The Journal contains the entire record image as a binary field: character type fields are ok, packed and negative signed fields and a lot of newer field types are going to remain in their binary form when you do dsp journal. Since it’s then moved to the IFS as a single field it cannot be decoded.
The journalled data needs to be restored or moved in some way on the 400 to the physical file structure that it originaled in and then it can be decoded.
It’s been a LONG time, but maybe I can get you started. I used the DSPJRN command to copy the entries to a pf as you are doing. I then looked carefully at the file using DSPPFM and found the undisplayable characters – I believe there are two bytes in the file that are in binary format. I created a query to read the file, parse out the two bytes to a shorter field, and output from the query to another pf. Then I could move the new file to my pc without any problems. Not an elegant solution, but it worked for what I needed at the time.