[time-nuts] HP5370 power supply measurements

[Rami Vainio]

Hello, I did SMPS mod to my 5370. If I remember correctly, consumption 
of +5V was ~5A and -5,2V ~7A. I removed original +5/-5,2V linear 
regulators and replaced them with step-down converters. -5,2V side I did 
float original diode bridge and capasitor and put smps module to 
positive rail. I also removed original prom card and put eprom directly 
to cpu card. Power consumption dropped to close 110W. There was no 
visible performance change after mod.


https://dl.dropboxusercontent.com/u/21770339/hp5370_ps_mod.JPG


Ramppa



-- 
      Rami Vainio    OH2LIY
      Email : rami.vainio at gmail.com
      Phone : +358 40 505 8085



On 11.7.2016 21:46, Poul-Henning Kamp wrote:
> Inspired by the recent thread about power trouble, I spent an hour
> to actually measure why the HP5370 gets so warm as it does.
>
> I'm running on 230VAC here, with the 230/240VAC power setting.
>
> With A6 and A7 removed and turned off: PAC= 4.2 W
>
> That is the loss in the transformer and rectifiers, since the "power"
> switch on the HP5370 really isn't that.
>
> Turning it on, PAC= 19.9W
>
> So the fan uses 15.7W.  (it's also noisy, I should find a replacement)
>
> I also measured the four unregulated DC voltages:
>
> 	-20V -> 28.9V
> 	-10V -> 13.4V
> 	+10V -> 13.4V
> 	+20V -> 28.9V
>
> Inserting A6 does not change the OFF state PAC measurably.
>
> Turning on however:  PAC = 140 W
>
> Voltages:
>
> 	-20V -> 27.5V
> 	-10V -> 10.9V
> 	+10V -> 11.9V
> 	+20V -> 27.1V
> 	+15V -> 14.99V
> 	-15V -> 15.04V
> 	+5V  -> 5.05V
> 	-5.2V-> 5.4V
> 	+10V -> 10.0009V
> 	-20V -> 123mV ripple
> 	-10V -> 2.02V ripple
> 	+10V -> 960mV ripple
> 	+20V -> 312mV ripple
>
> The unregulated busses are still waay over what the schematics
> would have you belive (10/20V).  The ripple on the -10V seems
> pretty high, but the four electrolytic capacitors seem healthy
> enough.
>
> Next I tried measuring the current on the four regulated voltages,
> which all have short-circuit measuring resistors:
>
> 	A6 pin  5- 6 188mV, 0.07R 3% -> 2.68A   +5V
> 	A6 pin  7- 8 498mV, 0.07R 3% -> 7.11A   -5.2V
> 	A6 pin  9-10 109mV, 0.4R  1% ->  .2725A +15V
> 	A6 pin 11-12  55mV, 0.4R  1% ->  .1375A -15V
>
> Since I measured this on the bottom of the motherboard, the contact
> and PCB trace resistance to/on A6 is also included so these currents
> are high estimates.
>
> Measuring with a clamp milliamp-meter instead I find:
>
> 	+5V   -> 2.2A
> 	-5.2V -> 5.5A
>
> Doing the math:
>
> 		 Brutto    Netto
> 	Trafo:    4.2 W    4.2 W
> 	Fan:     15.7 W   15.7 W
> 	OCXO:    14.0 W   14.0 W   Netto  Brutto
> 	-20:      3.8 W    2.1 W   2.1 W   3.8 W
> 	-10:     60.0 W   29.0 W  29.0 W  60.0 W
> 	+10:     31.9 W   13.4 W  13.4 W  31.9 W
> 	+20:      7.4 W    4.1 W   4.1 W   7.4 W
> 	----------------------------------------
> 		137.5 W   82.5 W  48.6 W 103.1 W
>
> Modern efficient DC/DC converters should therefore be able to
> reduce the PAC by about 50W or one third.
>
> I tried load-testing the unregulated busses, and it looks like all
> four of them can be loaded up to about 5A individually before the
> voltage falls out of spec (10/20 V)
>
> So I've been playing around with KICAD and come up with a design
> with three Traco TEN40WIR DC/DC converters (2x2411 + 2423) running
> off the +/- 10V rails, and I'm seriously tempted to try order a
> PCB just to try it out...
>