Toasted SOAR Corporation O-scope

Discussion in 'The Projects Forum' started by Andy S., Oct 8, 2007.

  1. Andy S.

    Thread Starter New Member

    Mar 26, 2007
    9
    0
    First off, my apologies for this being some what lengthy, but I felt that some details were needed.

    anyhow, here goes.....


    OK , I tried to buy an oscilloscope on ebay a short while ago. Won the auction, package arrived. Problem, the way the thing was packed, the bottom of the casing (metal) was pushed up just enough to touch some of the circuitry. I didn't realize that until......Powered it up, Poof!! Sniff, sniff? smoke was released!!

    Ok, the seller was great. Gave me a refund but said to do with it what I wanted to do. I had checked out getting it fixed by a local repair place, but they wanted a minimum $75.00 and that was just to start, no guarantees.

    So I put it out with the trash. Well, there's this guy that drives by the evening before the trash is picked up, rummaging through stuff looking for fixable stuff and he must have taken it. A couple of weeks go by, a friend at church pulls me over to his car and says "look what I got! For free!! Doesn't work, but I thought maybe if you could fix it, you could use it." It's the Oscope I had pitched!!!! Geez!!! I can't throw it away!!!

    Anyhow, I've looked on line and can't find anything about it or schematics. Anyone know anything about SOAR corporation Oscilloscopes, model MS-6023?

    Initial damage looks like one active device (three pin thing, looks like a transistor but labeled IC)and a diode on the main board with connectors to the CRT. Two resistors burnt on the board connecting to the switches and front panel. One of them was Cooked WAY beyond identification. So, my thoughts, as well as the repair shop, are

    A) just the devices that touched the bottom metal cover are toast, fix those & it's back in business.

    B) The device that cooked on the main board going to the CRT took out something in the CRT and it may be toasted as well, and that part may be very expensive or impossible to find.

    So, Any info on Soar Corporation or this Scope would be great. If none available, well, we'll try the garbage again, but this time it'll be in a box so the scavenger won't notice it and try to "save" it!!



    Ok, so here's the current status 10/8/07

    I replaced one toasted resistor I put in a 1.5 ohm as it was measuring 1,4 and had a lot more windings on it than the .5 ohm next to it. (these were black enamel and the .5 ohm was clean and you could actually see the raised wire under the enamel. The 1.5 ohm, well it had about 3x the wire but was showing signs of severe heat)

    I also replaced the three legged device that partially popped open. It was a voltage regulator and I found a direct replacement.

    So, I now have a scope that has two traces, nice & clean.

    The horizontal position knob works as I can move the traces left & right.
    The intensity knob works ok, as it brightens & dims accordingly.
    The sweep time/variable knob seems to work ok as do the Voltage/div knobs.
    I can see chcanges in width and size of the trace/signal

    The Vertical position seems to be a problem as the traces start about 3/4" from the bottom and only move downward when the knob for either channel is rotated.

    Also, when a AC signal (from a guitar) is put to the probes, I get a distorted display. It looks like perhaps the lower half of a signal.

    So, any ideas on where to start poking around? I have had ZERO luck looking for schematics on this thing. And a search for the name of the corporation
    (SOAR Corporation) only brings up a couple of other scopes for sale or websites for some environmental group.

    Is there some sort of basic scope or TV pattern or layout to the parts that would lead me to the section of the circuitry that may be out of order?

    Any ideas are welcome

    Andy S.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    This is one of those situations where an o'scope would be very handy (snicker). If you have a meter, though, there is hope.

    Your vertical amps use both plus and minus DC. So does the vertical deflection circuit. Look things over and try to determine which is which. The vertical amps will be close to the controls, and the vertical deflection circuit may be separate from them, and have connections to the CRT. That's a bit vague about the deflection circuit, as the connections probably go through the connector at the rear of the CRT.

    That said, the first thing to do is to look for voltage test points. I've never been in a SOAR scope, but Tek has lots of labelled points on the circuit boards, as well as silkscreen labels as to function. If you can find them, check for all voltages present.

    Also look carefully at the resistors. One may be burned open, so the vertical amp or deflection circuit can swing in the positive direction. If you can identify the output from the vertical amp to the deflection, hang you meter on one set of the leads and turn the vertical adjustment control. The voltage should swing symmetrically between some negative and the corresponding positive DC level. If that happens, the failure is definitely in the deflection amp.

    After that, it's down to very careful inspection of passive components, and perhaps pulling some transistors to check junctions. Be careful, the CRT will have at least 3000 volts on it when powered up.
     
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