Need help for reparing a ISOTECH IPS-2303 PS / GW INSTEK GPS 2303

[JacquesBBB]

Dear All,

In the ISP-2303 power supply  (2 0-30V 3A channels, also known as GW INSTEK GPS 2303), there is a push button for activating the output.
If this is not activated,  all   displays are set to zero ( see picture).
When you press the toggle button, the output becomes as normal.

But in my unit, it does not work.
If I press, nothing happens.

I have started to dismount the unit (see pictures).

From my preliminary analysis, the button should toggle one of the relay trough  the MC14013B flipflop chip, but as I do not have the schematics,
my progress are slows.

If anybody has the schematics, this would be great.
Otherwise, if some one has some experience in this PSU, any help would be welcome.

[JacquesBBB]

Really, nobody knows anything about this power supply ?

[2N3055]

Well,
on photo output switch looks bent.. If that is not just a distortion on photo I would start from there...
Measure on a switch if there are voltages on it and if there are changes when you activate it..

How did it happen? Did you buy it broken? Did it work before? Was there something that happened after which it stopped working?
There are several fuses inside..
These are analog PSU with digital voltmeters/ampermeters. They can be traced component by component.
I don't think schematic is publicly available...

[simba15]

So I have made a few repairs to one of these supplies.

But my issue has been with the display module,  the fuses blow and need replacement ( so I made external holders).

I would check all fuses and start looking for voltages measurement points.

[JacquesBBB]

@2N3055

I got the unit in this state. I suppose it worked before otherwise it would have been  returned .

I have the shematic for the GPD units, but this is not of great use as  GPD are controlled by a PIC MCU.
I have a tuning manual for the GPS,  but it does not contain schematics.

The output switch is functioning well. The problem does not come from the switch itself.

This switch (push button) connects the pin 4  (R) of the  4013 flipflop  to GND ( VCC of the 4013) . VSS of the 4013  is -15 V.

C and D of 4013 are to VSS
S is  to VCC (GND)

 
@Simba15

The fuses look OK . I will nevertheless test them next week end ( I have no access during the week).

[2N3055]

@2N3055

I got the unit in this state. I suppose it worked before otherwise it would have been  returned .

I have the shematic for the GPD units, but this is not of great use as  GPD are controlled by a PIC MCU.
I have a tuning manual for the GPS,  but it does not contain schematics.

The output switch is functioning well. The problem does not come from the switch itself.

This switch (push button) connects the pin 4  (R) of the  4013 flipflop  to GND ( VCC of the 4013) . VSS of the 4013  is -15 V.

C and D of 4013 are to VSS
S is  to VCC (GND)

 
@Simba15

The fuse look OK . I will nevertheless test them next week end ( I have no access during the week).

Now trace from Q1/_Q1 (PIn 1 and 2) to something that drives output relay. Do FF outputs change when activating switch?

If there is no output relay, then it will go somewhere to disable output

[JacquesBBB]

Now trace from Q1/_Q1 (PIn 1 and 2) to something that drives output relay. Do FF outputs change when activating switch?

If there is no output relay, then it will go somewhere to disable output

Yes, this is what I started to do. I cannot verify, as I am  out of my workshop place during the week, but it seems to me that there was no changes when I
press the button. I  thus thought that the 4013 chip was bad and I changed it ( I put a socket for the future).
Unfortunately, nothing changed. I left the device as is, but will resume the analysis next week-end and will provide  more quantitative information.

What I thought is that  there may be a short circuit after the 4013 that prevent the  Q or Q_ pins to change state. But I did not have time to verify this hypothesis.

[ingalopez]

Besides the output relay (have you located it?), is there voltage on the power supplies you can regulate with the knobs? (prior to the relay). If it is, then check the relay and its driver. As you  replaced the 4013, there should be a bad transistor (or ULN 200x section) that drives the relay, provided the power for it does exist (same as the steps relays?)

[JacquesBBB]

Hello to All,

I still do not have the schematics, but try to progress on the repair of this unit. It is slow because I am not retired and do that only part time. I have several others
power supplies and try to fix this one just for the fun of it.

I have made some progress.

- As I have another unit, I could switch the boards and definitely  rule out any problem on the power board.
- Moreover, I know  definitively that the problem comes from the MC14013B, or more specifically from its surroundings.

I have isolated the problem. The push button puts R2(4) in contact with S2(6) which is normally at VCC.

At present, it does not do anything  because R2 is already almost at VCC. As soon as the power supply is barely hot, the resistance between 4 and 6 is around 600 Ohms. But if I redo the measurement after power down and waiting a bit, I find rather 25 k.

I've already looked around a bit, but haven't found yet. I know that everything works otherwise, because if I put pins 2 and 3 in contact, I trigger the outputs and everything is OK.

By chance (I had forgotten to put the 4013 back on its socket), I also saw that the power supply works very well without the 4013. In this case, you cannot switch the output, which therefore always remains active. I admit that it's not really a problem, and I'm almost tempted to reassemble everything as it is, but since I'm not particularly in a hurry, I leave the beast disassembled for the moment, while waiting to find the culprit.

If anyone has a good idea on what likes to go from 25k to 500 ohms between cold and barely hot, I'm interested. I suspect a transistor but with an intermittent failure of this kind, tracking is not easy and can only be done under voltage.

I already removed capa C505, but it's not her. To make matters worse, the components are 603s.