Calibration failed PC scope PCS500

Instruments PC Oscilloscopes and Recorders
1

Hello!

I was about using my Pcscope after a long time of not used it,
it worked fine last time i used it, but now i get an error that says
Callibration failed.
I have tested it on thre computers but all got the same error.

The logfile look like this.

Calibration results:

CH1 offset at 15V/div : 280 FAIL
CH2 offset at 15V/div : 280 FAIL
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 : -24 OK
CH2 offset at 5mV/div : 102 FAIL
CH1 offset at 20us/div : 201 FAIL
CH2 offset at 20us/div : 201 FAIL
CH1 offset at 10us/div : 201 FAIL
CH2 offset at 10us/div : 201 FAIL
CH1 offset at 5us/div : 201 FAIL
CH2 offset at 5us/div : 201 FAIL
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

I downloaded the elektrical chematic but i am not that good at this but it seems that +5V is ok but i got this result from meassuring IC1 LM2990T Ground to input -1.7V Ground to output 0.8V this couldn´t be right or what??
I didn´t find IC1 in the chematic:-P

Would be greatfull for any help i can get!

Jens

2

The results you got indicate that the charge pump in front of the IC1 is not operating.
The output voltage from IC1 should be -5V.
You’ll see the IC1 and the charge pump on page 6 of the circuit diagram.
Here is a link to download the complete circuit diagram and operation description:
box.net/shared/ybz9k9adq4

3

Chargepump is it all things before IC1?
The input to IC1 should it be +5V?
Anny suggestion where to meassure:-P

4

[quote]Chargepump is it all things before IC1?[/quote]Yes. IC45D is the oscillator for the charge pump. The charge pump contains the parts: T4, T6, T7, T14, T15, C13, C16, C19, D26, D27, D28, D29 and C24.

[quote]The input to IC1 should it be +5V?[/quote]No. It should be about -7.5V.

[quote]Anny suggestion where to meassure:-P[/quote] You may start from the oscillator. Check if it is oscillationg. If you haven’t other oscilloscope, you may measure the voltage on pin 8 of IC45 with a DVM. The voltage should be about 2.15V.

Next you may measure the voltage on the collector (the large pin) of T14.
Should be about +4V.

5

You where right i dont have any other scope:-(
But i did the suggested meassurement and i got 4,8V on IC45 pin 8, and i got 5V on T14 collector.

6

These are strange results.

7

Are you sure you measured the voltage on pin 8 of IC45 ? (The pin on the top right corner of the IC.)
According to the result you got from the collector of the T14, the charge pump may be working. There may be defective electrolytic capacitor.

What is the input voltage (on pin 2) of IC1? Is it really +5V, as you wrote. This is very strange too.

8

Have you checked the power supply for the PCS500?
To make sure it’s out putting clean power?

Maybe try another power supply of the same voltage and current?

Just a thought.