyday job So I can also have it perfectly tuned.

Thanks to everyone!
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