[time-nuts] Re: HP z3816a DC power supply DIP switches

[ed breya]

That's quite a bit different from the PS in the Z3801A.

 From the pictures, I'd guess that the "A" and "B" markings on the DIP 
switch are for 24 or 48 V AC or DC Battery operation. I did a little 
looking around, and found this:

http://www.realhamradio.com/GPS_Z3816A_Receiver.htm

It says that it supposedly can run on 120 VAC, but the circuitry on your 
board doesn't look like it can support it as is. If you blow up the 
little picture of the back panel on the website, it sure looks like a 
standard IEC line power cord is plugged in, but the text is illegible. 
If you investigate more, you may find the official specs and appearance.

The empty space on the PS board looks like it can possibly fit a small 
AC SMPS circuit, but the layout is not appropriate for line voltage - 
the clearances are way too small for it to be proper, safety-wise. This 
means that it probably is not where line power would go, and the only 
other place might be in the main power section, over by the big cap. The 
problem with this scenario is that cap is way big in C (2200 uF), and 
way short on voltage rating (100 V) for line input. It could be that 
there was a line voltage option, that entailed using some different 
parts in the main section, plus maybe some things to fill up the empty 
zone. Instead of having anything to do with line power, that space may 
be for a 12 V option. There is a "12" spot on the DIP switch, and some 
text on the board about power ratings with the different voltages.

Another possibility is that a transformer could could go in, to run from 
line voltage to make low AC - 24 or 48 Vrms. But, it would need to be in 
the 50-100 VA size range, kind of big to squeeze into the cabinet. Look 
at the mechanical features of the cabinet to see if there are extra 
holes and such to mount more stuff in there.

Anyway, as it appears to me, the DIP switch sets up the power control 
functions such as UVLO, OVLO (or OVP crowbar), and maybe power-on/reset 
signalling, depending on the power source type and nominal voltage. One 
thing to double check is how much polarity matters. If it can run on low 
voltage AC already, then it probably has a bridge rectifier input, so it 
won't care about the DC polarity. If it really is for DC-only, then 
there's probably a blocking rectifier for RVP, or less likely a shunt 
rectifier that will blow the input fuse for RVP. A little inspection and 
reverse engineering will tell you what the deal is.

It should self-protect, so you can try setting it for "24B," and put in 
24 VDC from a supply. Don't forget about the negative input R that will 
make it draw more current at lower input voltages - the supply has to 
put out enough current to handle it, once the input voltage gets high 
enough that it decides to turn on. It looks like this model takes way 
less juice than say, the Z3801A, but the same tendency will be there.

Ed