Tandy 5000 MC Troubleshooting Guide

Layout of the 5000 MC main logic board (8899061) from Ardent Tool, with the power connector J7 pin numbering at right.

Fault finding on the Tandy 5000 MC relies on Radio Shack's faxback service documents, Ardent Tool of Capitalism's board notes and owners' reports; Tandy's technical reference for the machine has not been found online, so there are no schematics or test procedures. Routine settings are in the Tandy 5000 MC General Maintenance guide.

Start-up faults

Tandy 5000 MC start-up faults

Symptom	Likely cause	What to do
Configuration error after storage; settings and time lost	The lithium cells in the DS1287A (U19) and DS1220Y (U11) are exhausted	Replace both modules, then start from the reference diskette and restore or automatically configure
Asks for configuration after a card is added or moved	Adapter description files not installed	Install the card's files on the working reference diskette and run Automatic Configuration
Memory errors after a memory change	S1, S2 or the E9-E17 jumpers do not match the memory fitted, or mixed SIMM sizes	Set them from the table in the maintenance guide; use one SIMM size throughout
Dead at switch-on	Power supply fault reported by one owner	Check the supply and the J7 rails (below)

Beep codes

Ardent Tool lists Radio Shack's beep code sheet with the 5000 MC documents. Radio Shack describes it as a general list for most AT-compatible computers, sounded only for fatal faults found before the screen has been initialised; the first entry still names the 80286 register test. A code such as 2-1-4 is a burst of two beeps, one beep and a burst of four.

Selected codes from Radio Shack's beep code list

Code	Test in progress or failed
1-1-3	CMOS write/read
1-1-4	BIOS ROM checksum
1-2-1	Programmable interval timer
1-2-2	DMA initialisation
1-2-3	DMA page register write/read
1-3-1	RAM refresh
1-3-3	First 64K of RAM, multi-bit fault
1-3-4	First 64K of RAM, odd/even logic
1-4-1	First 64K of RAM, address line
1-4-2	First 64K of RAM, parity
2-1-1 to 2-4-4	First 64K of RAM, data bit 0 (2-1-1) to bit F (2-4-4)
3-1-1 to 3-1-4	Slave and master DMA registers, master and slave interrupt mask registers
3-2-4	Keyboard controller
3-3-4	Screen memory
3-4-1	Screen initialisation
3-4-2	Screen retrace
Long, short, long, short	No video adapter found
Long, long	No boot device

Source: Radio Shack's list.

Power

The supply is rated at 192 W and runs from 105 to 130 V AC at 60 Hz. It feeds the main board on J7:

Main board power connector J7

Pins	Signal
1, 2, 4, 5	+5 V
3	+12 V
6, 7, 8, 9	Ground
10	−5 V
11	−12 V
12	Power Good

Source: Ardent Tool's board notes. The drive power connectors carry +12 V on pin 1 (orange), ground on pins 2 and 3 (black) and +5 V on pin 4 (red). Fuse F1 (1 A) on the main board is fitted to the Canadian version only. No output tolerances for the supply have been published.

1. Remove the expansion cards and memory cards, leaving the CPU card, and try again.
2. Unplug J7 and check the board side of each supply pin for a short to ground.
3. With J7 connected, measure +5 V, +12 V, −5 V and −12 V at the connector and check that Power Good goes high.

Video

VGA is on the main board: an Intel 82706 (U67) with an INMOS IMSG176 RAMDAC (U47), 64K x 4 video RAM, and 25.175 MHz and 28.322 MHz oscillators (Y2 and Y3). Radio Shack's pinout sheet gives the DB-15 monitor connector, with pin 5 as self test and pins 13 and 14 as horizontal and vertical sync; a monochrome monitor uses pin 2 for its signal, a colour monitor pins 1, 2 and 3 for red, green and blue. Tandy's own monitors were the VGM-100 monochrome and the VGM-200 and VGM-300 colour models.

Keyboard, mouse and ports

Keyboard and mouse connectors (Radio Shack faxback 1725)

Pin	Keyboard	Mouse
1	Data	Data
2	Not connected	Not connected
3	Ground	Ground
4	+5 V	+5 V
5	Clock	Clock

Radio Shack lists five pins; BYTE describes both as 6-pin DIN connectors. The keyboard controller is an 8742 (U2) and the serial port uses an NS16550A (U31) with a 1.8432 MHz oscillator (Y1). The parallel port can be set as compatible (output only) or extended (bidirectional) and uses IRQ 7. Under SCO XENIX 2.2.4 or 2.3.2 GT, the CMOS setting Printer-1 is XENIX port lp1 and Printer-2 is lp0.

Floppy and hard disk

• The 82072 floppy controller (U64), with a 24 MHz oscillator (Y4), supports 360K, 720K, 1.2 MB and 1.44 MB drives but not 2.88 MB.
• The floppy header carries +5 V on pins 5, 7, 9 and 11 for the 3.5-inch drive; it is not available to a 5.25-inch drive.
• Hard disks were sold with ST-506, ESDI or SCSI Micro Channel controllers. See Hard Drive Maintenance and Repair.

Capacitors

See the Tandy 5000 MC Capacitor Replacement Guide and Capacitor Failure Symptoms.

Related pages

• Tandy 5000 MC
• Tandy 5000 MC General Maintenance
• Tandy 5000 MC Capacitor Replacement Guide