Garage Sale electonic tester doesn't power on

Thread Starter

Gdrumm

Joined Aug 29, 2008
684
I found this at a Garage Sale for $1.
It looks professionally made, but simply says "Mini-Lab", with no other identifying marks that I can see.

It has 3 additional breadboards, one with several ICs.

It won't power on at all.

The fuse is good.

Any ideas about who makes it, or what it's called?

Any suggestions on where to start in troubleshooting it?

Any idea where I might find a manual for it?

Thanks,
Gary
 

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tubeguy

Joined Nov 3, 2012
1,157
I think that was well worth a dollar.

Google turned up (along with a lot of cute dogs) Orched. They make or made circuit trainers.
 

WBahn

Joined Mar 31, 2012
26,398
I wouldn't spend a whole lot of time trying to fix it unless the goal is specifically to see if you can. It looks like you got a LOT of useful pieces parts that you can use in other projects, so if you consider it $1 for a box of parts, it was a true deal.

If you really want to troubleshoot it, start by trying to identify the power supply circuits and see if you can trace them out. On something like this, you should be able to build up your own schematics fairly easily. The try to understand how they are supposed to work and start checking voltages along the circuit to see where and how they deviate from what you expect.
 

tubeguy

Joined Nov 3, 2012
1,157
From observation, it appears one transformer is center tapped, one is not.
It likely has a couple DC power supply's, one single and one split.
Start there. Check voltages on the transformer secondary's, and on the PCB with the electrolytic's

Word of caution: the AC mains seem to be on the terminal strips, so BE CAREFUL!!
 

WBahn

Joined Mar 31, 2012
26,398
Boy, I had to look about three times before I could see the brown wire from the left transformer (in the first picture).

I agree with you, which jives with the three big electrolytics on the board.

If I had to venture a guess, I would say that the right transformer goes to the left capacitor and it a +5V supply for the logic, while the left transformer goes to the right capacitors and is a ±15V dual supply for analog chips like opamps. Those may or may not be adjustable, but I'm guessing probably not.
 

Thread Starter

Gdrumm

Joined Aug 29, 2008
684
Thanks for the feedback.
I'll begin the process of checking it.
Will post back if it comes to life.

Gary
 

#12

Joined Nov 30, 2010
18,223
Piece of cake, if you're good at this sort of thing. 14 pin chips? LM723 would fit that description.
 

radiohead

Joined May 28, 2009
508
It looks home-made to me. I agree that even if it doesn't work, you still scored big with all those parts and a nice breadboard. If it won't power on, don't forget to check the switch. I've had switches go bad on me from time to time. Sometimes it can be the simple things that are overlooked.
 

studiot

Joined Nov 9, 2007
4,998
In order to check functioning as others have suggested it is wise to isolate the power supply from the rest of the layout. You need to disconnect it to do this.

The very next thing to do with any checking like this is to check for shorts across the power supplies' loads. If the unit has seen much use it is quite likely there is a short in one of the tracks, connections or breadboards. This may or may not have damaged the power supply. By splitting the unit here you will be able to prove each functional area individually, before eventual reconnection.
 

Thread Starter

Gdrumm

Joined Aug 29, 2008
684
Awesome Joe, and thanks again to everyone who responded.
The company that made the unit is in Dallas, and I was able to contact them today.

I'm expecting a call back tomorrow.

Great stuff,
Thanks again,
Gary
 

Thread Starter

Gdrumm

Joined Aug 29, 2008
684
They have a great web site if I may say so.
Google: Knight Electronic Products.
Lots of educational stuff, tools, meter, bags, etc.. with great prices.

Gary
 

Thread Starter

Gdrumm

Joined Aug 29, 2008
684
I thought I posted a Thank You Joe, buy I don't see it now.

So here is a re-post.

I was able to contact the company in Dallas, and I'm expecting a call back tomorrow.

Thanks again for all the help and suggestions.

I look forward to working on this new project.

Gary
 

JoeJester

Joined Apr 26, 2005
4,390
Gdrumm,

Not a problem. Thought it was a decent mini Lab, but it's much more than most when I found the later model. Getting that manual will help you breeze through the repairs, although they probably could be done without it.

I think you found a very nice machine.
 

Thread Starter

Gdrumm

Joined Aug 29, 2008
684
I recieved a users manual today.
Mine was apparently a prototype from 1984, but a similar unit from 2002 is comperable.

I solved the power on problem, and I'm ready to start checking it out.
It had some broken soldered joints to the power board.

It requires a multimeter, and oscilliscope, for full functionality.
Unfortunately I sold my 2 O scopes.

Anyway, I'm going to enjoy tinkering with it.
Thanks again,
Gary
 
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