Gallien Krueger MB150S-III not powering

[vegaluthier]

Hi guys! I bought this GK which has a power problem, the previous owner told me that it used to power on but a power protection in the preamp never allows the amp to sound. It used to power on. I opened, saw some capacitors which were bloited so I changed them, but now it doesn't power at all. Maybe I broke the circuit? How can I repair a smd circuit board? I apprecciate any help!
Thank you very much!

[shortcircuit]

Do the obvious first , double check connections , fuse ?? power source ,power switch, if you haven't already. Here is the schematic
https://elektrotanya.com/gallien-kru.../download.html


PS to be clear it powered on for you, before the cap change ?? And what caps did you change??

[vegaluthier]

I changed main caps, there are 4 of 10000uf x 35V, chequed fuse and power in... But I think I broke some tracks in the circuit board... Its a smd board, I think I need tips to work it properly. Should I solder them with cables to be sure? Perhaps some kind of terminals?

[vegaluthier]

It did power but a circuit protection never let the amp work. Now it doesn't turn on at all

[vegaluthier]

I'll try to be more clear in the explanation, I can't see some tracks that are under the caps to see if there is continuity or not... Thank you for your help and suggestions!

[g1]

When changing bigger caps, it's easy to tear out the vias that connect one side of the board traces to the other side.
You might have to pull the caps again. Look at both sides of the board at the traces that connect to the cap leads. Check with your meter that those points are connected from one side of the board to the other. If they are not, you probably tore out the via. You will have to run fine thin wires through the holes to connect the two sides of the board, then install the caps again without disconnecting those wires. Not fun.
Now, once you get it to power on again, you still have to fix the original fault. This is going to be a complex repair, so be sure you are up for it.

[The Dude]

^^^^^^ What G1 said. Also, look at the old caps you removed. If you see little copper sleeves still soldered to the cap leads, that is a good clue.

[J M Fahey]

Problem is that to begin with this is a *complex* quad rail Class F, G or H amplifier (notice even us experienced Techs aren´t sure even about its *name* ) and then electronic problems are simply not "visible", unless gross such as blown top transistors or ICs, exploded capacitors or scorched burn resistors, most others , say about 85% of them, are *invisible* , meaning a shorted transistor or dead IC look exacly the same as a good one.

So you started by something visible: bulged capacitors, so far so good, but be certain that there are at least other 20 to 40 dead components which are not noticeable.

And which are them? Can we gove you a list so you can replace them?
Short answer: no, because we don´t know without troubleshooting first.

[vegaluthier]

Hey guys... recommended tools? I heard of infrared desoldering or a soldering station. They are expensive tools but perhaps there is no other way to do the job gentle. Someone told me about using a needle on the soldering iron and I tried but it didn't work well. If I got a creative idea to repair this I'll tell and take pictures. Broken Vias only with wire then... Thank you guys!

[g1]

ChipQuik can be helpful for desoldering on difficult/multi-layer boards like this.

[DrGonz78]

+1 on the chip quick. There are certain part removals from circuit boards where the first thing I reach for is the chip quick.

[nevetslab]

ChipQuik can be helpful for desoldering on difficult/multi-layer boards like this.

Are the PCB's in GK's MB150 series Multi-layer? I've only had to service one of them, and did get it back up and running, though what it was, I'd have to dig thru my service notes to find it. The thought of Multi-layer, together with GK's 'standard' PCB layout program use of 10-mil annular rings for exposed solder in the solder-mask stage, together with lead-free solder...........not good bedfollows for a novice to attempt surgery on.

[g1]

Maybe I'm wrong, but I consider/refer to anything more than single-sided as multi-layer. He mentioned tracks he couldn't see under caps and smd so I assumed it is at least double sided.

[Enzo]

To me, mutli-layer means there is a layer or layers within the board, a layer you cannot physically touch without digging a hole in the board. Like that extra slice of bread in a club sandwich. Otherwise we have one sided and two sided boards, both of which are common.

[g1]

Ok. But 'more than one' and 'more than two' are both valid definitions for multi.
I wanted to include every 'more than one' option.