BK Precision 9129B Serial

[jgrossman]

note: throughout, "not working" means "I can see UART on the scope, but no response from the unit"

Hey eevblog forum, I recently acquired a used BK Precision 9129B power supply. I am trying to use the serial interface. Neither I nor the seller knows if the interface was working at the time of purchase. I was trying to use the DB9 connector with a USB-RS232 bridge but missed the probably 5 warnings that the DB9 is a TTL level interface, not a standard RS232 level (nice prank, BK . This is my error, but who does this???)

I quickly realized the mistake and fashioned an FTDI serial to USB converter to try instead, but that did not work either. I sucked it up and bought the original IT-E312B adapter, thinking there may be some special sauce I was missing since it never actually states in the documentation that you can actually use anything else. No dice on that either, and cracking it open I didnt see anything special, just a PL2303TA serial-USB bridge and an isolator.

I'm starting to suspect I have (unsurprisingly) damaged something while trying to use the USB-RS232 bridge. Buzzing out the DB9 comm. pins, they are in series with a 10 Ohm resistor, then straight into an STM32... great. I installed the debug header and dumped the contents of the STM32, but before I just go for broke and replace the STM32, I was hoping somebody could either point me towards a service manual or advise some additional troubleshooting I can do to narrow down where the issue actually is.

Has anybody actually used the serial interface on this? The manual says that the display will show "RMT" when successful connection is made over the serial, but I have no idea how it can even determine that, since it supposedly does not have flow control (or at least, the manual claims so)

[jchw4]

I had never have any experience with this particular model but earlier BK power supplies of the same class suggested using IT-E131 USB to RS-232 cable. If you google it you will find that it is ISOLATED conveter.

This was important because connecting anything to RS-232 effectively made the first channel USB-referenced.

IT-E131 is not explicitly marked isolated but I would not be surprised that it is in fact isolated.

> DB9 is a TTL level interface, not a standard RS232 level (nice prank, BK . This is my error, but who does this???)

I think it is reasonable to assume that modern "RS-232" ports are always TTL.