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BBC B+ DFS upgrade

[26th April 2014]

If you've read my BBC Micro B+ 64K page you'll know that it came with no floppy disc interface chipset fitted (quite unusual for a B+).

Here's my brief sojourn into upgrading it.

I firstly contacted an online seller RetroClinic to ask about a DFS upgrade for the 1772 which he was selling on eBay, but it turns out that it doesn't work with the B+. However, I was offered the full chipset for 1770 at a reasonable price which arrived with me in the next day.

Here's a picy of the un-upgraded mainboard:


Preparation & Notes

First order of the day is to solder some DIL (Dual In Line) IC sockets into place. There's two good reasons to do this: 1) when soldering ICs directly on to a PCB the heat from the soldering iron can destroy the chip if you take too long, 2) if an IC somehow becomes faulty then you can easy remove it without de-soldering it and fit a replacement.

The following was needed:
2x 14 pin DIL sockets
1x 16 pin DIL socket
1x 28 pin DIL socket

The kit contained the 28 pin socket, but not the 14 and 16 pin ones (I was advised of this prior to purchase so not a problem). Fortunately, I've got a small stock of these.

Speaking of the kit, here are the contents:

5x 150R resistors (R1,5,6,7,8)
1x 3K3 resistor (R14)
1x 28 pin DIL socket
1x Texas Instruments SN7438N (IC7)
1x Texas Instruments SN7416N (IC8)
1x VLSI VL1772-02PC (IC15)
1x Filing system paged ROM
1x 74LS174

Soldering / fitting the components

I fitted the sockets before the upgrade kit arrived, so the next job was to solder the resistors (R1/5/6/7/14) followed by fitting the ICs (IC7/8/16/17):


I also fitted the DFS paged ROM in a free paged rom slot (IC 35, 44, 57, 62, 68).

Finally, I had to fit pin headers for jumper positions S7 and S8. S8 was easy enough to find being sat to the right of IC7. This shows all the components fitted and a fitted and jumpered S8:


Jumper S7 was a little more difficult to locate, but I eventually found it just to the south of IC85 in the north-central part of the mainboard. I duly fitted the 3 pin header and fitted the jumper to the EAST (right) position.

BBC_DFS_Upgrade_S7notmade BBC_DFS_Upgrade_S7made


Something to note at this stage: If you forget to fit the jumpers correctly you won't get the DFS paged ROM displaying its presence on power up/reset and it won't be present when you request a *HELP listing.


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