Navigation

 

     Contact Details

     Peter Miles
     Northam, Western Australia
     QRZ Page: VK6YSF

 

     Email

     

 

       Social Media

             

 

 

35AMP POWER SUPPLY REPAIR

35A power supply repair. 24 January 2025.


 

A recently purchased 35-amp power supply, lacking any manufacturing markings, appears to be commercially constructed and resembles the Motorola 10Amp HPN1007A unit in both design and consistency with the schematic, however this power supply has six 2N3055 power transistors and there are variations to the regulation board. 

The power supply functioned well for approximately a year before the mains fuse operated, accompanied by a brief growling hum from the transformer under load. The fuse appeared to have blown due to a very high fault current, which completely vaporized the element inside the glass fuse—a clear indication of a short circuit within the power supply.  

 

  Photo 1. Top front view of the power supply.

 

  Photo 2. Rear view of the power supply showing the six 2N3055 power transistors

 .

 Photo 3. Transformer spec plate.  Photo 4. Blown 240 VAC 8A fuse.

 

  Photo 5. Power supply regulation board (shown within the broken line in the circuit schematic) .

 

  Figure 1. Circuit schematic of a Motorola HPN1007A power supply.

 

To isolate the fault and verify that the transformer was not faulty, the secondary connections to the transformer were disconnected, thereby isolating the AC circuits, including the transformer, from the DC circuits. The mains supply was then connected, resulting in the fuse remaining intact. A healthy 37 VAC was measured across the transformer’s secondary windings, confirming that the transformer was operating normally and that the fault was within the DC section of the power supply.

The two rectifier diodes D1 and D2 were tested, revealing that D2 was short-circuited, creating a hard half-cycle short with D1.
Both diodes are to be replaced with VS-70HF10 diodes, rated at 100V and 70A, as the existing diodes appear to be automotive button diodes of indeterminate specifications.

 

  Photo 6. Original diode attachment to the heat-sink.

 

Photo 7. Button diode mounting    Photo 8. Button diode location on the heat-sink.

 

The VS-70HF10 is a standard recovery rectifier diode manufactured by Vishay. It is designed for high-current applications and will be more than adequate for the job based of the following specifications:

  • Maximum Repetitive Reverse Voltage: 100 V

  • Average Forward Current: 70 A

  • Forward Voltage: 1.35 V at 220 A

  • Maximum Surge Current: 1.25 kA

  • Package Type: DO-203AB (DO-5), stud mount

  • Operating Junction Temperature Range: -65°C to 180°C

 

The VS-70HF10 rectifier diodes come in several variants, with the device code and specifications highlighted in blue, as per the one used in this repair. An important variant is that the device can be supplied with reverse polarization, and as noted in reference 4 in the table, this particular device has the cathode connected to the stud.

 

1 Vishay Semiconductors product
2

70 = standard device

71 = not isolated lead

72 = isolated lead with silicone sleeve

(red = reverse polarity)

(blue = normal polarity)

3 HF = standard diode
4

None = stud normal polarity (cathode to stud)

R = stud reverse polarity (anode to stud)

5 Voltage code x 10 = VRRM (see Voltage Ratings table in spec sheet) 10 = 100V
6

None = stud base DO-5 (DO-203AB) 1/4" 28UNF-2A

M = stud base DO-5 (DO-203AB) M6 x 1

 

Figure 2. VS-70HF10 rectifier diode dimensions.  Photo 8. VS-70HF10 rectifier diode

  

The button diode arrangement was easily replaced with the new VS-70HF10 rectifier diode by drilling out the existing heat sink holes to 6mm and mounting the new rectifier diodes. In this arrangement, the heat sink is at a positive DC voltage and is mounted with insulating feet. See photo 9.

  

  Photo 9. New VS-70HF10 diodes fitted to the heat-sink.

 

Photo 10. VS-70HF10 diodes connected to the transformer secondary winding. Photo 11. Power supply output voltage under load.

 

With the new rectifier diodes installed, the power supply was switched on, and the output voltage was measured with about 10A of load, showing 13.66VDC at the output terminals.

 

VS-70HF10 diode data sheet: https://www.vishay.com/docs/93521/vs-70hfrseries.pdf  

 

TOP OF PAGE

 

Page initiated 24 January, 2025

Page last revised 1 February, 2025

 

 

   Space Weather

   Solar X-Rays

   Geomag Field

   https://www.swpc.noaa.gov/

    

   Notice Board

VK6YSF JS8Call and Olivia 8/250 operations.

Current activity is generally, however not restricted to operations with JS8Call and Olivia 8/250 on the 20m and 40m band.

Proposed band and mode activity is often communicated on HamSpots: https://hamspots.net/js8/ or my profile on 

X: https://x.com/vk6ysf97230 .

Feel free to contact me to discuss or arrange a schedule for a contact.

 

VK6MJM LF (136 kHz) and MF (474 kHz) Beacon

VK6MJM is a  LF/MF station located in Manjimup, Western Australia.

Mode: Mode: FST4W 300 (Similar to WSPR)

Station details were presented by Peter Hall (VK6HP) at PerthTech 2024.Presentation PDF: Peter Hall VK6HP at PerthTech

QRZ Page: VK6MJM on QRZ.com

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

All content may be used for unlimited distribution with full credits.

Amateur Radio Station VK6YSF - Promoting amateur radio communication and experimentation.