I am missing a power supply and am looking for advice / pointers as to how to build a replacement. It outputs +12v -12v +5v at around 80W.
Not sure where to start… I’ve seen metalboxed PSUs with tabs for AC in, DC out online. But I need a C13 style plug also I guess so I’d need another box to mount that (?)
FWIW original looks like this:
Does it need to have the same physical dimensions? You can easily buy standard PC power supplies - and those output the voltages you want and come with a metal case and an IEC mains input socket. They’re Likely to have a higher capacity than 80W, but that shouldn’t matter, unless they’re physically too big.
You can search for ATX power supply. If you want to get from the standard multi-pin ATX connector to screw terminals, there are lots of cheap adapter boards available - search for “ATX power adapter board” - some of those even have LED displays built in to monitor the supplied voltages.
Nice. I want it to fit inside the display unit.
Its around 10cm x 8cm footprint, 25cm height.
You can kinda see how the original unit slots in there with the AC plug out the back (right side in photo).
ATX supply is going to be too large - dont they have some trickle circuitry for warm starting etc also(?)
Regarding the ‘trickle circuitry’: yes, the more modern supplies do have that, but it’s easy to wire a momentary contact push button to link two of the wires for ‘start’. You can also permanently connect them together if you don’t need the on/standby functionality.
Would something like this fit? Mini ATX PSU for small PC on Ali Express (about 18 US dollars at time of posting).
It’s 15cm x 8cm x 4cm. That one is rated 220V AC input: you might need to search for something similar if you need 115V AC input - I don’t know if that one would work on the lower input voltage, though some of them work on both supply voltages without having to set any switches.
You could also try one of the “MeanWell” power supplies that Jameco sells. Here’s one I used on a project last year: Amazon.com: Mean Well LRS-50-5 Switching Power Supply, Single Output, 5V, 10A, 50W, 3.9" L x 3.23" W x 1.18" H : Electronics
That one doesn’t have a 12v output, but they have a bunch of varieties, I believe some of them do.
I’d second using a MeanWell PSU … However … Last time I tried to buy one in the UK I had to prove that I was a bona-fide business to Mouser and Meanwell directly themselves.
I’ve no idea why … I am a bona-fide business in the UK, in the capacity as “sole trader”. This is recognised by HMRC, but not MeanWell, nor mouser.
I bought it from RS with no questions asked.
-Gordon
Great info all.
This PSU also taps out 220 AC to the display (see photo). The circuit diagram shows the tap coming after the suppression Caps and an inductor. I’m guessing I can find some place in these meanwell PSUs to do the same. (?)
Given the display PSU has X/Y caps anyway, perhaps just feeding 220VAC after the power SPDT switch would work too.
I found giving my VAT number was enough for Mouser.
I don’t know what I’m talking about, when it comes to PSUs, but I see the PicoPSU used for restoration projects. These are tiny circuitboards that take 12V DC input and deliver voltages in configurations for various retro computers.
(Notably, you’d have to find a separate solution for the 220V tab.)
E.g., see here: DC-DC ATX PSUs
or here: https://www.tindie.com/stores/dekunukem/
GitHub: GitHub - dekuNukem/PicoRC: PicoPSU adaptor for retro computers
https://www.mouser.com/ProductDetail/TDK-Lambda/MTW15-51212?qs=sGAEpiMZZMsPs3th5F8koGu8EUi%252BGg%252Brwdti8IzPR0Q%3D
The data sheet lists a whole bunch of models.
Cheers, This workstation needs around 100W from the PSU - but yes something like this.
I haven’t figured out how I’m going to generate the Display supply yet. I think it needs a tap from the 220VAC but also looks like it needs 70VAC (iff I’m reading the schematics right - which is a big if).
I’m also going to have to 3d print a case. All Tektronix equipment seem to have a penchant for having a really long plastic rod from the front panel power button to a latching power switch - so building something that holds the switch at the right angle to join up with the long plastic rod will be fun.
Had to smile as I recollected one of my very earliest tasks as an electrical apprentice - basically take this sheet of metal, these 50-60 “E” pieces of iron, these reels of wire, and make, yes make, a power supply transformer for an amplifier that “you will build” during next year as part of workshop practices training (RAF Locking, 1959), still have it lurking in collected scrap box. Of course the sensible answer(s) have been given by others, and impromptu answer would have been " find a scrap Desk-top computer where similar V’s were common " and lift the PSU from that - most have labels telling you wattage, current available. The intended target looked as though it had a cathode ray tube for the screen - which would need a EHT supply -not part of standard 12/12/5 PSUs but a simple standard cct - often driven by the line oscillator itself fed by the PSU - probably part of the display board tho cased for safety. In any case personal care advisable when working on/in such units as they are potentially lethal even after switching them off - the smoothing/step-up capacitor(s) and the tube can remain charged to dangerous levels for minutes or more. ATB.
Afterthought: Most faulty PSUs have a simple fault when they “stop”:
You probably have done but:
Great advice. Thx.
I have 1 computer+PSU that works, and an identical computer without PSU - hence asking about hacking together a replacement.
I’ve measured the tap to the CRT and it does appear to be 220vac going into another PSU next to the CRT - which I guess makes sense.
Nice constructor challenge - but the “find a comparable commercial unit - bought/scrap PC” advice is probably better. You might want to check the working PSU for in-use behaviour - such as phased start-up i.e. not all lines full power at switch on - preferably by feedback from other Retro’ers here or circuit diagram or handbooks - it is remarkable what is available on the Web about (old) products and how to fix them, failing that and with care, one can instrument the power-lines - if accessible - and you have a scope and/or voltmeters. Bear in mind that any phasing may be over in a few seconds or less so difficult to observe on simple test-equipment. Think of it as a bit like the boot-up phases on a lap-top where the boot-chip runs thro a check, then lights the screen, then runs up the disc for the OS to load; power units can include similar protective arrangements for itself or its working loads. Anyway - Good luck.
Your wise words make me realize I am waay out of my depth.
No idea whether the mains tap is actually something more complex and is multi phase etc.
This is the schematic. J1, pins 1,2,3 on left side is the mains ‘tap’. I see it goes thru an inductor - and if I skip that ??
Hi, Adam,
Wiser heads than mine have created this PSU: I have dissected the diagram - various parts are identifiable functions (the simpler ones…), and those occur in most PSUs. In keeping with most circuit diagrams the functionality starts on the left and generally ends on the right. This leads me to assume pins 1-3 are Line, Earth , neutral and just above is a switch for 230/115 V AC options. moving left at that level in the diagram is a standard 4 diode bridge rectification stage - plenty of chips can be used for this or 4 individual diodes (as per the diagram). The L-shaped part of circuitry above J1 is fed from Line and neutral and leads down to the out-going J1 via mains-noise filtering inductor L1.
Looking at the circuit to the RHS of the diagram, starting beyond the multiple windings transformer : The lower, 1/2 wave rectified -12V line feed straight through and to the fan. Above the Gnd line just above the -12V line is a complex block of circuitry - put simply it is a sensing circuit that monitors the input voltage (nominally 5V) and steers the A723 circuit which is voltage sensitive [protection kicks in at low/high limits. The A723 is described in great detail here:
Its function is to generate the +12V line (low current).
Last bit - the 4 transistors etc - it looks as though this monitors the overall unit as it is connected by T1 to all power lines and probably switches off the power feed Q5 T2. Obviously a full unit description may well contradict/confirm this analysis.
I can’t answer your Question about the inductor as there are good reasons to have a filter tho it wouldn’t stop the PSU functioning if omitted.
Finally - the absence of transistor/ other semiconductor product id’s, some component values, and the complexity of T1 make building a replacement PSU not a simple challenge - can providing the +/- 12V and 5V lines be achieved w/out the protective circuitry - probably Yes though it would be wise to ascertain load currents for each line from your working display,
If any Retro’rs can help Adam ( e.g. have an old spare PSU for his Tektronix display, or better details of the PSU design, I’m sure he would be grateful.), please do.
