Amrel PPS 2322 GPIB communication problem

[jordannedev]

Hi every one!
I have very strange problem with my Amrel PPS 2322 power supply.
I bought it before 4 weeks from Ebay an till now I can't find from where is the problem with GPIB communication. First when I bought it I find that on boot on the display shows PPS 1203. I bought new 27C512 EPROM and I flash it with the bin file from Kerry D. Wong blog http://www.kerrywong.com/2018/01/07/amrel-pps-2322-programmable-power-supply-firmware-backup/ and everything else except the GPIB communication is working just fine. The code that I'm using is

Code: [Select]

import pyvisa
import time

rm = pyvisa.ResourceManager()
print(rm.list_resources())
supply = rm.open_resource('USB0::0x03EB::0x2065::GPIB_12_850323137363517141A0::INSTR')

supply.write('VSET1 10.0')
supply.write('ISET1 0.5')
supply.write('VSET2 12.0')
supply.write('ISET2 0.5')

supply.write('OUT1 1')
supply.write('OUT2 1')

When I connect the GPIB to USB adaprter on the front panel of the power supply I get indication for remote "RMT" operation and I'm able to see it as device in NI MAX with the correct address. I see it but there is no communication. I get error that "Timeout expired before operation completed". I try with different end characters with out any succeed.
I have also Amrel PPS 18-4 that works perfectly fine with the same code.
I found this very useful information here https://www.eevblog.com/forum/testgear/motech-amrel-pps-1002-diagramschematic/.
Based on that I made some measurement with the logic analyser and I found that the NAT7210 CS pin stay always high no mater what I do with the power supply. I replace the GPIB driver ICs SN75ALS160/161 with new one. I trace the pcb and I did not find any interrupted traces. I check 74HC373 and it is working.
The pin connections are exactly the same as shown in the schematic diagram in the post.
Can some one, who have the same power supply, to read the CPLD GAL16V8B?
If you have any other ides what may cause the problem please share 

[coromonadalix]

pls put a black tape on your eeprom window

[jordannedev]

The EEPROM have already black tape, don't worry about that

[jordannedev]

Any suggestions?

[Andy Watson]

How does the power supply store calibration and GPIB settings? Is it possible that these have been corrupted?
Can you check that it is set to gpib address 12. And that the overvoltage trip levels are not set at zero.

[rcjoy]

Check for continuity between each pin at the GPIB port and the connector on the board.

I've had those IDC ribbon cable GPIB connectors fail, and in my case it was also on an Amrel PPS
power supply.  One of the data I/O bits was open.