Tenma 72-720 Oscilloscope, Where is the "TP terminal"

Thread Starter

Rocktronic

Joined Feb 17, 2022
6
I bought a used Tenma 72-720 for cheap off eBay. I got a trace and could dial it in but it was a little fuzzy and had some slight curvature at the edges on a flat line. I don't know if the electrolytics leaked out goo or if it was glue but I decided to replace all the electrolytics to be safe.
Now I'm trying to perform the calibrations listed in the manual and there are instructions to short or open the TP terminal on the V PCB.
I can't find a "TP terminal" on the Vertical Amplifier board or elsewhere in the literature.

Does anybody know where or what that terminal is?

I attached the manual. Pg 18, section 5.

Thanks
 

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KeithWalker

Joined Jul 10, 2017
2,351
I bought a used Tenma 72-720 for cheap off eBay. I got a trace and could dial it in but it was a little fuzzy and had some slight curvature at the edges on a flat line. I don't know if the electrolytics leaked out goo or if it was glue but I decided to replace all the electrolytics to be safe.
Now I'm trying to perform the calibrations listed in the manual and there are instructions to short or open the TP terminal on the V PCB.
I can't find a "TP terminal" on the Vertical Amplifier board or elsewhere in the literature.

Does anybody know where or what that terminal is?

I attached the manual. Pg 18, section 5.

Thanks
Is this it?

New-1.jpg
 

Thread Starter

Rocktronic

Joined Feb 17, 2022
6
Awesome, thanks. I missed that. I found it on the board. TP next to a rectangle with three holes (ports) and line dashes pointing to one of the holes and a pin on an adjacent connector.

I guess that means to jumper the center hole and the first (nearest) pin on that connector?
 

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Thread Starter

Rocktronic

Joined Feb 17, 2022
6
That dashed line actually extends past the connector over to a white wire soldered to the board and the other way to either to a capacitor or maybe all the way over to the other end of that wire which is also connected to the board,

I wonder if that wire is already shorting the TP or is it just the two holes in the rectangle that are closest together?
 

Thread Starter

Rocktronic

Joined Feb 17, 2022
6
I found the dashed line on the layout as well, it does extend between the two ends of a white wire.

So, is that wire the jumper between the test points, or just indicating a jumper?
Which terminals should I short?

Thanks
 

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Thread Starter

Rocktronic

Joined Feb 17, 2022
6
When I look closer at the layout, it only shows the two outer holes within the box while there is a third hole within the box on the actual board. Now I think it's either those two outer holes within the box or the white wire connected at each end of the dashed line.

Does the "TP" signify the box or the dashed line?V-PCB2.jpgTP.jpg
 

KeithWalker

Joined Jul 10, 2017
2,351
In the diagram it shows solder pads only on the two holes at the ends of the TP rectangle. I would think they are the two points to be shorted together. I would solder in a couple of test pins to them so I could access them without shorting out anything else.
 
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