Is this gonna haunt me!?!?!

[Andy S.]

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!!

Thanks,

Andy

[Don Moose]

Well, the 3-legged thing is most likely a linear voltage regulator - those are generally cheap and easy to get.

My vote, if you can lay your hands on some kind of schematics and/or BOM, steadily replace bits as you identify them as being problems. At some point, you'll have learned some things, and have a functional scope for approximately free, or just have learned some things and hit your limits for patience or budget.

Best of luck!

[Andy S.]

Originally Posted by Don Moose

Well, the 3-legged thing is most likely a linear voltage regulator - those are generally cheap and easy to get.

My vote, if you can lay your hands on some kind of schematics and/or BOM, steadily replace bits as you identify them as being problems. At some point, you'll have learned some things, and have a functional scope for approximately free, or just have learned some things and hit your limits for patience or budget.

Best of luck!

Don, (or anyone else who may want to venture a guess or pass along info)

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 works ok, as it brightens & dims accordingly.
The sweep time/variable knob seems to work ok as do the Voltage/div knobs.

The Vertical position seems to be a problem as the traces start about 1" 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.

[Don Moose]

It sounds like the channel preamp has at least a couple of issues.
I assume you're meaning the trace only moves down when you play with the vertical scale knobs - if that's not right, we can look at some other ideas.

- Is there a 'vertical position' or offset knob? Does it do anything?

- Is there an AC/GND/DC switch for the input (the AC position AC-couples the input for looking at DC-biased signals)? Does it do anything?

- Does the distortion look clipped on the high side? Only on the high side?
that would have me thinking about the power supply or the biasing in the preamp.
then about the components there - does anything look toasted? are there any 'lytic caps that look leaky?

About the circuit 'pattern':
There's a preamp with an attenuator or programmable gain (vertical scale) and an output bias adjustment (vertical position). That preamp drives the vertical deflection amp, which does something to the (I'd assume) top and bottom deflection plates on the tube.

There's another output from the preamp that goes to the trigger section, which also has some other modes.

Then there's the timebase and sweep generator it controls - these drive the horizontal amp, which do something to the (most likely) left and right plates on the tube.

The timebase is triggered by the trigger section.

- but hey, you knew all that already. The only things to worry about are the voltages involved and the precision of the components.

Hope this helps!

[Andy S.]

Originally Posted by Don Moose

..................................... but hey, you knew all that already. ..................
Hope this helps!

Uhm...yeh! I knew that ! yeh, I knew all that stuff.....uh-huh! That's my story and I'm sticking to it.

NOT!!!!

I had a very slight hunch about the positive side of the PS. But that's pretty much it. I had been looking for any additional toasted components that I may have missed the first time, but everything looks clean.

I truly appreciate the info and the suggestions. I'll keep you all posted on any progress!

[HardRockHenry]

That's crazy , He just let you have it ? Didn't have you send it back ? Pretty trustworthy , or knew it was broken.

[Andy S.]

Pretty trustworthy , or knew it was broken

I had corresponded with him prior to the sale. He had gotten several scopes from some business that had closed and this was old stuff stored in back. I think he also knew the way it was packed that it could have been susceptible to having the bottom or top pushed inward a bit. That's what happened. He was good about it, so I vote for the trustworthy category.