Tandy 1000 HX Capacitor Replacement Guide
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No HX service manual or parts list has been found, so the capacitor values for the Tandy 1000 HX power supply come from the Tandy 1000 EX technical reference manual. The HX supply in the photograph carries the transformer (TO-4349) and the part references of the EX's 28 W single-input supply 8790083.[1][2] One owner ran his HX on his EX's supply, and an open hardware replacement board is designed to fit both machines.[3][4] Read the values on your own board before ordering. See Capacitor Failure Symptoms for the signs of a failing part.
 | The supply rectifies the mains directly into its 200 V reservoir capacitor. Unplug the machine, wait, and measure across the reservoir before working on the board. |
Power supply
[edit | edit source]Values for supply 8790083, from the EX manual:[1]
| Ref | Capacitance | Rating | Position |
|---|---|---|---|
| C4 | 220 µF | 200 V | Primary reservoir |
| 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 dual-input version 8790086 numbers its capacitors differently; its list is on Tandy 1000 EX Capacitor Replacement Guide. C1 and C2 are 0.1 µF 250 V AC film capacitors across the mains; replace them only with X-class safety capacitors.[1]
Main logic board
[edit | edit source]No parts list for the HX main board has been found. Record the value, voltage and polarity of each electrolytic before removing it. For comparison, the EX main board has twelve axial electrolytics, all 16 V: seven 22 µF, three 10 µF, one 100 µF and one 2.2 µF.[5] The HX board is laid out differently: its sound chip is at U19, where the EX's is at U15.[6][5] Do not order from the EX list without checking.
One owner replaced the audio output stage capacitors on an HX while chasing speaker noise; the noise came from the sound chip, not the capacitors.[6]
Memory card
[edit | edit source]The HX takes the same PLUS memory card as the EX.[7] Tandy's Memory PLUS expansion adapter has four 10 µF 16 V axial electrolytics, C9, C14, C17 and C20.[8]
Replacement procedure
[edit | edit source]- Unplug the machine, remove the supply board, and discharge and measure the reservoir capacitor.
- Photograph the board and compare the values printed on the capacitors with the table above.
- 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.
- Test the supply on a load before refitting it: at least 1.25 A on +5 V and 0.1 A on +12 V, as in Tandy's EX procedure. Never run it without a load.[1]
- Check the outputs against the limits in General Maintenance.
Related pages
[edit | edit source]- Tandy 1000 HX
- Tandy 1000 HX General Maintenance
- Tandy 1000 HX Troubleshooting Guide
- Tandy 1000 EX Capacitor Replacement Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 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. Parts list for switching power supply unit 8790083 (T1: TO-4349), PDF pp. 102-104; schematic 3P-M1-0163, PDF p. 107.
- ↑ Blake Patterson, photograph of a Tandy 1000 HX power supply board, 2019, CC BY 2.0.
- ↑ "Tandy 1000 HX noisy speaker with idle screen", Vintage Computer Federation forum, February 2025, thread. Post by Hamsterbasher, 4 February 2025.
- ↑ tgotright, "Tandy1000EX-HX-ATX", GitHub repository, 2021: "Drop in replacement Power Supply board for Tandy 1000 EX and HX computers" (retrieved 2026-10-22).
- ↑ 5.0 5.1 Tandy 1000 EX Technical Reference Manual (25-1510), T1000 EX Main Logic Subassembly 8859000 parts list, PDF pp. 71-74.
- ↑ 6.0 6.1 "Tandy 1000 HX noisy speaker with idle screen", Vintage Computer Federation forum. Posts by Hamsterbasher, 1, 7 and 22 February 2025.
- ↑ Jeff Hayes, "Tandy 1000-series FAQ", version 2.52, 25 October 2005, TVDog's Tandy 1000 archive (retrieved 2026-10-21). Sections II.A.1 and II.I.1.
- ↑ Tandy 1000 EX Technical Reference Manual (25-1510), "Memory PLUS Expansion Adapter" parts list, PDF p. 144.