(Need help) repairing a faulty Velleman PS3005D (Korad KA3005P) power supply

[Kevin.D]

Isn't there a chicken and egg problem when it comes to using Vout for setting the relays? The relays are needed to get the higher voltages at the output, so how can you use it to set the relays in the first place?

Edit:

The Vset actually does change when the output is limited in CC operation, so I think it is a candidate for driving the relays in the same way they were originally. I'm not saying it's a better way than what you proposed, I just still have the question posed above when it comes to using the Vout measurement for driving the relays.

You go  upto the next range a few Volts before you reach a ranges max Vout .

Bed time for me .  good luck

ps :- I dont think your actually measuring TP1 there (the gnd of tp1 is +Vout) .Do you have your probes on TP1 and -Vout ? in which case your actually measuring Vout+TP1.
I'd be suprised if Vset (tp1 to gnd) reflects Vout in CC mode.

[henken]

Isn't there a chicken and egg problem when it comes to using Vout for setting the relays? The relays are needed to get the higher voltages at the output, so how can you use it to set the relays in the first place?

Edit:

The Vset actually does change when the output is limited in CC operation, so I think it is a candidate for driving the relays in the same way they were originally. I'm not saying it's a better way than what you proposed, I just still have the question posed above when it comes to using the Vout measurement for driving the relays.

You go  upto the next range a few Volts before you reach a ranges max Vout .

Bed time for me .  good luck

It's possible to set the output voltage to 30V and push the output enable button. You'd then have to go through all relay ranges instead of going straight to the correct range.

[henken]

ps :- I dont think your actually measuring TP1 there (the gnd of tp1 is +Vout) .Do you have your probes on TP1 and -Vout ? in which case your actually measuring Vout+TP1.
I'd be suprised if Vset (tp1 to gnd) reflects Vout in CC mode.

You're right. I'm measuring it incorrectly. What is the point of this grounding scheme? Ground being +Vout?

As you wrote earlier, there is continuity between +Vout and 12V gnd.

Measuring between +Vout and TP1 gives much more sane measurements. Between 0 to 2.8V through the range, and doesn't change when CC mode kicks in, as you predicted.

I can see two different ground symbols used in the schematic, but I'm not sure when to measure using a certain gnd point.

[dyessgg]

I just started having a very similar problem with my KA3005D.  Where my problem differs is that I have nothing above about 18 VDC output under load (20.7V no lod). 

I hear definite relay clicks at 7-8V and 14-15V but nothing after that as I increase the output voltage setting.  I would expect a 3rd relay click somewhere around 20-23V.  Anyone concur/disagree?  Perhaps someone with a working unit could verify?

I measured the open circuit output of the transformer and saw 22VAC max.  From the schematics posted, I don't see anything that looks a charge pump, so could this be part of my problem?  Is this the same as what is seen by everyone else?

Any ideas/comparisons would be helpful.  I'd hate to start doing surgery only to find out I amputated the left leg when there was a splinter in the right hand.

[dyessgg]

I just started having a very similar problem with my KA3005D.  Where my problem differs is that I have nothing above about 18 VDC output under load (20.7V no lod). 

I hear definite relay clicks at 7-8V and 14-15V but nothing after that as I increase the output voltage setting.  I would expect a 3rd relay click somewhere around 20-23V.  Anyone concur/disagree?  Perhaps someone with a working unit could verify?

I measured the open circuit output of the transformer and saw 22VAC max.  From the schematics posted, I don't see anything that looks a charge pump, so could this be part of my problem?  Is this the same as what is seen by everyone else?

Any ideas/comparisons would be helpful.  I'd hate to start doing surgery only to find out I amputated the left leg when there was a splinter in the right hand.

OK, now I feel completely stupid.  I tore down my unit, measured voltages and signals everywhere and found that sure enough the transformer winding outputs were about half what they should have been....uh, half?  That sounds like too much of a coincidence so I checked.  Sure enough, the input power main selector had gotten switched to the 220V setting.  Switching it back to 110V solved all the problems...except reassembling this thing. 

I'm not sure how this switch could have been moved since it is reset and, being in the US, I have absolutely no reason to change the setting.  Anyways, problem solved and a stinging reminder to ALWAYS check the external stuff first!