PCSU1000 Sometimes a signal is displayed in GND mode?

Instruments PC Oscilloscopes and Recorders
1

Sometimes a signal is displayed in GND mode ?

Is it normal ?

2

In what case this happens?

3

It happens sometimes in normal conditions.

4

These may indicate that the relay RY12 is not working properly.
During the calibration the coupling is set to GND. If this is not the case it may result poor calibration results and cause the trace jumps when the Volts/div setting is changed.

5

I can ear the “clic” of the relay when switching from AC to GND.

Do I have to send back the oscilloscope to the distributor (Farnell) ?

6

You may first download the new v3.07 of the PC-Lab2000SE software.
In this version the probe input is disconnected when the GND setting is selected.
With this new software you can easily see if the relay is not working properly: When the GND is selected the trace will move out of the screen if the relay is faulty.
That will be clear indication of the fault and you can send the oscilloscope to repair.

7

Dear VEL255,

I first must commend you guys at Velleman for having these forums and making such fine kits and test gear (which is affordable for young people like me - I’m in my 2nd year at University studying Electrical Engineering). Initially I couldn’t afford a good 'scope until I came across the PCSU1000 - which an ElecEng graduate offered me at a reduced price, second hand.

Now that I’ve been playing around with it - I’ve updated to the latest software from the site as of yesterday - there’s massive problems with CH1. My ground relay probably has failed – setting the CH1 coupling mode to GND and contacting the probe with the test point at the rear of the scope produces a fine squarewave! Also, when nothing is connected we get this wild oscillation of some sort on the screen.

Upon updating the software - I’ve had massive problems with calibration on CH1 - with Low Trigger failing, and usually 0.5V/div offset at 51 FAIL.

I think the first owner may have been playing around with it - it’s noticeable he had adjusted the trimpots – the accuracy in terms of voltage of the first channel is about 10% low.

I’m in Australia and I don’t know if I can obtain service for it (or afford to send it back to service given that it was just within my budgets to obtain it) - and was wondering if you could give me any pointers as to what part the relay is - and which trimpots need adjustment - i.e. which trimpots control offset, gain, trigger levels?

I hope that you can help me.

Thanks,

  • Gough
8

Nice that you like the PCSU1000 as a test gear.
Sorry that your unit seems to be somewhat defective anyhow.

It seems that the relay RY12 is defective.
You can see the PCB lay-out and the location of this relay in the document PCSU1000-4_PCB.pdf on the companion CD.
The circuit diagram document is PCSU1000-4_SCH.pdf.
If you like to change the relay by yourself you need good desoldering tool.

You can use trimpot RV2 to adjust the gain of CH1.
All other adjustments are made by the software and they fail due to the faulty relay RY12.

9

Do you know who makes the relay and where I can obtain one? Desoldering is no trouble - I have experience repairing multilayer computer motherboards (the bad capacitor plague) so that should be easy to replace as long as I can find out where to buy some.

10

Please provide an address. As a one time courtesy, we will send a relay

11

Sorry, as I’ve been away on holidays I forgot to check the messageboard.

Thank you very much for the offer, how should I contact you to provide you the address (as posting it on a public message-board is probably not a wise idea, and the personal message system has been disabled :().

Thanks again!

EDIT: EDIT: Removed Edit to prevent spamming.