PCS500 Calibration fail

Instruments PC Oscilloscopes and Recorders
1

Hello, i damaged my PPCS500-9 scope with high voltage. Calibration failed on all ch1 and ch2. I changed IC2 and IC3 with OPA2691IDG4 and T20 T21 T22 T23 with BF556A. Signals appear on the screen now. The voltage height is right, but times not change wave lenght. Reading the frequence on the back of pcs500 i read 240Hz from 100ms to 20us and 49KHz from 5us to down at 5V. At 15V 5us read 99KHz, up ever 240Hz. Can you help me? Thanks.

Calibration results:

CH1 offset at 15V/div : 159 OK
CH2 offset at 15V/div : 153 OK
CH1 offset at 5V/div : 51 FAIL
CH2 offset at 5V/div : 51 FAIL
CH1 offset at 15mV/div : 51 FAIL
CH2 offset at 15mV/div : 51 FAIL
CH1 offset at 5mV/div : 102 FAIL
CH2 offset at 5mV/div : 102 FAIL
CH1 offset at 20us/div : -1 OK
CH2 offset at 20us/div : -2 OK
CH1 offset at 10us/div : -3 OK
CH2 offset at 10us/div : -3 OK
CH1 offset at 5us/div : -4 OK
CH2 offset at 5us/div : -5 OK
CH1 Trigger low : 98 OK
CH1 Trigger middle : 122 OK
CH1 Trigger high : 148 OK
CH2 Trigger low : 96 OK
CH2 Trigger middle : 122 OK
CH2 Trigger high : 148 OK
EXT Trigger middle : 112 OK

2

There is something wrong with the clock generator section.

I think you have the document “PCS500_Operation.pdf”.
If not, you can download it here: box.net/shared/ybz9k9adq4

There in the document please check the table labeled “The states of the outputs of IC6 at different Time/div settings are following:”.

Are all the IC6 output states OK?

3

IC6: F0 is always +5V. F1-F6 are ok.

4

This is strange.
Please check that you didn’t by mistake touch pin 16 (+5V) when measuring F0, pin 15.

5

If pin 15 of IC6 is all the time +5V then most probably IC8 (or IC6) is damaged.

6

sorry, pin 15 F0, is ok. IC6 is ok.

The wave on the screen not change. It is 2dt from 0.1us to 10us and 4dt from 20us to 100ms.

0.1us to 5us 98kHz
10us 49 KHz
20us 12.2 KHz
50us 4.88 KHz
0.1ms 2.44 KHz
0.2ms 1.22 KHz
0.5ms 488 Hz
1ms 244 Hz
2ms 122 Hz
5ms 48.8 Hz
10ms 24.4 Hz
20ms 12.2 Hz
50ms 4.88 Hz
100ms 2.44 Hz

7

[quote]The wave on the screen not change. It is 2dt from 0.1us to 10us and 4dt from 20us to 100ms.
[/quote]This is OK. The test output frequency is proportional to the Time/Div setting.
The frequencies you measured are OK.

The only problem seems to be the offset.

  • Disconnect the probes.
  • Adjust RV3 until the voltage on pin 3 of IC2 is 0V.
  • Adjust RV4 until the voltage on pin 3 of IC3 is 0V.
  • When done, select the File menu option “Calibrate & Exit”.
8

Calibration results are all ok and waves are perfect now. Frequency field, in waveform parameters, gives the wrong values of previous post (should be 98KHz for all timediv instead). I see always only two/four square waves, with more width for more timediv (should be the inverse).

9

It seems the time circuit is not working OK.
Please check the frequency on pin 16 of IC22 on all Time/Div settings.
On 1ms/div range the frequency should be 125kHz.

10

Pin 16 of IC22 has not frequency. It is always 3.6V@1ms 0.6V@50us 1.4V@5us.

11

There is frequency only when the Run button is down.
There are short pulses.

12

Next test:

  • Set the trigger on.

  • Move trigger position away from the trace to avoid triggering.

  • Click Run.

  • Check the frequency on pin 14 of IC50.
    Should be:
    244Hz at 1ms range.
    122Hz at 2ms
    48.8Hz at 5ms
    etc.

Pin14 of IC50 at 1ms/div:

13

There are not pulses on IC22 pin 16, 15, 14 (I’m using its probe, to test itself).
IC50 is ok. Trigger works on IC50 but not works on the test signal, back of pcs500.

14

[quote]Trigger works on IC50 but not works on the test signal, back of pcs500.[/quote]This is normal. Test signal can be used only when trigger is off.

Do you have any frequency counter or any other tool to check the frequency on pin 14 of IC50 ?
Should be:
244Hz at 1ms
122Hz at 2ms
48.8Hz at 5ms

You can’t use the PCS500 to check the frequency if the time circuit is defective.

15

The frequency on pin 14 of IC50 is 244hz etc., fc and pcs500 give me same values. My frequency counter has 25khz limit, I can’t use it to check pin 16 of IC22.

16

The frequency on pin 14 of IC50 indicates that everything is OK.
If the frequency on pin 14 of IC50 is OK then it is also OK on IC22.

  • No need to check.

Can you measure an external signal e.g. 1kHz or 50Hz ?
Are the displayed waveforms and the frequency reading results still wrong?

17

I tested the scope with external signals and it works fine with new calibration! :smiley: The problem is only on test signal of pcs500! May be this is normal. Thank you for support.

18

It seems everything is OK now.
I’m happy that you got your PCS500 working again :slight_smile:
The test signal is not a “normal” signal. It is internally generated from the sampling frequency and acts different way… I think OK too.