[time-nuts] HP5370 power supply measurements
Rami Vainio
rami.vainio at gmail.com
Wed Jul 13 11:19:17 EDT 2016
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...
>
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