VAXstation 3100 Power Supply Guide
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The VAXstation 3100 uses one of two switching power supplies, the H7821 in the smaller BA42-A box and the H7822 in the larger BA42-B box. DEC treated the supply as a single replaceable unit: its maintenance guide gives a check procedure, the output voltages at the system module and the removal steps, and no circuit or component information.[1][2] The repair information on capacitors comes from restorers.
Warning: the supplies rectify the mains onto capacitors rated 250 V and 400 V. Unplug the system box and confirm the capacitors are discharged before working on a supply board.[3]
Which supply
[edit | edit source]| Model | Enclosure | Supply |
|---|---|---|
| 30 | BA42-A | H7821 |
| 38 | BA42-A | H7821-00 |
| 76 | BA42-A | H7821-00 |
| 40 | BA42-B | H7822 |
| 48 | BA42-B | H7822-00 |
The same two supplies are used in the MicroVAX 3100, the DECstation 3100 and DECstation 2100, and DEC storage expansion boxes. The H7822-00 contains the H7821-00's board plus a second board.[3]
DEC's check
[edit | edit source]DEC's flowchart for a suspected supply fault:[2]
- Check that the wall outlet is live and that the power cord is plugged in.
- Switch on.
- If the green LED on the front of the system box does not light, replace the power supply.
- If it lights, measure the voltages at the system module power connector and the drive power connectors against the tables below.
The system unit adjusts itself to the mains voltage; there is no selector switch.[4][5]
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| Pin | Voltage | Tolerance |
|---|---|---|
| 1 | −12.1 V | ±5% |
| 2, 3, 4 | Ground | – |
| 5, 6, 8, 10 | +5.1 V | ±5% |
| 7 | +3.5 to +5.25 V | – |
| 9 | +12.1 V | ±5% |
| 11, 12 | Ground | – |
| 13 | −9 V, measured against pin 14 | ±5% |
| 14 | −9 V return (isolated supply) | – |
The −9 V output is isolated: measure it with the meter's negative lead on pin 14, not on chassis ground. The drive power connectors carry +12.1 V on pin 1 and +5.1 V on pin 4, with pins 2 and 3 grounded, both ±5%.[6]
If the LED is lit but the machine is dead or shows no video, use the FRU isolation procedure on VAXstation 3100 Troubleshooting Guide; DEC puts the power supply last, after the drives, MSC module, graphics module, memory and system module.[7]
Removing the supply
[edit | edit source]- Switch off and remove the system box cover (two screws; slide the cover forward and up).
- Remove the drive mounting panel (both panels on the Model 40).
- Disconnect the power cable from the system module.
- Remove the four screws holding the supply and lift it out.
- On the Model 40, move the two power cables from the old supply to the new one.
[8][9][10] DEC asks for a static wrist strap and mat when replacing FRUs.[11]
Capacitors
[edit | edit source]Malte Dehling reports that the VAXstation 3100 supplies suffer from leaking capacitors, and that most can be fixed by cleaning the board with isopropanol and replacing the capacitors. The boards carry no designators or polarity markings, so he numbered the positions himself and drew their locations.[3] In outline:
- The main board, common to both supplies, has five 1800 µF 25 V low-ESR capacitors (C1–C5), two 470 µF 250 V capacitors (C13, C14) and a further nine smaller electrolytics, two of them on small daughterboards.
- The H7822-00's second board adds a 220 µF 400 V capacitor (C20), four more 1800 µF 25 V low-ESR parts (C23–C26) and two smaller ones.
[3] The complete lists, with his position drawings and replacement notes, are on DECstation 3100 Capacitor Replacement Guide; storage and failure reports from MicroVAX 3100 owners are on MicroVAX 3100 Power Supply Service. Photograph each board and mark the polarity of every capacitor before removing any, and use low-ESR parts in the 1800 µF positions.[3] See Capacitor Failure Symptoms.
After a repair
[edit | edit source]Dehling finds that an H7821 or H7822 can be run on the bench without a load: the fans turn and the voltages are about right, but the LED does not light until some load is connected.[3] Refit the supply, check the rails against DEC's table above, and watch for a clean power-up countdown on the screen.[6][12]
Related pages
[edit | edit source]- VAXstation 3100
- VAXstation 3100 Maintenance Guide
- VAXstation 3100 Troubleshooting Guide
- VAXstation 3100 Documentation
- MicroVAX 3100 Power Supply Service
- DECstation 3100 Capacitor Replacement Guide
References
[edit | edit source]- ↑ 1.0 1.1 DEC, EK-285AA-MG-001, pp. 246 to 247, Appendix H. H7821 for the Model 30, H7822 for the Model 40.
- ↑ 2.0 2.1 DEC, EK-285AA-MG-001, p. 57, section 2.22 and Figure 2-17, power supply troubleshooting flowchart.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Malte Dehling, "DIGITAL VAXstation 3100 PSU Repair", GitHub repository README and drawings, github.com/mdehling/vs3100-psu-repair. Supplies by model, capacitor values and voltage ratings, repair and test notes. Community source.
- ↑ Digital Equipment Corporation, VAXstation 3100 Cover Letter, EK-393AA-CL-001, December 1989, p. 3 (File:VAXstation 3100 Cover Letter (EK-393AA-CL-001).pdf). The system unit adjusts itself to the correct voltage.
- ↑ Digital Equipment Corporation, VAXstation 3100 Model 40 Owner's Manual, EK-266AA-OM-001, January 1989, p. D-1, Table D-1 (File:VAXstation 3100 Model 40 Owner's Manual (EK-266AA-OM-001).pdf). Automatically adjusting AC input.
- ↑ 6.0 6.1 6.2 DEC, EK-285AA-MG-001, pp. 58 to 59, Figure 2-18 and Tables 2-15 and 2-16.
- ↑ DEC, EK-285AA-MG-001, pp. 244 to 245, section G.1. FRU isolation.
- ↑ DEC, EK-285AA-MG-001, pp. 91 to 92, section 4.2.1. System box cover.
- ↑ DEC, EK-285AA-MG-001, pp. 105 to 106, section 4.2.11 and Figure 4-22. Model 30 power supply removal.
- ↑ DEC, EK-285AA-MG-001, pp. 128 to 129, section 5.2.11. Model 40 power supply removal.
- ↑ DEC, EK-285AA-MG-001, p. 90, section 4.2. Static precautions.
- ↑ Digital Equipment Corporation, VAXstation 3100 Maintenance Guide, EK-285AA-MG-001, February 1989, pp. 3 to 5 (File:VAXstation 3100 Maintenance Guide (EK-285AA-MG-001).pdf). Power-up tests.