| Electronics > Repair |
| Korad KA3005P power supply faulty/repair |
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| pomonabill221:
--- Quote from: AllanMN on January 28, 2014, 05:00:47 pm ---Ah. Found it. The fan wire wasn't routed through the slot in the fan housing and was then crushed when assembled, shorting to case/ground. What I saw on the scope was the PWM of the fan return, pulled low by U12, an On Semiconductor ULN2003A High Voltage, High Current Darlington Transistor Array. Splice or replace to repair. A comment I saw on the video EEVblog #315 - Korad KA3005P Review/FAIL : " The biggest problem with these 1HL brands is the counterfeit pass transistors. They can barely supply 1/3 their rated current due to a severely reduced SOA. I routinely buy them - they're a steal - and replace the pass transistors with the genuine parts. I never, EVER have problems again. I am very hard on power supplies and do everything I can to blow them up. " Any thoughts if this mod is warranted? And details? If say, you are inclined to charge SLA batteries at 5 amps for a few hours which I would not be? Cavlovic killed his doing this I believe. Did you ever figure out how, or get a repair/replacement? I wonder how hot the sink gets at a full dissipation. I don't have a thermocouple to check but will in a few weeks. The overshoot isn't such a concern to me if it only happens at 3-5A load ranges as in Dave's video. Do you see that too, Bill? All my voltage outputs are very accurate. I guess I like this PS for the money. Even if I have to fix it! Allan --- End quote --- Did you look at my PDF of the schematic? They are using three drivers for the fan, then two more for each relay, and one is spare. |
| AllanMN:
--- Quote from: pomonabill221 on January 28, 2014, 09:11:16 pm ---Yes, the overshoot does change depending on the load. I do see overshoot at even low loads (although I don't remember what the loads were and what the overshoot was.. will have to try it again). --- End quote --- Ah. Well, that is a FAIL, and would be a thing to fix if it's very significant. Or at least know about. I haven't checked into that yet. --- Quote from: pomonabill221 on January 28, 2014, 09:11:16 pm ---I was charging a 24V battery once, and drawing max current from the supply, and it did shut down due to over temp on the heatsink (or thermostat in the xfrmr... really don't know which tripped), but after a while of cool down (about 10 minutes), it powered back up ok. It was running pretty hot and the thermal overtemp seemed to do it's job. The heatsink is a little small if you are going to push it, and I may mod it with a larger heatsink (maybe even a larger fan), but for now it is working great for a cheapie! I know alot of people whine about how cheap it is, and all it's problems, but like I have said, it ain't an HP/Agilent/Lambda/Fluke/etc., and I know that. One thing on my supply... the FWB was NOT bolted to the heatsink and they relied on the stiff leads of the bridge! It was NOT laying flat on the heatsink (the lead side was not touching the aluminum), so I desoldered the leads, bolted the bridge on the sink, and resoldered. How cheap was that! I would suggest that you check the mounting of the bridge to make sure that at least it is making good mechanical contact to the heatsink, and maybe even bolt it down... it probably runs pretty hot when under high load and will not last too long. Here are some pics of the bridge (notice the slight space on the lead side), the xsistors and bridge (notice how the goop doesn't look like it was making contact on the bridge), and the contact area on the heatsink (only partial contact on the bridge). --- End quote --- Good to know. Yes, the sink is small, and maybe simple to improve. I might have some 1/8" Al sheet around to cut and bend up. I'll definitely check the bridge when I replace the fan. Doug is sending me another to avoid splicing leads. Seems colvinic (?) toasted his charging batteries and we haven't heard any more. --- Quote from: pomonabill221 ---Did you look at my PDF of the schematic? They are using three drivers for the fan, then two more for each relay, and one is spare. --- End quote --- Most definitely! That is a great contribution and I thank you for it! |
| pomonabill221:
Did you think I had to splice the leads on the bridge? I'm sorry I wasn't clear about that... there was enough lead length on the bridge (at least on mine), that I didn't have to extend or splice onto the leads.... Yes, the overshoot is surely something that I intend on looking into when I have a little more time. Trying to rely on remembering to disconnect the output when switching on, or having to add a relay to the output (which I still may do for several reasons), doesn't fix the problem and I would like to fix the problem... just a personal "goal" or triumph! hehe I am glad that those of you that have downloaded my crude hand drawn schematics have found them useful. I really tried to be accurate, but if you find something that isn't correct PLEASE let us all know! OR if you have a question about my drawings, don't hesitate to ask! (sometimes I have to ask MYSELF "what the heck did you mean by that??") As crude as the software is, I still can't get it to work on my win7 64 box! It keeps asking for matlab, and I don't have that! And WHY would it need it anyway? Just chalk it up to "crappy software"! It would be nice though. |
| commongrounder:
@pomonabill221: That's interesting about the software needing Matlab. I'm wondering if the there is a runtime Matlab application embedded in the Korad software that isn't 64bit compatible. If that were happening, when the program attempted to start it would not find the runtime app functioning and issue an error message. Korad programmers may have used a Matlab core to build the graphing and analysis (as much as there is of it) portion of the program. I spoke with my son, who is a programmer and has used Matlab. He thinks you could look in the folder that contains the program files for the Korad software, and see if there are any files that are Matlab related. There might be a 64 bit version available that could be put in place to fix the problem. |
| pomonabill221:
HHmmm.. that could be what is going on! I will take a look and see. thank You. |
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