Technical Design Labs SMB TDL TESTED/WORKING Altair IMSAI Xitan S-100 S100 For Sale
Technical Design Labs SMB TDL TESTED/WORKING Altair IMSAI Xitan S-100 S100:
For sale is a repaired, tested, and working Technical Design Labs (TDL) System Monitor Board (SMB). This interface provides basically all of your I/O needs for a small S-100 system, or the foundation for a larger S-100 system. Onboard devices include:
- 2K Zapple 1.0R monitor in mask ROM
- 2K high speed static RAM
- Two serial I/O channels, RS-232 or 20 mA current loop
- 1200 bps cassette tape interface
- Parallel port
- Sense switch/IOBYTE port (on parallel adapter chip)
- Power-on jump circuitry for frontpanel-less operation
This board came to us as a "boneyard board" -- someone had removed most of the ICs and some of the discrete components. We're pretty sure this was due to a minor etch issue on the board, there was a bridge that prevented the I/O devices from selecting, which of course made the board seem "dead." There may have also been a shorted tantalum or RS-232 driver as there was a broken trace for one of the 12V Zener diodes, as seen in the third picture.All tantalum capacitors were replaced with new modern components sourced from major vendors -- we don't usually bulk recap, but tantalum failures are very common on these boards. The cassette tape connector was replaced with a right angle Molex KK-100 (KK-254) male header with polarizing ramp. The bitrate oscillator crystal was missing, and was replaced with a NOS part. This SMB has been tested in an IMSAI 8080 with the TDL ZPU Z-80 processor board.The board is currently configured to use the TTY port for console, at 9600 bps, RS-232. Power-on jump is enabled.
This card did not come with its SEMI4804 static RAM chips, and we don't currently have a source for them. These were in short supply when the TDL SMB was new, and are exceedingly rare now. TDL had to ship a mod board with some original SMBs to use slower, more power-hungry Intel 2114 type RAM chips. We have created a workalike RAM replacement, the GW-SMBRAM-2, which uses a lower power SRAM than the Intel 2114s and does not require any modification to the TDL SMB. A GW-SMBRAM-2 is included with the sale since we were unable to source SEMI4804 SRAMs.We also have reproduction Interface-1 (IMSAI spacing) and Interface-2 (Xitan spacing) I/O breakout boards available, for an additional charge. Contact us before paying if you'd like one.
Do note that the TDL Zapple monitor requires a Z80. The SMB can be modified to use a 2716 type EPROM, which would allow use of an 8080-compatible monitor, such as TDL's Apple monitor, or our GWMON-80. Please contact us if you'd like the board modified in-house for 2716s, there is no additional charge for this work.