[time-nuts] Re: Need help to DATUM Power Supply MPS (Type MFS Modular Frequency Systems)

[Wilko Bulte]

The attached PDF shows which voltages are used in a desktop variant. 

20.5VDC is noted here. And a separate heater supply. 

Hope this is of use to the OP. 

Wilko



> On 10 Jun 2022, at 01:49, ed breya via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Yes, that transformer sure looks burned out. It's hard to tell how big it is from the pictures, but my impression is that it looks kind of skimpy to run a FRK Rb plus whatever else is going on like a GPS RX and uP system, and maybe battery charging too. You can easily estimate the VA rating by measuring the dimensions and comparing to standard transformer frame sizes. Generally, the VA rating should be at least twice the total raw (not the regulated output values) DC power produced, with conventional rectification and filtering. This can be exceeded for a while, say during warmup of the Rb, as long as it goes back to normal in a reasonable amount of time. It's mostly about temperature rise - if you have good cooling, you can get more out of it.
> 
> Transformers are pretty tough, so having one burn out in normal service calls for some investigation of why it happened, before you risk taking out a replacement too.
> 
> Regardless of the VA rating that should be used, you're probably stuck with using the same size and style as the original, just to fit it mechanically. If it's plenty big enough VA-wise, then all's well. If it's marginal, you can at least add enhanced protection to avoid another burnout.
> 
> Regarding DC supply voltages, the main one will be something around 24 V for the Rb. I would guess that the DC-DC converter on the supply board makes +5 V (or 3.3 or whatever) for the brain and GPS RX, and the 78M12 makes +12 V for the analog, and that there are no negative supplies - unless there's more to the supply system that's not shown. Since external 24 VDC can supposedly run the whole thing, I don't think you'd have to worry about making any of the voltages from the AC transformer except for the 24 V, even though it appears to have a multi-tapped winding. I didn't see anything in the OP about whether the thing works with just external DC, so this should be confirmed.
> 
> There's a lot more circuitry on the board than seems necessary just for power, so it may be worthwhile to reverse engineer it a bit - especially the four big transistors and U3 and U4, which looks like two identical functions of some sort. Maybe extra voltage regulation, or maybe 1 PPS amplifiers?
> 
> Once you do figure everything out and get a fresh transformer, note that the original is banded to reduce magnetic emission. It appears to have both the copper strip around the bobbin zone, and the steel (or sometimes mu-metal) band around the core, but not the third thing commonly done, which is insulating the core mounting. It will function without these, but may interfere with the Rb unit, especially if it's nearby. You won't find these features in run of the mill OEM replacement transformers, so you'd have to specify them, or add them yourself. If you get a transformer with same dimensions as original, you can transplant these pieces from the old one.
> 
> Ed
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