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

16 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)

  3. Hi Greg, nice to find a fel­low Power Designs enthu­si­ast. I too have a fond­ness for my 6050 col­lec­tion. Although my col­lec­tion can­not rival yours, I still have enough to pet every day. I cur­rent­ly have the 6050A, 6050C and 6050D. I decid­ed to do some upgrad­ing to my 6050C and while search­ing for a schemat­ic I came across your web site. I was blown away at the upgrad­ed 6050C pan­el meter that I want­ed to do so I decid­ed to just order your boards from OSH Park and put it to work. My it is very accu­rate indeed. 

    Now my enthu­si­asm has increased and I am now in the final design stages of a drop in direct DPM replace­ment for the 6050D. It is all based on your 6050C design. The new board how­ev­er will be slight­ly larg­er, about 3/8″ extend­ed at the edge con­nec­tor end to accom­mo­date for all parts need­ed. The board will fit to the exist­ing plas­tic hous­ing and have 4 dig­it res­o­lu­tion as your 6050C design. The far left dig­it dis­play for volts/current indi­ca­tion will be used as 4th dig­it so for volt/current indi­ca­tion, two LED bars will be just below the seg­ment dis­plays for visu­als, one for volts and the oth­er for current. 

    I will post notice of my final build here and hope to have it on my web site soon. FYI, my site is not up just yet.

    Thanks for your inspiration


  4. I just uploaded my files to OSK Park today. My first design was to incor­po­rate every­thing onto one board and by extend­ing the edge con­nec­tor down by an addi­tion­al 3/8″ which was the max that I could go and still have enough clear­ance above the Overvoltage pot on the front pan­el. Things just got way too tight so I decid­ed to scrap that and went with the pig­gy­back design sim­i­lar to what you did for the 6050C meter. I have a PDF with the schemat­ics and OSH Park board lay­out images. Currently my web­site is down and not able to upload the PDF and will mes­sage soon to advise when it is avail­able for download.


    1. Hey Ron and Barbouri,
      Thanks for your great arti­cles and upgrades! I just bought a 6050C
      and was look­ing for a schematic.

      1. Hi Mick,
        I have only been able to find man­u­als for the 6050_ A, B, and D.
        The 6050B man­u­al should be very sim­i­lar to the 6050C and uses the same display.

        Greg (Barbouri)

        1. Thanks Barbouri, I found the schemat­ics and parts list on EEVBlog for the 6050B! Will see what is next. On my 6050C, (start­ing with both pots at zero) the con­stant cur­rent seems to work once i twist the cur­rent pot about 3 turns to the right (It flips over to con­stant volt­age once i do this) and it seems very acc­cu­rate when mea­sured. The cur­rent how­ev­er, nev­er ris­es above 0.00 no mat­ter what I do, and it is hit or miss to even get it into con­stant cur­rent mode.

          I will see if I can trou­bleshoot the pot, and test com­po­nents to see whats up, but if you have any thoughts let me know.

  5. Just want­ed to add/suggest, see­ing as you have worked on these quite a bit, maybe a ‘Troubleshooting Power Designs Power Supplies’ arti­cle with some steps as to com­mon fail­ure modes and links to your oth­er posts would be a good way to pull togeth­er all of the knowl­edge you gained repair­ing these! I know I would read it.

    FWIW, pics of my unit are @ https://www.eevblog.com/forum/testgear/looking-for-goodinexpensive-bench-power-supply/msg3085785/#msg3085785

    1. Hi Ron,
      I just ordered a set of your boards from OSH Park.
      I have been work­ing on a Power Designs 6010D which uses the same dis­play mod­ule as the 6050D.
      The orig­i­nal dis­play mod­ule has had a rough life and isn’t very lin­ear in its read­ings, so hope­ful­ly this will be a nice upgrade for this unit.

      Thanks for design­ing the board.
      Greg (Barbouri)

  6. I have a PD 3650S pow­er sup­ply that isn’t work­ing prop­er­ly. To accu­rate­ly describe it’s behav­ior is dif­fi­cult because it isn’t con­sis­tent. I have found schemat­ics (http://ftb.ko4bb.com/manuals/
    which includes many test points and volt­age read­ings. Would you be will­ing to let me send you video dis­play­ing the behav­ior in the hope you could help me iden­ti­fy what sec­tion to con­cen­trate on?


    1. Hi Barrett,
      The 3650S is a Floating Output pow­er sup­ply with an auto­trans­former pre-reg­u­la­tor. I have no expe­ri­ence with this type of Power Designs supply.
      There has been some dis­cus­sion of this sup­ply on the EEVblog, so you may be able to find some­thing there that will help.
      Typically on these old­er sup­plies the elec­trolyt­ic capac­i­tors are the first sus­pects, and then meter switch­es and poten­tiome­ters with dirty contacts.

      Greg (Barbouri)

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