Hello…
I think my scope Input1 is dead (while the Input2 seems OK), but I have no idea on which component is broken:
When I give a square input signal of 5V on Input1, there is nothing visible except in 15V/div where I get a very small signal with an important positive offset (signal at top of screen).
The calibration fails, and here the log:
Calibration results:
CH1 offset at 15V/div : 239 FAIL
CH2 offset at 15V/div : 125 OK
CH1 offset at 5V/div : 51 FAIL
CH2 offset at 5V/div : 4 OK
CH1 offset at 15mV/div : 51 FAIL
CH2 offset at 15mV/div : 3 OK
CH1 offset at 5mV/div : 102 FAIL
CH2 offset at 5mV/div : 68 FAIL
CH1 offset at 20us/div : -2 OK
CH2 offset at 20us/div : 0 OK
CH1 offset at 10us/div : -3 OK
CH2 offset at 10us/div : -2 OK
CH1 offset at 5us/div : -3 OK
CH2 offset at 5us/div : -3 OK
CH1 Trigger low : 98 OK
CH1 Trigger middle : 124 OK
CH1 Trigger high : 130 FAIL
CH2 Trigger low : 100 OK
CH2 Trigger middle : 126 OK
CH2 Trigger high : 152 OK
EXT Trigger middle : 113 OK
Since it appeared short after switching to PcLab2000SE, I thought of a software issue. I then went back to PcLab2000, but with same result.
Could you give me any instruction/advice on which component to look at/check?
Hello Vel255,
Your opinion is 100 % OK : The voltage on pin 3 of IC2A is 0.92 V in place of 0,0 V, and the voltage on pin 1 of SST441 is 2.44 V in place of 1.6 V. The values for input 2 are OK. So, does Velleman provide this SST441 ? If yes, how to order this device ; If not, have you an idea where to buy 1 or 2 items ?
Many thanks for your help.
Rakam
Thank you for the shipment, I’ve just soldered the parts…
After calibration, all functions seem to work properly on both inputs, for any sensitivity.
Here is the calibration result: CH1 offset at 15V/div : 115 OK
CH2 offset at 15V/div : 124 OK
CH1 offset at 5V/div : 1 OK
CH2 offset at 5V/div : 3 OK
CH1 offset at 15mV/div : -3 OK
CH2 offset at 15mV/div : 3 OK
CH1 offset at 5mV/div : -9 OK
CH2 offset at 5mV/div : 11 OK
CH1 offset at 20us/div : -1 OK
CH2 offset at 20us/div : 0 OK
CH1 offset at 10us/div : -3 OK
CH2 offset at 10us/div : -3 OK
CH1 offset at 5us/div : -3 OK
CH2 offset at 5us/div : -3 OK
CH1 Trigger low : 100 OK
CH1 Trigger middle : 126 OK
CH1 Trigger high : 152 OK
CH2 Trigger low : 102 OK
CH2 Trigger middle : 128 OK
CH2 Trigger high : 154 OK
EXT Trigger middle : 113 OK
Nevertheless I noticed some differences in voltages and resistor values onto the PCB (which is identified as PPCS500-9):
The original broken part was a SST441 while the new one is a SST440. I don’t know if it can have consequences…
After I adjusted the pin 6 at 0,000V with RV3, the voltage at pin 1 is 0,64V (in place of 1.6V), an the voltage at pin 5 is –4.33V (in place of –3.4V).
The actual resistors on PCB are different from those in technical documentation:
R4 is 2000 ohms in place of 422 ohms
R5 is 1500 ohms in place of 402 ohms
RV3 is 100 ohms in place of 50 ohms
Is there any precaution/check/change I should do? Is it reliable like this for the long term?
Thanks a lot for your great support… It’s rare to find one of this quality nowadays!
Rakam
Good to see that you got the scope working!
The SST440 is perfect replacement to SST441. Actually the SST440 is slightly better one.
See the datasheet: linearsystems.com/datasheets/U440.pdf
The only difference is in the “Differential Gate to Source Cutoff Voltage”:
SST441: 20 mV
SST440: 10 mV
This new FET seems to have lower “Gate to Source Cutoff Voltage” than the SST441.
This is no problem. You see in the datasheet that the variation range is large: -1V to -6V.
Indeed some resistor values are changed:
They are:
R4 is 200 ohms in place of 422 ohms
R5 is 150 ohms in place of 402 ohms
RV3 is 100 ohms in place of 50 ohms