Hello fellas,
indeed this is a tricky one for a noob like me. Lots of scrubbed off components and also I'm slightly unaware of how signals should look like exactly at each point.
Only ever used siggens that were working, first time poking into one
However! I am measuring 5 V and 0 V at what I believe should be an output of + / - 12 V at the places where Mechatrommer indicated in his pics of the PCB.
I am probing ground at the wire that's floating between jumpers above and through the FPGA heat sink. I.e. the ground from the 5V/2A power supply.
I imagine that the +/- 12V are with respect to that ground, please correct if wrong?
Pic attached: note there is 0.5V DC offset and Vpp is very weak (frequency is correct but Vpp should be 4V).
This is reading either channel of the siggen on CH1 of the scope
CH2 of the scope showing 5V at +13 V probe point on the PCB.
Further probing reveals:
5V where it says +13V
0.75V where it says -13V5V further back where it says 5V
0.75V further back where it says -5V. 1.2V and 3.3V probe points are OK.
Looks to me like those negative power rails are the issue, since having a DC offset and too low Vpp happens identically on both channels. Am I on the right track?
Some solder joints look like they can use a reflow but continuity is still fine wherever I found this.
Turned power off. Forward-bias probing the diodes with the 121GW gives me 0.18 V on both, reverse-bias probing them gives 1.5V / 2.1 V.
In resistance mode, forward-bias on both diodes is giving me 2 kOhm. Reverse-bias is 100-250 kOhm on the "upper" diode (Mechatromm's pic frame of reference).
The "lower" diode is showing 2M-ohm reverse-bias resistance.
Not sure if those values on the diodes are as bad as it looks to me, or if it's normal because of the particular +/- power rail circuit configuration.
I did try to uncharge all caps before probing the diodes (power off ofc).
The last thing I tried was checking that XL6008. It's supposed to be the voltage regulator right?
Enable is high (5V), feedback pin 0.5-0.75V, both Vin and Switch out are a constant 5V. It looks to me like switch out should definitely not be a constant 5V?
I changed the Vpp to 10V on the siggen, but after hearing relays click I'm reading the exact same thing out of the voltage reg.
Could this be the culprit or at least clearly one of them?Any further tips on how to find out exactly which component is failing how?
Also from my fellow Swiss resident, I am having trouble finding shops that easily deliver electronics components to private customers.
Stuck with Conrad at the moment using work e-mail. Any other tips? Is there a cool secret Swiss radio shack I don't know about?
I feel close to a solution here. Or is it more like
?
Either way sorry for the delay, life gets in the way sometimes. Thanks a lot for the help. And a great 2021!