Houston, Tx preamp repair

[kytul88]

Firstly, I want to say that you don't have to be in the Houston area, as it's a 500 series preamp so shipping would be easy. I'm just looking local for convenience.

So, here's the problem. I put together a Link Audio SSL 4k preamp, and when I plugged it in to test and calibrate it I didn't know my 500 extender was messed up and it fried something on the board. I have found that I have enough technical acumen to put electronics together and design simple circuits, but suck at troubleshooting. I tried doing it with the owner of Link Audio via pictures and typing out what the issues were and the steps to remedy the issue. But that fell short. I asked about sending it back to them for it, but since they're in Germany he said the shipping wouldn't be worth it and to look into finding a tech stateside. Alas, here I am. So, help me Obi-Wan Kenobi, you're my only hope.

 

[ccaudle]

a 500 series preamp...a Link Audio SSL 4k preamp

SL4K-E01 or SL4K-E49 or SL4K-G91?

my 500 extender was messed up

Can you elaborate? Do you know how specifically it was messed up? And you are absolutely sure it was a problem with the extender, and you didn't just get a component installed backwards in the preamp?

 

[kytul88]

SL4K-E01 or SL4K-E49 or SL4K-G91?



Can you elaborate? Do you know how specifically it was messed up? And you are absolutely sure it was a problem with the extender, and you didn't just get a component installed backwards in the preamp?

E49

It's been some months since it happened, but I made sure all of the components were oriented correctly multiple times, and sent photos to the owner who didn't see any that were not oriented correctly. And with the extender I had installed it backwards first and had to redo it (before ever plugging it in, I noticed it was reversed right after I finished soldering), but when I did the cables weren't fully connected, and I didn't notice, and something shorted out. It was the DIYRE one, and they actually sent me a replacement one. I tested the new one on a different 500 unit and it worked fine. So, I know that's no longer the cause.

 

[ccaudle]

the cables weren't fully connected, and I didn't notice, and something shorted out.

Knowing the exact way the extender was incorrect might help predict what failures could have been caused.

 

[kytul88]

This is what I sent DIYRE and they said that could've been the issue. As I was lifting it off, the top part holding the pins into the wires came up and I quickly put it back down. They figured it probably didn't connect back properly or something like that.

 

[ccaudle]

What part of town are you in?

 

[kytul88]

Northeast, Humble/Kingwood/Atascocita area. But I work on the far west side in the Westchase area. So, I can meet all over without any issues.

 

[kytul88]

BUMP. Still need help, if anyone can.

 

[ccaudle]

Sorry, meant to get back to this then I got completely swamped by a problem at work.
What test tools do you have available? I assume DMM, do you also have an oscilloscope?
Did you put in sockets for the op-amps like the assembly guide shows, or solder them directly in?

I printed off a copy of the schematics to review, there are several op-amps and some transistors, usually checking DC values at the pins will get you pretty far in verifying if any component was severely damaged by having e.g. one of the power rails removed, or full power rail applied to an input or output pin when it shouldn't be.

I need to leave work and go eat, but I will write up some starting steps tonight or Saturday to get you started. You can start by checking the power supply voltages to make sure they are within spec, then give the top of each component a light touch to see if any are getting hot. An op-amp with no signal going through should be hard to distinguish from room temperate, so if anything feels noticeably warm make note of it then turn off power to keep from doing more damage.

If nothing seems hot, then measure the voltage at the output pin, inverting input (marked - on the schematic) and non-inverting pin (marked + on the schematic symbol) of each op-amp. With positive and negative power supplies, usually the stages are designed to have 0V at the output with no signal going through, although that may no be strictly true, especially around the mic input stage where the op-amps also have to bias the input transistors. I'll look more closely at the schematics later and check.

One thing which should always be true for op-amps is that the inverting and non-inverting input should be the same voltage, as accurately as a normal voltmeter will show. Any difference between those two input pins is amplified by the open loop gain of the op-amp, so even 1mV difference will cause more than 1V on the output if the op-amp is functioning.

With values for the power supply voltages, and a table of + in, -in, output voltage for each op-amp you can probably get pretty far in determining which components were damaged and which are likely OK.

 

[kytul88]

Yes I do have a DMM, but no Oscilloscope. I was running sine waves out of my computer for testing. And I did use sockets, and swapped the opamps with the ones in my second unit (bought 2, didn't want to start the 2nd build until the first one is finished and working), and there was no change.
I've checked all power points and they're fine.

But to be honest, I was more-so looking for someone I could pay to either fix it, or at least diagnose the issue, that way I can do the fix. I just don't have the time to do all of the diagnosing at the moment.

 

[ccaudle]

I was more-so looking for someone I could pay to either fix it

I understand now, I thought you were looking for someone to teach you how to diagnose faults and learn how the design works.

 

[kytul88]

Yeah, I would want to eventually. Just not now with work, kids, and school piling up a bit.

 

[kytul88]

I understand now, I thought you were looking for someone to teach you how to diagnose faults and learn how the design works.

So, would I be able to bring it to you for repair, or at least a diagnostic? If not, maybe you could write that guide you mentioned and I can try tackling it again myself. Please?

 

[ccaudle]

I have some stuff to do with one of my kids for school this weekend, so I can't do anything hands on in the near term, but my post #9 is a good starting point.
I also do not have a 500 series chassis, that would be needed to power up the module, correct? The extender cable plugs into the chassis, and brings out the backplane connection so you can access the card while still connected to the backplane?