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Tandon Targa TM-7521

Supposedly the first mini-tower PC, the Tandon Targa (TM-7521) was available with an 8Mhz or 10Mhz Intel 286 CPU, 1MB RAM (expandable to 5MB with a proprietary memory expansion board), 1.2MB 5.25" floppy drive, a 20MB or 40MB RLL hard disk, Tandon MS-DOS 3.2 and Microsoft Windows.

The case of this machine is quite unusual for a PC of its age - it can be used as either a mini-tower or desktop PC as two sides have rubber feet. All sides of the case are plastic so significant care must be taken when dismantling this machine as the plastic can be quite brittle after 35-40 years.

To get into the machine the rear plastic cover has to be removed by undoing the four screws in the corners and one in the center. From there you can remove the side panels by sliding them to the rear a short distance which should allow the panel to be lifted off. I do not recommend taking off the right-side panel (or left side panel when viewing from the rear) - there is nothing there except the screws for the motherboard and front plastic bezel. This panel can be challenging to get back on thanks to the rubber feet also being on this side.

Taking the left side off (or right side when viewing from the rear) allows you to add or remove expansion cards, the PSU, and drives. Expansion cards live under a metal cover which lifts off after removing four screws. To access the drives and CMOS Battery you'll need to lift the power supply out - this is achieved by loosening its three screws on the rear. When removing the PSU you'll need to disconnect not only the motherboard and drive power cables, but the grey cable going to the front panel power switch. Tandon helpfully put a connector in the cable making this easy.

This machine uses an AA size non-rechargeable 3.6V Lithium Thionyl Chloride battery for keeping BIOS settings and time. It is attached to the motherboard with zip ties and plugs in with a JST-style connector. You'll probably want to cut the zip ties and remove the battery ASAP. My machine was equipped with a Maxell brand battery - the half-AA size version of these are notorious for destroying classic Macs when they aggressively leak.

Drives are installed on rails so to slide them out through the front you've got to remove the entire front panel. Given the likely fragile nature of the plastic and how the front panel is mounted you may not want to do this as the tabs used to screw the front on break easily; most of these in my machine were already broken when I got it. Instead, with the PSU out you can remove the entire drive cage by undoing the three screws visible in the corners of the drive cage.

BIOS

These machines have a custom BIOS written by Tandon. It POSTs quite quickly and doesn't produce much output unless there are errors. In particular, it doesn't tell you what to press to get into the BIOS Setup utility or when to press it. To get into the BIOS Setup utility, press and hold the Esc key as soon as POST starts. If you do it early enough you'll eventually get an on-screen prompt offering to go into the BIOS setup utility.

The selection of options is quite limited. Only those in the top half can be changed - diskette and fixed disk drive types, keyboard and country codes, date and time, primary display type and screen saver, language, processor speed. The system load option lets you specify the boot drive or the "Menu Selection" option which gives you a boot menu after POST (pictured left).

Annoyingly the BIOS does not tell you what the drive parameters are for any of the fixed disk types and the parameters are not the same as for other BIOSes. Some DOS software claims to be able to read the drive type table from the BIOS but in my experience it doesn't work correctly here. This BIOS appears to have two different tables of drive types; one for MFM drives and one for RLL drives. Most DOS utilities only seem to be able to see the MFM table which is not helpful if you're trying to configure an RLL drive. There is also no ROM-based low level disk formatting utility.

To get available drive type information and low-level format drives you need the utilites that ship with Tandon MS-DOS. The drives.com utility (above, right) will output a list of supported drive models plus the settings for all the MFM and RLL drive types, while fxprep.exe (left) will format drives.

Strangely, the Tandon TM 264 ~40MB drive in my machine isn't listed by the utiltiy and none of the types match exactly. RLL Type 37 is the nearest match loosing only around 1MB of capacity. Sadly the drive in my machine doesn't work properly anymore though.

Keyboard

The keyboard included with this machine was an NMB RT-100+ mechanical keyboard with tactile/non-clicky Hi-Tek Series 725 key switches and a model-M style layout and case. It also includes a switch on the back for selecting either the AT or PC/XT keyboard protocol. Key caps are apparently made of PBT with dye-sublimated legends. Overall it seems to be made very well. For more information, see this review on Youtube

Documentation and Drivers/Software

If you've got a copy of Tandon MS-DOS or any scanned documentation for this machine please upload it to archive.org or get in touch (david at this websites domain). At the time of writing Tandon MS-DOS 3.x doesn't seem to have been preserved except in German (on BetaArchive), and there is no documentation available online anywhere I can find.

See Also

• Tandon Targa in the February 1987 Computer Shopper
• An Advertisement
• IDE Inc, designer of the Targas case (top entry under notable past projects)

Dismantled, cleaned, tested and reassembled April 2024. Hard disk is dead, 3.5" floppy drive needs more grease.
Battery replaced, clock not set. Case plastic is getting fragile - not much holding the front or top covers on now.