Rhino PST-2500M review. This thing was powering a US$7,000 equipment! - Page 1
Forum section: electronics / general

author: rsjsouza
author_rank: Super Contributor
timestamp: December 18, 2012, 05:47:58 am
content: SPOILER ALERT: no equipment was hurt in the making of this thread.A few days ago I was lucky enough to receive a JTAG in-circuit debugger pod from a colleague and I put it for a spin - averyexpensive one. While setting up the whole thing I noticed the wall adapter was a generic switching power supply with a rotary switch for the output voltages - obviously not the original one but it was somehwat beefy at a promised 2,5A. Alarmed by this (my history of blown up equipment with wrong voltages is quite large) I double checked the output voltage setting (8,4V?!?) and the input voltage of the JTAG pod (7-9V). Although the pod disconnected itself from the target board after several minutes, everything worked fine.Today I took a second look at the wall adapter and, still suspicious of its quality, I searched around on the internet about a teardown and a technical review. None was available, thus I brought it home and decided to take a closer look.Before opening it (as its housing is glued), I decided to evaluate the output voltage and current. Set the unit to its setting of 8,4V and measured 8,2V with no load... Started somewhat bad, but oh well. Then I connected my usual load (10 ohms / 25W) that would give roughly 800mA of output - nothing serious for a 2,5A.The images speak for themselves...The testing rig with the load... 7,67V out and the Rigol says 1,V Vpp (which may be also a quantization error... not sure).The Rigol screen on DC coupling...The Rigol screen on AC coupling...The testing rig again, this time with the DMM measuring current... Roughly a third of the maximum claimed capacity!And then the teardown...Opening the box. Lightly Glued on the sides, it was not hard to open it.The voltage selection switch. Pretty cheap and severely flaky - hey, the user's manual says you can't switch voltages when powered on. Now I know the reason!Samson 105C capacitors, average quality of the transformer, good strain relief on the wire. I would say it does not look too bad.High voltage caps. Still Samson 105C. Not too much area on the MOSFET heatsink. The slanted board is where the wall pins are connected.The wall input board is very empty. There is a miniature fuse on one of the inputs. The creepages do not protect anything as the tracks are fully unconnected. D3 is the only SMD diode of a full bridge of 1N4007s - the other three are through hole and are on the other side of the board. The outlet input at the bottom is too close to the positive output of the rectifier. No suppressing circuit of any kind. This is the lowlight of this power supply.A side view of the wall input board. Nothing much interesting here, just three 1N4007 diodes and a fuse in the middle.The main board top view. The heatsink on the left is the double schottky diode (MBR101000) and the one on the right is the MOSFET switcher (SVD4N65). There is a blue Y cap in the middle and an opto-isolator at the top. IC2 (top left) is a TL431 reference.The main board bottom view. Soldering work is ok, and D5 is an eyesore. Some nice solder in high current tracks and a very wide separation between the high and low-voltages.The two high power devices in their heatsinks (the schottky is the one with white thermal paste on it). IC2 in the front, IC1 in the middle (the opto-isolator) and a PNP transistor (M28S) lying flat face on the left.Main board outside of the housing. The output wires could use some glue (although the strain relief is really good) and I really don't think this is a RoHS product.I think the overall build is somewhat above average, but the input board is absolutely hideous. If the performance was ok I would be satisfied with the product, but I don't think anything justifies an 8% drop on a 30% load.Rhino PST-2500M manualMOSFET SilanSVD4N65 specsheetand an interesting presentationhereSchottky rectifier LunsureMBR10100

author: amyk
author_rank: Super Contributor
timestamp: December 18, 2012, 12:21:05 pm
content: Is that voltage selection "switch" really just a pot since it only has 2 wires?The ESR on the output caps might be too high, or they've dried up and their capacity too low, to cause that ripple.

author: AndyC_772
author_rank: Super Contributor
timestamp: December 18, 2012, 12:44:37 pm
content: The noise on the scope is unrepresentative, and is entirely down to poor measurement technique. To get a representative measurement of how much noise would actually be seen by a load, you need to measure directly across a good quality ceramic capacitor using a probe with a very short ground lead.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 18, 2012, 01:14:38 pm
content: Quote from: amyk on December 18, 2012, 12:21:05 pmI haven't thought of that. It may be that or a series of resistors soldered to the small PCB (you can see some traces through the board)Quote from: amyk on December 18, 2012, 12:21:05 pmThanks for the tip; I will replace with some spares here and see what I get. But I don't think I will put that into the emulator pod again...Quote from: AndyC_772 on December 18, 2012, 12:44:37 pmThanks for confirming my suspicions. I didn't trust that number either.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 19, 2012, 01:09:39 pm
content: So, I replaced the caps and amyk was right on the money: it affected the output voltage: at no load it went up to 8,42V, and at the 10 ohm load it went down to 8,15V.The ripple measurement using the ceramic cap was also reduced (before replacing the caps I measured around 250mv and it went down to 150mv).However, yesterday I also found another wall adapter from LZR electronics (LZUSD02002A0200 - 9V @ 1,9A) that proved to be a very nice replacement: 8,99V at no load, 8,78V at 1,6A load, 100mV ripple under load. Yep, I think I will stick with that one for this JTAG pod and use the other one for less critical tasks...Thanks again for the suggestions and comments!

author: SeanB
author_rank: Super Contributor
timestamp: December 19, 2012, 03:30:01 pm
content: That is why i love using the good old fashioned magnetic transformer. Much lower noise.