Dejan and I have finally managed to perform one last attempt to fix the Hammond XB-2. As said in my previous blog post, the XB-2 I bought had an interesting distorted sound problem. This is a video of the sound problem:
We tried a number of things, including the DRAM swap.
Today, we performed the SRAM swap. Since we were not able to obtain the 16kbit chip equivalents to original, we took 64kbit chips and made a pin adapter.
The original chip is V61C16 Vitelic (see datasheet here: http://www.datasheetcatalog.com/datasheets_pdf/V/6/1/C/V61C16.shtml)
The 64kbit alternative has 4 more pins – we linked the A11 and A12 address pins to the ground.
We used the IS 61c64 chips (datasheet: http://pdf.datasheet.live/006fc7c7/issi.com/IS61c64-L20N.pdf).
We took 2 dual inline (DIL) sockets and linked the matching pins directly. For other pins, we cross-linked the pins with wires (mostly to VCC and GND).
We tested each socket on the main board independently and tried out both 16kbit chips which Dejan took off the main board.
Unfortunately, there was no difference in the sound.
As a final attempt, we added new capacitors to all RAM chips.
This concludes the work on this Hammond. We became experts in several aspects. However, we will not pursue this issue further. Apparently the problem is either in the DRB or MUSE chips, which are impossible to find. The Hammond will become a second midi keyboard (second manual) to my Roland VK-7. The latter is currently also in pieces. I am trying to remove the dripping red glue which holds the key weights in place beneath the keyboard. More on that in a few days …