Before noticing your post, I had removed my 1MB PCB RAM and replaced it with 4MB in my GVP A2000-030 COMBO REV 3
25MHz version, but so far it has not been a great success. Here are the pictures
http://relay.pp.fi/Amiga/A2000/GVP A3000-030 COMBO REV 3/ and here is how I ended up doing that:
I got the card with a faulty status.
In electronics microscope inspection I found track cut above RP4 (resistor network) in the highest running track of the PCB. The track ended to U6 MACH130 pin 73, so surely it was crucial to operation. The cut was very likely created when some object dropped over the cards top edge, because there was not just a track cut but also deep "pit" in that spot.
I repaired the cut and the card started to operate.
I bought eight NOS Hitachi HM514400
CS6 chips from Ebay. These chips are 512k each so they should create 8x512k=4096k=4MB.
This has 4MB and it has HM514400
AS6. So I am sure I have compatible chips.
I removed the original 1MB from PCB and carefully cleaned and inspected the pads.
I then soldered the new ones and it was really painful even under electronics microscope, because the pads are a little bit offset and a lot of tracks go between the chips pins.
Then I tested and noticed the card still shows 1MB and not 4MB. I also tested installing 030 50MHz and jumpering the card for it, but no luck.
My conclusion is that the my U34-U40 chips have too "old" .JED in them and 40/50MHz card used newer .JED which enable 4MB PCB RAM.
Here are some fruits of the research I started:
http://relay.pp.fi/Amiga/A2000/GVP A3000-030 COMBO REV 3/GVP A2000-030 COMBO.html
I'm planning to sell this card here on Amibay as soon as I have either solved this "problem" or given up trying.