Pretty stupid to expect a decent answer without telling what model it is.
A service manual of the supply should help. From the looks of the schematic of the power supply/transformer area, there are at least 7 fuses that you could check as well as a number of voltages and filter caps. Because there appear to be multiple symptoms this is where I'd start looking.
https://elektrotanya.com/gw_instek_gpd-2303s_3303s_4303s_sm.pdf/download.html
I'd use a DMM with a continuity function to trace from one prong on the power plug through the primary circuit to the other prong. Since the unit isn't plugged in to mains while you're doing this, you can poke, pry, and shake things as necessary to find the bad connection without worrying about sparks and smoke.
Ed
I'd use a DMM with a continuity function to trace from one prong on the power plug through the primary circuit to the other prong. Since the unit isn't plugged in to mains while you're doing this, you can poke, pry, and shake things as necessary to find the bad connection without worrying about sparks and smoke.
EdThanks for the suggestion. I actually already tried this and as I mentioned in one of my earlier posts I measured a constant 640 kohms from one prong to the other when the main power switch was closed, for all of the different AC voltage settings. This resistance seemed a bit high for the primary of such a large transformer, so I would guess it might be the AC selector switches (seems unlikely) or the neutral line is flaky (on the selector board or, Heaven forbid, within the transformer itself).
I'll be looking more into this after work tomorrow.
Cheers,
Matt
No, you measured resistance. I'm talking about continuity. You know - the little beeping thing. You could use resistance, but this is what the continuity function is for.
Go step by step from one prong around to the other and find where the beeping stops. The list will be something like power cord, power switch, fuse, voltage selector, transformer, maybe the power switch again, and finally power cord again. If there isn't an exposed spot to probe, use a tiny pin to puncture the wire insulation. Your path will test each item one after another. If you don't get a beep, the previous item is the defective one.
EdI am familiar with continuity testers. The problem is that, unfortunately, the continuity test function on my multimeter is based on resistance. Some meters may supply a higher voltage in continuity mode but if I remember correctly mine does not - it is very cheap. With my meter I get more information by measuring resistance than I do from the continuity test. I could probably hook up a 9-12V battery and a meter or something and test continuity that way.Posting clear, in focus, high resolution pictures will help if we can't find a service manual.
I will see what I can do when I get home from work
No, you measured resistance. I'm talking about continuity. You know - the little beeping thing. You could use resistance, but this is what the continuity function is for.
Go step by step from one prong around to the other and find where the beeping stops. The list will be something like power cord, power switch, fuse, voltage selector, transformer, maybe the power switch again, and finally power cord again. If there isn't an exposed spot to probe, use a tiny pin to puncture the wire insulation. Your path will test each item one after another. If you don't get a beep, the previous item is the defective one.
EdI am familiar with continuity testers. The problem is that, unfortunately, the continuity test function on my multimeter is based on resistance. Some meters may supply a higher voltage in continuity mode but if I remember correctly mine does not - it is very cheap. With my meter I get more information by measuring resistance than I do from the continuity test. I could probably hook up a 9-12V battery and a meter or something and test continuity that way.
More info isn't necessarily good info. Everything on the primary side of a linear power supply is very low resistance. I just measured the resistance between the prongs of a 50V, 5A linear variable lab supply. I measured about 3 ohms - including the lead resistance. Trying to measure resistance in that situation is a waste of time. You've got a bad connection somewhere. The continuity test is the first test to try in a situation like this. You don't need a higher voltage.
Ed
It occurred to me that I was measuring the resistance of the primary side of a step-down transformer, so the resistance will be rather high.
Ed, I'm not sure how you measured only 3 ohms on the primary. That seems absurdly low...?
That being said, there is continuity between all of the primary taps, there just seems to be a high resistance (higher than expected - ranging between 600K and 1M) between the hot "leg" of the transformer and the taps. Perhaps this is normal but it still strikes me as a little high. I'm a bit concerned that it may point to a damaged primary winding which I assume would be BER.
Also, for the record, some of you seem to be talking down to me like I'm a complete newbie. I wanted to make it clear that I am an Electrical Engineer by profession and understand the basic concepts behind the design of power supplies. You can speak in technical terms and I will understand, you don't have to dumb it down for my sake. This is just the first power supply I have ever tried repairing, so it's a learning experience for me.
You're making DC measurements on the primary of a transformer. It doesn't matter what the secondary is.
No, it isn't. I wandered around and made some measurements of the primary circuits of a few devices as follows:
HP 6622A Linear Power Supply (160W output) - 0R9
HP 6002A Linear Power Supply (200W output) - 0R8
Goldstar GP-505 Linear Power Supply (250W output) - 1R0 -- This is the unit I originally measured. Looks like the switch was a bit dirty when I made my initial measurements.
Then I measured a mil spec. hermetically sealed 360W isolation transformer. 110V in, 110V out. Nothing else. It measured 1R6. Note that unlike my initial measurement, these measurements do NOT include lead resistance.
Are you beginning to see the pattern, Matt? Your power supply has a total output of 195 watts so you should be seeing similar numbers.
These devices that have 110/220 switches typically have two primary windings. They run in series for 220V or in parallel for 110V. Since the 3303 has 100/120/220/230 volt settings, you should have a total of 6 wires coming from the transformer to the voltage selector. That's consistent with your drawing showing J102 and J103. But the gray wire doesn't seem right. Can you recheck that? With J102 and J103 unplugged, is there continuity on the transformer side of J102 and J103 between them or is the continuity only within each connector?
Don't forget that you've never seen this thing working. Maybe someone else got to it before you and messed up the wiring.
Seriously, on a forum like this, there's no way to tell if you're talking to a kid in high school or a grey beard who's forgotten more than most of us will ever know. I really do have a grey beard, but I haven't forgotten everything ...... yet ..... I don't think.
Curiouser and curiouser.....
If there's continuity between J102 and J103, your AC selector drawing is wrong because it shows multiple taps being shorted out. There will be smoke! However, if J102 and J103 are two separate, identical coils, then your drawing works as described below.
BLU and RED = 115V
YEL and BRN = 105V
ORG and BLK = 0V
S102/S103 Switch Positions (Left or Right)
LL = BLU/ORG in series with RED/BLK = 230V input
LR = BLU/ORG in parallel with RED/BLK = 115V input
RL = YEL/ORG in series with RED/BLK = 220V input
RR = YEL/ORG in parallel with BRN/BLK = 105V input
Please check your drawing and my tracing to make sure they're correct. While you're at it, is there an unused solder hole on the AC selector board that would connect to the black wire? I have a theory....
Ed
If you get no continuity from the primary-common to the taps, then the primary common is open. You should get continuity between taps, and high Z to the secondary.
The panel meters lit up intermittently, so you should be able to poke and prod to find the location of the break.
If you are sure it's the transformer, take it out and try surgery- unwind the tape and get to the primary-common winding/wire connection. Unless you can find a "dent" in the winding, if the transformer got banged during assembly.
Ask GW Instek for cost on a replacement xfmer.
The problem with repairing the transformer is that typically, the low voltage secondary windings are on the top and the primary is buried underneath. So you'd have to unwind everything to get to the bad connection on the primary. But you might not have to do that ......
Keep the following things in mind:
- notice the goofy solder connection for the grey wire. It's soldered to a brown wire stub that goes to the power switch board. Looks to me like a last minute design change.
- notice the two blue wires and the other brown wire that are in the same connector as the brown stub.
- the voltage selector wiring is totally ordinary except there's no connection between the black wire and the hot side of the line.
Here's my theory. I think that the brown stub originally went to the voltage selector board and connected to the black wire. The grey wire wasn't used at all. But then they realized that they should have used the grey wire so they made the design change. Why? Maybe the grey wire has a thermal fuse and the black one doesn't but otherwise, grey and black are the same. I realize that right now, there's no place on the voltage selector board to connect the brown wire and I'm really annoyed at that!
So what am I proposing? Matt, are you up for some more testing? Do you have access to a variac? I'd like you to connect the variac between the black or orange wires and the blue or red wires. With the voltage selectors set to 115V that should put the variac output across the two windings in parallel just like they should be. Disconnect the transformer secondaries from the circuit. Monitor the current out of the variac and the voltage across one of the secondaries. Start the variac at 0V and slowly raise it while watching the current. If everything is correct, I would expect to see a current of less than 200 ma. with full line voltage across the coils. The voltage on the secondary can be compared to the capacitor voltage that it connects to.
If this test works, you can just abandon the grey wire and jumper the brown stub over to the black wire on the voltage selector board.
Ed