305D power supply not working and missing parts? - Page 1
Forum section: electronics / repair

author: DixonSteel
author_rank: Newbie
timestamp: July 28, 2016, 01:29:46 pm
content: Hi everyone,I am new here but I found this site and some schematics for this supply here, so I wanted to try posting here. I bought a PS-305D supply and unfortunately can't return it since I never thought of testing it until I needed it.The problem right out of the box is, the current meter side has a reading and seems to adjust, with no load on the supply. The voltage meter side reads all zeros. Putting an external meter on the supply, I read nothing as far as voltage goes.I found what I think are accurate schematics here:https://www.eevblog.com/forum/repair/new-power-supply-ps305d-not-regulating-and-running-over-voltage-and-current/Doing some investigating, it looks like I am missing parts and connections for the meter section along with the no voltage problem.Can anyone tell me if R212 should be present and what its value is? Also can anyone tell me if CN302 connections are really used since I am missing R212 and CN302 is not connected. Any suggestions for the voltage not working would be great if anyone has had similar problems with this supply.I have attached a couple of pics on what I am seeing.Thanks for any help.Me

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 28, 2016, 02:28:01 pm
content: If you can adjust the current but not the voltage it sounds like your output is shorted.Can you measure the resistance on the output while the supply is off?

author: DixonSteel
author_rank: Newbie
timestamp: July 28, 2016, 02:31:05 pm
content: Yes, I can and will do that when I get back to my lab later tonight and will post the results. Thanks.

author: DixonSteel
author_rank: Newbie
timestamp: July 29, 2016, 12:48:04 am
content: PAOPBZ I measured the resistance on the output while the supply was off and it measures open or infinity. The only weird thing was the meter beeped like it was a short when I first hit the probes on it but then measures as an open. I was thinking of maybe trying to isolate the sections and see whats coming off the main board?

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 29, 2016, 10:07:49 am
content: Your measurement is normal, what you see is the output capacitor getting charged so at first it looks like a short. The next thing to do is check the + and - 15V and the output of the main bridge rectifier (across C101). Can you describe what you see (and hear) when you turn the voltage and current controls? Are K101 and K102 doing anything?I don't think you are missing parts and/or connections, it is common practice to use the pcb's for different models.

author: DixonSteel
author_rank: Newbie
timestamp: July 29, 2016, 11:49:54 am
content: Thanks, I will measure this, but may not get back until tomorrow I am on the road today for a while. When I turn it on I hear nothing, I don't even hear the relays switching. I noticed a lot of the solder work is sloppy.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 29, 2016, 03:50:11 pm
content: The missing R212 is somehow connected to the display driving. So it would have an influence on which digit is lit. IT might be an option for different versions. As there seems to be a valid number on the display (even if just 000) this should not be a problem. Still strange to see R212 unpopulated and not R213 together with CN302. CN302 might be for an other version too.I don't think the schematics from the other thread is fully accurate (I would not expect is to work this way, at least one more resistor or diode replaces be a resistor). So maybe R212 and R213 have changed too.There is no absolute need for the relays to switch on turn on. It's well possible the first one only turns on if the real output voltage goes higher than about 6 V. With no output, it can be Ok to have the relays off. Even with the relays not switched the regulator should at least work for low voltages like 0-8 V.As R212 / CN302 are for display only, they should no be the reason for no output.

author: DixonSteel
author_rank: Newbie
timestamp: August 01, 2016, 11:32:25 am
content: I looked over the main board over the weekend and what I found was there are these variable resistors that needed to be adjusted to get the 30 volts output. So, I now have 30 volts output verified with an external meter. The problem still is I am getting 5amps out no matter what. This part I can not figure out. I can vary the current a little bit, but for the most part its pegged at 5 amps. The main board is weird, there are caps where there should be resistors, again I don't know this is just model differences?Anyone have any idea why I am getting max current no matter what? I don't see any obvious shorts so far.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 01, 2016, 08:22:57 pm
content: The question is: is it thinking that you have a 5A current running or is it just the setpoint for the maximum current? If you have a wattmeter can you see how much power the PSU is drawing from the mains? Is anything getting warm? Can you adjust the voltage from 0 to 30V? What is the range you can dial on the A meter?Can you set it to 12V and then connect a car headlight to the output? What are both meters showing before and after you connect the lightbulb?This might be of interest too:https://www.eevblog.com/forum/repair/wepyihua-ps-305d-power-supply-current-sense-circuit/

author: DixonSteel
author_rank: Newbie
timestamp: August 02, 2016, 11:43:23 am
content: I put some resistors across it and it seems to be putting out the 5amps. I can't seem to adjust it much lower and the over current light is on. I don't have a watt meter, I could break the line and measure the current. Nothing is getting warm, I thought if I left it on something would, but nothing does. Yes, the voltage will adjust.I will try a light bulb, I didn't trust it to try and power anything else.

author: DixonSteel
author_rank: Newbie
timestamp: August 04, 2016, 01:02:22 am
content: Well, I went back to look at the supply more and it seems the resistor adjustment didn't last or maybe just stopped working when I put it back together. At this point I'm beginning to think its junk unless I can find an accurate schematic.

author: aa0cn
author_rank: Newbie
timestamp: June 22, 2021, 07:17:55 pm
content: @DixonSteel if you still have that old PS-305D around, here are some schematics for it...I did a finals repair on my PS-305D, you can find schematics for this unit here:https://aa0cn.neocities.org/ps-305dm.htmlOr from PierAsia on his site here:https://www.pieraisa.it/php/myHwProjects.htmlLooks like pretty much all the parts are available on AliExpress, and I fumbled around with the realignment (but would appreciate if anyone knows the "right" way to do it!)

author: DixonSteel
author_rank: Newbie
timestamp: June 22, 2021, 08:17:39 pm
content: Actually its still here, I was going to pillage it for parts but now maybe I'll fix it. Thanks for the data.