Power Designs 6050D Power Supply Repair

Bringing a Power Designs Inc. 6050D Universal DC Source back to life.

Ebay Power Designs 6050D power supply
Ebay Power Designs 6050D pow­er sup­ply buy it now pho­to


The Power Designs Inc. 6050D is the D vari­ant and 5th in the series of 6050 pow­er sup­plies. It is a lin­ear pow­er sup­ply designed to out­put 0 to 60 volts DC in 4 decreas­ing amper­age ranges from 5 to 1 amps as the volt­age is increased. It uses the Power Designs UNIPLY® design (Patent #3,699,352) to accom­plish this.
Here is the infor­ma­tion from the 1997 web­site.

What is it?

Uniply offers a wide range of volt­age and cur­rent in a sin­gle out­put bench pow­er sup­ply. It pro­vides fea­tures not avail­able with com­mon dis­s­ap­a­tive cir­cuits. Because of its unique design, it’s like hav­ing a fam­i­ly of pow­er sup­plies at your fin­ger­tips. Uniply is offered in both con­stant volt­age and con­stant voltage/constant cur­rent mod­els. Simply stat­ed, it’s a wide range con­stant pow­er source.

What does it do?

By pro­vid­ing high­er cur­rent at low volt­ages and high­er volt­age at low­er cur­rents, Uniply allows max­i­mum flex­i­bil­i­ty in a sin­gle pow­er sup­ply. No longer is it nec­es­sary to have a vari­ety of pow­er sup­plies avail­able for dif­fer­ent pur­pos­es. A sin­gle unit replaces a mul­ti­tude of pow­er sup­plies.

How does it work?

To make life eas­i­er, the pow­er sup­ply is divid­ed into sev­er­al dis­tinct ranges. Each range has its own DC pow­er source which is auto­mat­i­cal­ly select­ed accord­ing to the out­put volt­age and cur­rent require­ments. When the cur­rent attempts to exceed the max­i­mum lev­el for a giv­en range, an LED lights. When the out­put volt­age lev­el is reduced or increased, the appro­pri­ate cur­rent range will be auto­mat­i­cal­ly select­ed. There are no man­u­al switch­es used to change ranges.

The pow­er sup­ply was pur­chased on Ebay, in “for parts or not work­ing” con­di­tion. It looked pret­ty rough with a miss­ing volt­age con­trol, and pow­er switch loose inside the case.

Ebay picture of the Power Designs 6050D with cover removed
Ebay pic­ture of the Power Designs 6050D with cov­er removed

One of the first projects for this pow­er sup­ply was an exten­sive clean­ing and inspec­tion. After look­ing at the con­di­tion of the elec­trolyt­ic capac­i­tors, I decid­ed that a full re-cap would be a wise choice. All elec­trolyt­ic capac­i­tors were replaced with Nichicon capac­i­tors.

PD 6050D circuit board cleaning. About 1/2 done
PD 6050D cir­cuit board clean­ing. About 1/2 done
PD6050D capacitor / rectifier board with new Nichicon capacitors
PD6050D capac­i­tor / rec­ti­fi­er board with new Nichicon capac­i­tors

After replac­ing the miss­ing volt­age con­trol poten­tiome­ter with a VRN 84048 series 10-turn 10 K pot, remount­ing the pow­er switch, and sev­er­al quick checks for shorts, it was time to pow­er up the unit.

All inter­nal volt­ages checked out good, includ­ing the 4 addi­tive sup­plies for the UNIPLY® elec­tron­i­cal­ly con­trolled vari­able imped­ance sec­tion. I was able to set a volt­age that was rock steady under load, but could not adjust the cur­rent con­trol for set­ting the con­stant cur­rent mode lim­it. There was also a prob­lem with the front pan­el dis­play when switch­ing to the amps dis­play.

The 2K ohm cur­rent con­trol poten­tiome­ter end­ed up hav­ing an open resis­tance cir­cuit, and the replace­ment is a Vishay Spectrol 534 series 10-turn 2 watt unit. The dis­play switch was a sealed unit with inter­mit­tent con­tacts, and was replaced with a C&K 7000 series DPDT On-On  unit. The dis­play now workes prop­er­ly, but still no cur­rent con­trol.

PD6050D 7segment display board back
PD6050D 7segment dis­play board back
PD6050D top viewl from back of power supply
PD6050D top view from back of pow­er sup­ply

After many hours of trou­bleshoot­ing, the prob­lem with the cur­rent con­trol end­ed up being a faulty tran­sis­tor Q11, a NPN  2N2205A in a TO-18 Case. I did end up adding some slip-on heatsinks for some of the warmer tran­sis­tors.

PD6050D-4 Rev A board Top
PD6050D‑4 Rev A board Top
PD6050D-4 Rev A board Top backlight traces
PD6050D‑4 Rev A board Top back-light traces
PD6050D output Connector Board
PD6050D out­put Connector Board
PD6050D power transistors heatsink
PD6050D pow­er tran­sis­tors heatsink
PD6050D back side of heatsink
PD6050D back side of heatsink
PD6050D UNIPLY capacitor / rectifier Board 16 - 60 volt side
PD6050D UNIPLY capac­i­tor / rec­ti­fi­er Board 16 — 60 volt side.
PD6050D Top Viewl C8 before replacement
PD6050D View of capac­i­tor C8, mount­ed on the back side of the board and crow­bar SCR for over­volt­age pro­tec­tion.
PD6050D back panel
PD6050D back pan­el

The front pan­el and out­er case cleaned up sur­pris­ing­ly well using sev­er­al dif­fer­ent clean­ers. I used N‑Heptane for remov­ing stick­er residue from the anodized alu­minum pan­el and acrylic dis­play, and Novus 3, 2, and 1 for remov­ing the scratch­es and haze from the dis­play, LED, and AC indi­ca­tor.

PD6050D front panel Off
PD6050D front pan­el Off
PD6050D front panel On reading 24.1 volts, with temporary dial-a-pot for voltage control
PD6050D front pan­el On read­ing 24.1 volts, with tem­po­rary dial-a-pot for volt­age con­trol dur­ing load test­ing
Power Designs TW6050D Schematic
Power Designs TW6050D Schematic

Original spec­i­fi­ca­tions for this pow­er sup­ply were:
0.005%   volt­age reg­u­la­tion
0.02%      cur­rent reg­u­la­tion
1 mv P‑P  volt­age rip­ple-noise
5 ma P‑P cur­rent rip­ple-noise

Under full load at the upper volt­age in each of the 4 ranges, volt­age reg­u­la­tion was bet­ter than 0.002% and volt­age rip­ple-noise was less than 0.25 mv P‑P.

The PD6050D is cur­rent­ly my favorite lin­ear that I own, but I am cur­rent­ly work­ing on restor­ing it’s big­ger broth­er, the Power Designs 6150. It is a mas­sive unit capa­ble of 15 amps out­put on it’s low­er range.  I am search­ing for a PD6150 schemat­ic if any­one has one avail­able.
FOUND — See the PD6150 project post

4 Replies to “Power Designs 6050D Power Supply Repair”

  1. I, too, have a Power Designs 6150 in need of repair. Consequently, I am also search­ing for a schemat­ic for this sup­ply. Have you locat­ed one and if so, could you send me a pdf of it?

    1. Edward,
      Still no leads on a schemat­ic, so I am still look­ing. I am cur­rent­ly inter­est­ed in dis­cov­er­ing which trim­mer pot adjusts the cur­rent cal­i­bra­tion for the front meter.

      Greg (Barbouri)

  2. I see you have the 6050D schemat­ic. Do you have a copy of the man­u­al handy?

    I have a 5150D that is quite sim­i­lar and can’t find a man­u­al or schemat­ic.

    1. Here is an exter­nal link to the dual TW6050D schemat­ic:
      TW6050D PDF

      Is the 5150D a full width rack mount unit, or sim­i­lar in size to the 6050D ?
      The 6150 is a full width rack unit and has sim­i­lar specs to your 5150D and its man­u­al is locat­ed at the end of this blog post.

      Greg (Barbouri)

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