Power Designs TP330 Power Supply

I decid­ed to take a gam­ble on pur­chas­ing a Power Designs Inc. TP330 triple out­put pow­er sup­ply. It was a bit rough look­ing with a bunch of stick­ers on the front pan­el, but no scrape marks from past stick­er removal vis­i­ble. The sell­er stat­ed that the bot­tom ana­log meter was non-func­tion­al, but the out­put ter­mi­nals mea­sured volt­age that changed with the volt­age knob.

Power Designs TP330 pow­er sup­ply as received

I was hop­ing that the non-work­ing meter was a bad switch or some­thing sim­ple. Oh-Well noth­ing ven­tured, noth­ing gained.
The Power Designs PS330 has two 0 to 32 volt out­puts rat­ed at 1 Amp that can be oper­at­ed sep­a­rate­ly, or in track­ing mode where source A is con­trolled and tracks the out­put of source B. The third out­put is a 0 to 15 Volt at 2.5 Amp non-track­ing sup­ply.
All the out­puts have a recessed cur­rent lim­it poten­tiome­ter along with an over­volt­age trip set­ting poten­tiome­ter and fault indi­ca­tor
The pow­er sup­ply arrived in good con­di­tion and was well packed con­sid­er­ing it’s size. My first step was to open it up. The out­er case is held on with 5 slot­ted screws, one in the rear and four in the front corners.

Power Designs TP330 case removed for inspection

Other than being a bit dusty and dirty, the pow­er sup­ply checked out good. All the fus­es were the cor­rect val­ue, no vis­i­bly dam­aged com­po­nents, and all the elec­trolyt­ic capac­i­tors mea­sured val­ues were good enough for fur­ther test­ing.
Since I real­ly dis­like work­ing on dirty equip­ment, the sup­ply was tak­en out­side for an ini­tial clean­ing with com­pressed air.
Now that the unit was a bit clean­er, it was time to pow­er it up and take a look at the non-func­tion­ing meter.
The meter was not mov­ing at all with changes in the low­er 15 volt out­put. I could also see that the meter nee­dle was rest­ing against the dial face, which would def­i­nite­ly keep it from work­ing prop­er­ly. There was also a vary­ing small volt­age on the meter ter­mi­nals that cor­re­spond­ed to the out­put ter­mi­nal volt­age changes. So it was time to remove and open up the meter.

Jewell / Modutec W‑Series ana­log meter repaired

All the meters on the TP300 are Jewell / Modutec W‑Series which are a rear mount­ed style that mount flush with the front pan­el. These meters use a taut-band move­ment sup­port­ed on each end with a flat spring.
The spring on the front of the meter move­ment had bro­ken its glue bond to the front adjust­ment sup­port which allowed the back spring to force the nee­dle against the dial plate. A small amount of 5 minute two-part epoxy allowed me to reat­tach the spring while I kept it under ten­sion until the epoxy cured. The meter was now work­ing again and was rein­stalled in the sup­ply for testing.

Power Designs TP300 load test­ing on all outputs

After load test­ing the sup­ply, source B and C showed around 0.042 mV of rip­ple on their out­puts while source A was around 0.1 mV of rip­ple. Source A and B under the same load­ing should have near­ly equal amounts of rip­ple, which even though is still real­ly low, made me think that the 45 year old capac­i­tors on the source A chan­nel need­ed to be replaced. Which also led me to believe that the rest of the capac­i­tors may not be too far behind. Another decid­ing fac­tor for replac­ing all of the elec­trolyt­ic capac­i­tors is that it is becom­ing hard­er and more expen­sive to find qual­i­ty axi­al style capac­i­tor replace­ments recent­ly, and in 10 years who knows what the avail­abil­i­ty will be.

Power Designs TP330 par­tial elec­trolyt­ic capac­i­tor replacement

I had most of the capac­i­tors in spares, but need­ed to order some oth­ers and the large chas­sis mount­ed 20,000 uF capac­i­tor for the source C, 15V sup­ply out­put.
While wait­ing for the capac­i­tor order to arrive I decid­ed to look at the dif­fer­ences of the TP330 and TP325 pow­er sup­ply mod­els.
The only schemat­ics that I have been able to find were for the TP325 mod­el. But when look­ing at the schemat­ic draw­ing title block, I noticed that some of the schemat­ic draw­ings were des­ig­nat­ed for TP325 / TP330 mod­els.
The TP325 mod­el has the same spec­i­fi­ca­tions for source A and B chan­nels, but the source C out­put is rat­ed as 0 to 6 volts and 0 to 5 amps, while the TP330 has a source C rat­ing of 0 to 15 volts and 0 to 2.5 amps.

TP330 source C 0–15V con­trol board

The source C con­trol board in the TP330 has a part num­ber of PS-TP325‑8 REV B which lead me to believe that the same board is used for both mod­els with a change of adjust­ments or components.

Source C con­trol board val­ue changes between TP325 and TP330

I checked all the pas­sive com­po­nent val­ues from the TP325 parts list against what was actu­al­ly pop­u­lat­ed on my TP330 board and found that 7 com­po­nent val­ues were dif­fer­ent. Also capac­i­tor C103 (20,000 uF) which is locat­ed on the chas­sis changed from 15 volts to 30 volts with the same capac­i­tance value.

TP330 side con­trol board for source A and B and out­put board

All of the out­put tran­sis­tors are the same for both mod­els which use TRW 1700 C TO‑3 case tran­sis­tors. Each of the source A and B chan­nels use two tran­sis­tors per chan­nel which are locat­ed on the rear heatsink. The source C chan­nel uses three tran­sis­tors mount­ed on left side met­al frame.

Power Designs TP330 rear heat sink and transistors
Power Designs TP330 rear heat sink resis­tors and wiring
Power Designs TP330 source C heat sink pan­el and transistors

The rest of the new capac­i­tors had arrived and were installed onto the sup­ply. All except the chas­sis mount capac­i­tor were replaced with long-life Vishay axi­al units and the chas­sis capac­i­tor was replaced with a 22,000 uF 50V Nichicon unit. I also decid­ed to check the Zener diode fil­ter­ing capac­i­tors which are in the volt­age ref­er­ence sec­tions of the source A and B board as these could also affect out­put noise on the chan­nels. The four Zener ref­er­ence capac­i­tors are 6.8 uF @ 35V her­met­i­cal­ly sealed Tantalum type units and when checked showed the cor­rect capac­i­tance, but had fair­ly high ESR val­ues.
I had some “New Old Stock” capac­i­tors that had ESR val­ues around 0.25 Ohms, where the TP330 capac­i­tors ranged from 1.2 to 4.7 Ohms, so I replaced them all.

Power Designs TP330 new elec­trolyt­ic capacitors

As I had men­tioned back in my HP 3314A Function Generator post, “I have nev­er seen a her­met­i­cal­ly sealed ver­sion of a Tantalum capac­i­tor fail”, well now I have… sort of?
The spec­i­fi­ca­tions for the TP330 are less than 1.0 mil­li­volt P‑P, and my mea­sure­ment for the source A chan­nel at full load was 0.1 mil­li­volt before the capac­i­tor replace­ment, which is well with­in spec­i­fi­ca­tions.
After the full capac­i­tor replace­ment source A dropped to 0.07 mV P‑P, source B at 0.014 mV P‑P, and source C at 0.028 mV P‑P all at full load.
Pretty impres­sive for a 45 year old pow­er sup­ply, but typ­i­cal­ly what I now expect for a well engi­neered Power Designs, Inc. pow­er supply.

Power Designs, Inc. TP330 triple-out­put pow­er sup­ply finished
Power Designs, Inc. TP330 pow­er sup­ply after clean­ing and repair

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