Jump to content

Tandy 1000 EX Capacitor Replacement Guide

From RetroTechCollection
Tandy 1000 EX 28 W power supply 8790083 schematic (Technical Reference Manual)
The EX's 28 W supply 8790083. The output electrolytics are on the right: C9 and C10 on +12 V, C11 to C13 on +5 V, C14 and C15 on -12 V.

Tandy published every capacitor in the Tandy 1000 EX: the Tandy 1000 EX Technical Reference Manual (catalogue no. 25-1510) has parts lists for the main logic board, both versions of the 28 W supply, the Memory PLUS adapter and several option boards.[1] The supply holds the large electrolytics; one owner brought a dead EX supply back by replacing all of them.[2] See Capacitor Failure Symptoms for the signs of a failing part.

[3]

Single-input supply 8790083

[edit | edit source]

Values from Tandy's parts list; positions from schematic 3P-M1-0163.[3]

8790083 electrolytics
Ref Capacitance Rating Position
C4 220 µF 200 V Primary reservoir, after bridge D1
C9 1000 µF 16 V +12 V, after rectifier D6 and ahead of choke L2
C10 470 µF 16 V +12 V output, after L2
C11, C12 4700 µF 10 V +5 V, after rectifiers D9 and D10 and ahead of choke L3
C13 1000 µF 16 V +5 V output, after L3
C14 330 µF 35 V -12 V, after rectifier D11 and ahead of regulator IC1
C15 100 µF 25 V -12 V output, after IC1
C17 1 µF 50 V Gate circuit of the crowbar thyristor SCR1

The other capacitors are film and ceramic: C1 and C2 (0.1 µF 250 V AC film) across the mains, C3 (10000 pF 400 V AC), C5 (0.01 µF 400 V AC film), C6 (680 pF 2 kV), C7 and C16 (0.1 µF 50 V film), C8, C22 and C23 (0.047 µF film), and C20 and C21 (2200 pF 400 V AC ceramic).[3] If C1 or C2 is replaced, use an X-class safety capacitor rated for the mains.

Dual-input supply 8790086

[edit | edit source]

Values from Tandy's parts list; positions from schematic 3P-M1-0159.[3]

8790086 electrolytics
Ref Capacitance Rating Position
C6, C7 100 µF 200 V Primary reservoir
C12 1000 µF 16 V +12 V, after rectifier D9 and ahead of choke L2
C13 470 µF 16 V +12 V output, after L2
C14, C15 4700 µF 10 V +5 V, after rectifiers D11 and D12 and ahead of choke L3
C16 1000 µF 16 V +5 V output, after L3
C17 330 µF 35 V -12 V, after R13 and D13 and ahead of regulator IC1
C18 100 µF 25 V -12 V output, after IC1
C20 1 µF 50 V Gate circuit of SCR1

Main logic board

[edit | edit source]

The main logic board (subassembly 8859000) has twelve electrolytics, all axial and all rated 16 V. The other capacitors are ceramic and monolithic decoupling and timing parts and one 0.022 µF polyester capacitor (C127).[4]

Main logic board electrolytics
Ref Capacitance Rating Type Tandy part no.
C102, C103, C110, C114, C133, C134, C169 22 µF 16 V Axial 8316221
C101, C130, C167 10 µF 16 V Axial 8316101
C115 100 µF 16 V Axial 8317101
C109 2.2 µF 16 V Axial 8315221

The manual also lists added parts that are not on the schematic, including a 1000 pF capacitor in parallel with C28 and small capacitors at U16, R39, R40 and R47.[5]

Memory PLUS adapter

[edit | edit source]

Tandy's Memory PLUS expansion adapter (PCB 8859004) has four 10 µF 16 V axial electrolytics, C9, C14, C17 and C20.[6]

Option boards in the EX manual

[edit | edit source]
Polarised capacitors on option boards
Board Ref Part Source
RS-232 interface board, 25-1014 C11, C12 4.7 µF 50 V axial electrolytic Parts list, PDF p. 164
RS-232 interface board, 25-1014 C13 10 µF 25 V axial electrolytic Parts list, PDF p. 164
Mouse controller/calendar, 25-1015 C10, C16, C20, C21 33 µF 6.3 V radial tantalum Parts list, PDF p. 211
PLUS Network 4 interface C102, C105 33 µF 10 V radial tantalum Parts list, PDF p. 225

The mouse controller/calendar board also carries a 3.0 V CR2320 lithium coin cell (Radio Shack 23-163), for which Tandy gave a life of one year.[7] Remove an old cell before it leaks; see Battery Explosion, Capacitor or Corrosion Damage.

Replacement procedure

[edit | edit source]
  1. Unplug the machine, remove the supply board, and discharge and measure the reservoir capacitor before touching the board.
  2. Photograph the board and note the polarity of every electrolytic.
  3. Replace the capacitors one at a time, matching capacitance and at least the original voltage rating. Use 105 °C low-ESR parts on the secondary side.
  4. Test the supply on a load before refitting it. Tandy's minimum test load is 1.25 A on +5 V (4 ohms, 20 W) and 0.1 A on +12 V (120 ohms, 3 W), and the manual warns that the supply must never run without a load.[3]
  5. Check the outputs against the limits in General Maintenance.
[edit | edit source]

References

[edit | edit source]
  1. ↑ Tandy Corporation, Tandy 1000 EX Technical Reference Manual, catalogue no. 25-1510, 1986, hosted as File:Tandy 1000 EX Technical Reference Manual (25-1510, 1986).pdf.
  2. ↑ "Tandy 1000 EX motherboard short", Vintage Computer Federation forum, January 2019, thread. Post by bitcom, 24 January 2019.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Tandy 1000 EX Technical Reference Manual (25-1510), 28 W single-input supply 8790083 (PDF pp. 89-107) and dual-input supply 8790086 (PDF pp. 108-126): troubleshooting caution, parts lists, schematics 3P-M1-0163 and 3P-M1-0159.
  4. ↑ Tandy 1000 EX Technical Reference Manual (25-1510), T1000 EX Main Logic Subassembly 8859000 parts list, PDF pp. 71-74.
  5. ↑ Tandy 1000 EX Technical Reference Manual (25-1510), "Main Logic Schematic Cuts, Jumpers and Additional Parts", PDF p. 75.
  6. ↑ Tandy 1000 EX Technical Reference Manual (25-1510), "Memory PLUS Expansion Adapter" parts list, PDF p. 144.
  7. ↑ Tandy 1000 EX Technical Reference Manual (25-1510), RS-232 Interface Board parts lists (PDF pp. 164-165), Mouse Controller/Calendar specifications and parts list (PDF pp. 190 and 211), PLUS Network 4 Interface parts list (PDF pp. 225-226).


Retrieved from "https://retrotechwiki.com/index.php?title=Tandy_1000_EX_Capacitor_Replacement_Guide&oldid=29577"