Oscilloscop trace at sceen bottom

[gixerags]

Hi have a problem with my Telinstruments TI5252 25mhz 2ch oscilloscope since it fell off the bench (pushed off by nutcase x partner)ch 2 is ok but channel 1 trace line i can just see at the bottom of the screen ,the position knob at its highest reaveals this and the slightest anticlockwise sends the trace down out of view...so i need to raise the trace some how to centre it..please help

 

[Harald Kapp]

so i need to raise the trace some how to centre it.

You'll need to do probably more: readjust (or recalibrate) the instrument. With a bit of luck only a trim potentiometer within the scope needs readjustment. If you're unlucky, the whole calibration has to be repeated. You'll need a servicce manual that tells you how to do this.

Note that within the scope there are dangerously high voltages, even after the instrument has been turned off (stored on capacitors). You'll have to be extra careful when opening the instrument and messing around with the circuit!

 

[Alec_t]

Welcome to EP!

the position knob at its highest reaveals this and the slightest anticlockwise sends the trace down out of view.

As Harald says, but it's also possible a fixed resistor associated with the position adjustment has come adrift.

 

[Cannonball]

You have another channel that works. I would check the voltage on the pot of channel #1 and compare channel #2 pot that adjust the vertical position. Be careful while reading voltages.

I hope this helps.

 

[(*steve*)]

It is likely to be a mechanical failure (broken solder joint, crack in a PCB, or even a fractured component).

Probing around with a plastic, glass, or even wooden rod may allow you to find a location that is sensitive to pressure.

Assuming the prodding stick is a very good insulator (don't use a pencil!) then this may be safer than measuring voltages with a meter.

 

[gixerags]

Thanks guys, will have a looksky tonight.
Thsnks all.

 

[73's de Edd]

Sir gixerags . . . . .

Considering the forthcoming and mentioned suspicions and now relating them to that specific unit of yours.
Now duly note on the supplied schematic of the Telinstruments of yours, that there is basically a set of " coarse and vernier " adjustments for trace positioning on the screen. They are being shown as the subdued PINK and GREEN annotations on the schematic.
One is being an internal coarse trim pot zero / range adjustment and your front panels position control is being the vernier adjustment.

TESTEE-TESTEE . . . . .

In the scopes no power / not plugged into AC power, condition connect an ohmmeter to the BLUE circle junction on the unaffected CHANNEL 2 and
meter neg goes to ground ( bottom leg of R1767 resistor is closest).
Log in the resistance reads made on maxed out CCW and CW positions.
Move to the complementary RED circle of your problematic CHANNEL 1 and take like reads and see if the difference in reads might give a clue as
to which end position of a control is in the greatest error and thereby relate to the forementioned causes / problems.
With the Chan 1 knob driven into the floor and circuit board micro fracture of a foil ttrace around its terminals most likely.
We proceed from that info . . . . .

The Good Stuff . . . . . .



73's de Edd . . . . .
. . . . . . . . . . .

Right now . . . it certainly seems like I'm having amnesia and deja vu all at the same time . . . since . . . I think I've forgotten this before .

 

[Cannonball]

Thanks guys, will have a looksky tonight.
Thsnks all.

You are welcome!

 

[gixerags]

Sir gixerags . . . . .

Considering the forthcoming and mentioned suspicions and now relating them to that specific unit of yours.
Now duly note on the supplied schematic of the Telinstruments of yours, that there is basically a set of " coarse and vernier " adjustments for trace positioning on the screen. They are being shown as the subdued PINK and GREEN annotations on the schematic.
One is being an internal coarse trim pot zero / range adjustment and your front panels position control is being the vernier adjustment.

TESTEE-TESTEE . . . . .

In the scopes no power / not plugged into AC power, condition connect an ohmmeter to the BLUE circle junction on the unaffected CHANNEL 2 and
meter neg goes to ground ( bottom leg of R1767 resistor is closest).
Log in the resistance reads made on maxed out CCW and CW positions.
Move to the complementary RED circle of your problematic CHANNEL 1 and take like reads and see if the difference in reads might give a clue as
to which end position of a control is in the greatest error and thereby relate to the forementioned causes / problems.
With the Chan 1 knob driven into the floor and circuit board micro fracture of a foil ttrace around its terminals most likely.
We proceed from that info . . . . .

The Good Stuff . . . . . .

View attachment 44516

73's de Edd . . . . .
. . . . . . . . . . .

Right now . . . it certainly seems like I'm having amnesia and deja vu all at the same time . . . since . . . I think I've forgotten this before .

Thanks

 

[gixerags]

Thanks.. i have only just got around to looking at this scope...my apolgies for not thanking you beforehand.
Much appreciated.