Problem with my anushri synth

Hi,

The resistance between the -5V circuit and the GND is average 0.2 ohm
I think is a short circuit

I removed all chipsets, capacities in the -5V circuit. It remains only IC sockets and the resistance is still average 0.2 ohm.

Can someone help me?

I would like to remove sockets but i’m afraid to damage the main board

What would you expect to find beneath the sockets… for 0.2R you should check for simple shorts on adjancent Pads. Post HighRes Pics of your Boards here, we can help you spot the problem.

Thanks, i’ll do

Hi,

Here are pics of the main board. I hope you can help me.

C44 looks slightly weird.

C22, C24 missing, IC3 partly unsoldered, IC4 looking really bad, C14, C19 missing, R25 Missing (THATS FUCKING PART OF THE FEEDBACK LOOP OF THE SAW CORE!), C31 Missing, C22 Missing, C33 Missing, C44 looking destroyed, C48 Missing, C49 Misssing…

And some of the Pads around the 7905 might have burnt the Soldermask thus shorting to GND.

To me it looks like some early attempt I did with lead-free solder.

Thanks for your answer.

At first when i finished to mount my synth and switched on, nothing happened. I quickly saw i mounted
7905 and 7805 on correct location (I didn’t invert) but upside down. The tension at point 2 (LT1054) was 8.5V (I used a 9V DC 500mA supply) and was -3.2V at point 3. + was OK ( so C44 are OK) but -5V not.

I removed LT7905 and LT7805 because they were upside down, I obtained -8.5V at point 3 (LT1054).
I looked the schematic and I visualized all components on -5V circuit.

Thereby, I removed one by one components spotted on the schematic of the main board. That explains why C26, C27, C15(not C14), C18 (I had to remove R25 to C18, it’s not C19), C31, C33, C24, C40 and C44 missing.

IC3 partly unsoldered because I started to unsolder because I thought the issue could come sockets. If you look on the main board GND is right next to -5V in sockets IC3 (That explains the pics and my message of june 6), IC5, IC7, IC9 and IC10.

Today, i removed C44, I tested it and it is OK and there are no problem on +5V (C44 is on this circuit). I still have my problem.

Concerning the pods around the 7905, they burnt when i removed the 7905 upside down (altouhg i took a lot of time to remove it : i warmed very slowly) but I already had a short before disassembly.

@tb323, i used a solder with lead…i’m so bad :(. I have already mounted some simple kits with less caution and i haven’t had any problems. How did you solve the problem of solder?

Do you think there are other components that could be causing the problem?
How can I be sure I burn the soldermask at the 7905?
Do you think the problem started since i mounted the 7905 upside down?
What procedure do you recommend me from now?

Most of the 100nf capacitors are not needed. I would look at the solder connections on the sockets, some of the pins need re-soldering, here is an example.

I have just re-read your message, is this unsoldered because you want to replace it? If so then keep going and replace it. You can buy “Solder braid” or a “solder sucker” to remove the solder.

The PCB looks un-damaged so if you go slowly and replace the parts one at a time you will fix it.

Also, I would not worry about removing capacitors to test them, the small capacitors can have negative voltage on them and survive, they are “unpolarised” so they don’t mind having + or - voltage on them. When components like capacitors and resistors fail they usually go black or burn so you would know about it. Chips however can fail very easily and it is hard to know.

maybe also take the 1054 out and check if the short is still there with no ICs at all.
i couldn’t spot any obvious bridges from the pics.
what fcd72 mentioned (damaged pad shorting to ground) could be possible too but from my own experience they rather lift off instead (don’t ask)

tantalum caps usually produce a short when they die.

@Brun_De_Nurb: I switched to leaded solder and bought a lot better soldering station. The one I had before was really bad and couldn’t keep the heat. :slight_smile:

Hi,

I’ve started to disassemble sockets, it’svery long and i still have a short. I really hope to succeed.

As stated before - what do you expect to find under the socket?

You will most likely do more damage then this helps.

in this case i would start with removing parts that are known to be capable of shorting when dead, just 1 or 2 iirc

@fcd72

I hope to solve my problem of short circuit on the PCB.

Hav you corrected the failure mentioned above? Without proper Equipment you will 100% wreck your Board…

@rosch

That’s what I try to do. In my second message of june 9, I think I did a quick summary of the first things I started to do.

But thank you to both. I feel less alone with my problem