Lighthouse Electric Power Supply Project

Convert a Surplus PC SMPS To 6.3V DC Filament Supply

Shown in the picture below is the Voltek Corp. PC Switched Mode Power Supply. It measures only 9"L x 2"H x 1-3/8"H.
Input Voltage: 100-240VAC 1A 50-60Hz.
Output DC voltages before the conversion are: +5V @ 3.70A, +12V @ 600mA, -5V @ 50mA and +5V trickle voltage @ 100mA
It features an IEC power entry jack and remote ON/OFF.

Output Plug:
Orange +5V
Black = Common
Yellow +12V
Blue -5V
White = Remote ON/OFF
Grey +5V trickle

After the conversion, the output voltage will be 6.3V @ 3A. All other voltages remain unchanged.

Voltek PC PSU

Short description of PC SMPS Voltage Regulation
The error amplifier of the regulator IC compares the most powerful output voltage (Wattage), in this case our 5V output with a reference voltage (set value). If the output voltage is out-of range, the error amplifier adjusts the pulse width modulator to bring it back to set value. Our task is to lower the feedback voltage in order to fool the error amplifier, that the output voltage is to low. The circuit will compensate thus increasing the output voltage. It takes approximately only 15 minutes to make the conversion. One diode needs to be removed and one resistor replaced.

Conversion Procedure:
make sure, power is disconnected and capacitors discharged. Remove all mounting screws (4) from the enclosure and slide out the PCB as shown in the picture below. Remove D9 Zener diode and R7 resistor. Component locations are shown in the next picture. Replace old 820 Ohms R7 resistor with a new 1.2k resistor. D9 Zener diode was a 5.6V "Crow Bar" protection diode. In our application it is obsolete and need not to be installed.

Click on images to resize!
Cover Removed


WARNING POTENTIALLY LETHAL VOLTAGES MAY BE PRESENT!
Do not touch any part of the device with bare hands while under power. Filter capacitors may carry high voltage charge long after power was turned off. Wait until filter capacitors are discharged. Measure voltage with voltmeter to be sure. If you do not know how to handle high voltage circuits, do not handle this device. Get help from a qualified technician.

Calibration:
Connect a 8-12 Ohms 5W power load resistor to the PSU output, orange & black wires. Short the wht & grey (remote ON/OFF) wires with a jumper. Connect a DVM parallel to the load resistor. Switch the DVM to 20V DC range. Apply power. The DVM should indicate approximately 5.5V immediately. Adjust the output voltage with the VR1 trim-pot to 6.3V.

Component locations

This concludes the conversion. However, if you do not need the "Remote ON/OFF" feature, install an jumper between the white and grey wires. Solder it directly onto the PCB terminals. Other output voltages may be utilized for an power "ON" indicator LED (+5V), RIAA phono pre-amp (+12V), auto stand-by relay switch (+12V) and many other.
If this is an upgrade to an existing project, the IEC power input jack can be removed and the supply wires connected directly to your power switch and PCB as shown in Fig.1
Alternatively the IEC jack can be used as main power input. In that case the PSU top cover must be left off, the (L)ine wire un-soldered from the PCB and connected to the main power switch and routed back to the PSU L-Hot terminal as shown in Fig.2
Cooling:to operate the PSU safely and trouble free, adequate cooling must be provided. Mount it where plenty of air movement is present or attach it to a metal enclosure. Attach the side with the two screws (opposite of the label), which is the heat-sink side. Heat will dissipate through the whole enclosure.

This small PC power supply can be ordered online for $3.95 at Marlin P. Jones & Assoc. Inc.

Power Line connections

Line connections diagram

This small PC power supply can be ordered online for $3.95 at Marlin P. Jones & Assoc. Inc.

POWER SUPPLY PARTS
REF. # DESCRIPTION QUANTITY PART No: SUPPLIER
PSU Voltek Corp. Model: SPEC7188B 1 11687-PS www.mpja.com
R7 Resistor 1/4W 5% 1 1.2k any


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THESE PROJECTS ARE PROVIDED 'AS-IS', WITH NO WARRANTY OF ANY KIND.
USE OF THESE CIRCUITS SHALL BE ENTIRELY AT THE USER'S OWN RISK.
The publisher of this web site does NOT assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

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