The TriMod CBM adapter now also without SMD


In the article TriMod CBM Adapter – A Commodore Floppy for Two Worlds I already presented the following adapter for the Commodore VC1541 floppy:


If you own a CBM or PET computer and want to buy a floppy drive with IEEE-488, you will surely be surprised about the prices, which have been raised on the different platforms. Fortunately there is an alternative, and that is the 1541. This drive is cheap to get and the market is virtually flooded with these drives.

Of course the VC1541 is a drive for the VIC20, C64 or Commodore 128, but Commodore had launched the 2031 drive at that time. This was basically a 1541, which was only minimally modified. So this drive had an IEEE-488 interface instead of the IEC interface.

If you look at the original schematics, the differences are really marginal, and it only takes a handful of parts to build a corresponding adapter that turns a 1541 into a 2031.

After the conversion, this floppy would of course no longer work with C64 and Co., at least not with the IEC interface.

And here comes the special feature of this adapter, because it is switchable at the push of a button. So you can use this floppy for both worlds alternately.

Please no SMD project

In a SMD version this adapter is already available for some time. But I know that not everybody likes to solder SMD. That’s why I announced back then, that I will make this adapter also in a version, which is completely without SMD components, and completely built in “THT” (Through Hole Technology / Durchsteckmontage). Of course this adapter is a bit bigger. I took this as an opportunity to integrate a corresponding kernel adapter. So you don’t need an external adapter.

The board is designed to be simply plugged on top. The MOS 6522 VIA chip and the kernel ROM have to be removed. The VIA chip is plugged onto the adapter board. Additionally an EPROM of type 27C128 or EEPROM of type 28C128 is needed. There the kernel for the IEC operating mode is burned in the first place, as the original kernel of the 1541 (or JiffyDOS and similar) and in the second place the IEEE-488 kernel of the 2031.

The construction and also the parts are analogous to the SMD board, only with the difference that instead of the SMD version here now the normal “THT” components are used. The finished board looks like this:

And from above once more:

Update (2021-03-31) / Download

The files are now available for download on GitHub:

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