Faulty PCS500

Hello,

We’ve had a PCS500 for a couple of years and it has been fine until recently. It started prducing spurious spikes/noise on CH1.

It starts up ok, when I boot the PC and run PC Lab2000 the scope LED goes from off to on and the traces appear on the screen when RUN is pressed. But when I try to measure a signal I get lots of spikes and noise on the trace. So then I go into the Hardware setup menu, click OK and the program goes through the calibration sequence. This now seems to take longer than before and at the end of it I get a dialogue error message saying “CALIBRATION FAILED. Please check calibraion.log file for more details.”

When I open the calibration.log file I see the following:

"Calibration results

CH1 offset at 15V/div: 116 OK
CH2 offset at 15V/div: 123 OK
CH1 offset at 5V/div: 2 OK
CH2 offset at 5V/div: 2 OK
CH1 offset at 15mV/div: 4 OK
CH2 offset at 15mV/div: 1 OK
CH1 offset at 5mV/div: 13 OK
CH2 offset at 5mV/div: 5 OK

CH1 offset at 20uS/div: -1 OK
CH2 offset at 20uS/div: 0 OK
CH1 offset at 10uS/div: -4 OK
CH2 offset at 10uS/div: -3 OK
CH1 offset at 5uS/div: -4 OK
CH2 offset at 5uS/div: -3 OK

CH1 trigger low: 128 OK
CH1 trigger middle: 128 FAIL
CH1 trigger high: 128 FAIL

CH2 trigger low: 128 OK
CH2 trigger middle: 128 FAIL
CH2 trigger high: 128 FAIL

Ext trigger middle: 128 OK "

Any ideas why the unit might be behaving this way and what it causing CH1 & CH2 triggers to fail?

Any help much appreciated.

Thanks,
Dave.
(Lancaster University, England)

Sorry about the trouble. It is very difficult to say what might be wrong.
First check that the +5V on the PCB is OK.
Close the program.
Open WinDso.ini file (in PC-Lab2000SE folder if you have downloaded the latest software, otherwise in PC-Lab2000 folder) and replace the [Calibration_500] section of the file with the following text:

[Calibration_500] trg_ch1_min=100 trg_ch1_mid=128 trg_ch1_max=156 trg_ch2_min=100 trg_ch2_mid=128 trg_ch2_max=156 trg_ext_mid=85 offs_1=128 offs_2=128 v5_offs1=0 v5_offs2=0 v15mv_offs1=0 v15mv_offs2=0 v5mv_offs1=0 v5mv_offs2=0 f5us_offs1=0 f10us_offs1=0 f20us_offs1=0 f5us_offs2=0 f10us_offs2=0 f20us_offs2=0 Ch1_pos0=128 Ch1_pos1=32 Ch1_pos2=224 Ch2_pos0=128 Ch2_pos1=32 Ch2_pos2=224 Ch1_ad0=128 Ch1_ad1=62 Ch1_ad2=192 Ch2_ad0=128 Ch2_ad1=62 Ch2_ad2=192
Save the file.
Run PCS500.EXE program. The oscilloscope should not calibrate now. Click the Run button.
Check that the Y-position adjustments are working OK.
Set the trigger on and move trigger point to somewhere at the upper or lower section of the screen. Move trace’s Y-position over the triggering level (up and down): Does the triggering occur?

Does the trigger occur on the channel 2 normally if you feed some signal to it?

Hi, thanks for your reply.

I made the changes to the file as you suggested and ran PCS500 and it seems to work ok. But this is just the PC based demo isn’t it?

The +5V reg seems ok on the scope, 9V in, 5V out.

I’ve taken a screen shot of both traces running on startup settings with no probes connected and you can see a lot of (maybe digital) noise mainly on CH1 but some on CH2 too. Can I email this for you to have a look at?

With a probe connected I

Thanks,
Dave

Please mail the screenshots to support at velleman.be
This address will accept your message only once. Do not attempt to send multiple messages, they will be discarded. We will forward your message to the designer.

  • I tried sending the screen-shot to that email address and got a ‘delivery failed’ message. Is that the correct address?

Dave.

Yes, that is the correct address. It is working fine.

Better to start the PCS500 scope from the Pc-Lab2000 startup screen to prevent it from going to the demo mode.
The values of the section [Calibration_500] that I sent are the default calibration settings for the PCS500 oscilloscope.
The self calibration of your scope fails and bad calibration values are written to the WinDso.INI file.
If you now go again to the Hardware setup menu and click OK then the scope goes through the self calibration and writes new (bad) values to that section of the file. May be useful to compare the values of the [Calibration_500] section after the self calibration to the default values.