Electronics > Repair
Keithley 2602 repair need help!
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smaultre:
Hello i have two channel sourcemeter 2602 with one bad channel.
Bad channel get full amplitude on output. That's cause one channel power supply to overload.
On the bad channel:
One of LM337 near the capacitors gets hot, and one LM317 have the room temperature, on working channel they both gets quite hot
I thinks, that it's because one part of pre-amp eat more current.
I try to trace and found one bad smd transistor Q32, marked as 2.(dot)A LLI      2.A LLI
Looks like 2n3906 or maybe some different type?
It's connected with diode(zenner?) VR7

When i de-solder bad transistor and check it with transistor tester. That shows that its BJT-PNP with hFe=0 Ic=0 Ube=0 (BAD).
Then i check resistance to GND from solder pads on PCB and it's shows near the working-one channel resistivity.
I try to put these transistor from a good channel and powering up my 2602 with one connected channel.
Oscillations stops power supply doesn't goes to protect mode, but i have +2.48V on output.
Ok, then i  trying to put back Q32 to working channel, transistor tester shows that it's BJT-PNP with hFe=176 Ic=1,6mA  Ube=658mV (Good ?)
When i put it back on previously working channel it shows on  output  -2,68V

Now two channels are bad. |O

UPD, extracting another one same as 2.A LLI from non working channel, i'll bring previously working channel back..
Zucca:
I am sure you already looked here:
https://xdevs.com/fix/kei2425/

It is a K2425, but it could be a good source to narrow down your problem.
smaultre:
The product lines 24xx & 26xx have different schematics..
smaultre:
What is the part type?  2n3906 ??
smaultre:
https://www.eevblog.com/forum/repair/keithley-2602-dual-smu-repair/


DONE!
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