What did I do?

[Ricky1]

Well hello! I'm a new guy looking for some help, since I've never done PCB work before.
I'm not sure what type of fault I'm looking for, so I'll just describe the problem, I guess. I was using a mid-80s MCS amplifier in a DIY stereo with the amp and speakers all in one big box. Sort of a boombox on roids.
The amp has three separate but connected boards: power board, equalizer board and a control board with all the buttons and switches on it. I was testing the rig and it was sounding awesome when I accidentally dropped the EQ board on the power board's heatsink, which is aluminum. The fall was only an inch or two, not great enough to damage the board.
There was a ton of snapping and popping once it hit--probably because nothing was grounded--and when powered back on, the audio could be heard through any input no matter which was used, (though it now sounds like a very, very distant radio station with a ton of static) and literally nothing works. I can't change the input, or turn up the volume, nothing--even the LEDs on the boards won't power on.
I checked, and there's no obvious damage, like fire or melting silicon, so I don't even know where to look. I do have a multimeter and a soldering iron, but I've never done repair before and don't know where to start. Any help would be very greatly appreciated!

 

[(*steve*)]

You have possibly caused multiple faults.

From the way you describe the output, I would think that the output transistors are dead, but it may also be the power supply or many other parts of the amplifier.

You may be in for a learning experience.

Do you have a multimeter, and do you know how to use it?

Is there any mains wiring inside this thing and are you confident you can keep well away from it (remember that maybe half of the power supply may be live)?

How much time, persistence, and patience do you have?

edit: Oh, and welcome to Electronics Point.

 

[Ricky1]

Well, I've got a multimeter, but to be honest I only know the very basics. I'm more than willing to learn, though! There's some mains wiring, if that means the power supply connection, lol. If that's the case, it should be easy to avoid, it's honking big and separate from the boards themselves.
I've been wanting to learn about PCBs for a while, and this particular setup looks fairly easy to fix, because of its age. The one problem I've already been warned about is that I'll have no schematics, is that a huge barrier?

Thanks so much, I didn't know who to go to!

 

[(*steve*)]

Perhaps you can take a few pictures and post them. We should be able to see pretty quickly if it has a switchmode power supply or a regular transformer, rectifier, and filter capacitors. The later is far less likely to bite (or bite so hard).

Then we can talk about using a multimeter.

 

[Ricky1]

Perhaps you can take a few pictures and post them. We should be able to see pretty quickly if it has a switchmode power supply or a regular transformer, rectifier, and filter capacitors. The later is far less likely to bite (or bite so hard).

Then we can talk about using a multimeter.

I'm not sure if you want pictures of all 3 boards, so I just took one of the power board+power supply. Here you go:

Thanks so much for your help!

 

[CocaCola]

I'm not sure if you want pictures of all 3 boards, so I just took one of the power board+power supply. Here you go!

You are going to need much more 'zoomed' into detail pictures than that if you want anyone to even begin to diagnose anything... Take 4 or 6 individual pictures of that board in sections...

 

[Ricky1]

You are going to need much more 'zoomed' into detail pictures than that if you want anyone to even begin to diagnose anything... Take 4 or 6 individual pictures of that board in sections...

Thanks, CocaCola, that makes sense, but Steve specifically said he wanted to identify what type of power supply we're dealing with. I figured that he'd probably want to see the full board for that....

There's nothing obviously damaged (no blown capacitors, no smoke, no smells, no sparks or fires), so I think I'm looking at testing individual components, rather than trying to get some poor, but decent soul to pore over blurry pictures on the internet.
I guess right now we're just trying to determine if that's a safe thing for me to do... Based on my past performance, I think I'll need to be more cautious second time around.

 

[CocaCola]

Thanks, CocaCola, that makes sense, but Steve specifically said he wanted to identify what type of power supply we're dealing with.

Well that is obvious from the picture you posted But it would still be nice to see closer pics to progress further...

 

[Ricky1]

Well that is obvious from the picture you posted But it would still be nice to see closer pics to progress further...

Alright, fair enough! I'm heading off to bed now, but tomorrow I'll get a few decent close-ups. Fair warning, though, my camera's not great, and there's a couple of different boards, so there might end up being a lot of pictures.

Thanks for the interest, it's encouraging.

 

[(*steve*)]

Yeah, you have a standard linear power supply. The output of that transformer will be rectified and filtered giving you a DC rail.

This means you need to keep away from the primary side of the transformer and the power switch, but most of that should be insulated and hard to accidentally touch.

In short, it's easier to avoid being killed

As Coca Cola mentions, we now need to see more of the detail.

Perhaps a shot of this board from the other direction so we can see a little of what is on the large heatsink, and try to fill the image with the board. If you're reducing the size of the image, crop first if required, then trim to about this size (1024x768).

Do the same for the other boards (both sides would be good) and tell us which one fell on the main board, and which side was down at the time (if you recall).

We may need to see further images with closeups of various sections as well. but unless you can see anything suspicious, don't worry too much for now.

If you can read the part numbers off the devices on the heatsink it will help us too.

 

[Ricky1]

The boards

Hey, sorry it's taken so long, especially considering how kind you've all been!

I managed to get those pictures, and tried to make them large enough to make out, so here goes:

Power board:

(sorry I couldn't really get it all in one picture...)

Main board:

Sorry for the low quality, this was part of a larger picture...

EQ board:

I tried to make this one large, it was the one that fell on the heatsink. The bottom of the left side fell on the heatsink, but I'm not sure that matters, since they seem to be bridged in the center.

The heat sink is attached to the power board and has some stuff that I can't identify confused attached to it:

A close-up of the unidentifiable stuff:

I looked at the pictures as I was uploading them, and I'm actually not sure that all of the "unidentifiable things" are identical, but they are very similar in size, color, and etc.—the numbers don't seem to match on all of them... if that's a problem, I can get the numbers on each piece.

Again, thank you guys so much for your help so far, it's great to not be alone on this, since I have no idea what I'm doing.

 

[Ricky1]

Just bumping this up since it's been a few days.

 

[Raven Luni]

Have got got pics of the undersides as well?

If you dropped the eq onto a heatsink, thats most likely where the damage is and would account for the poor sound. Theres no reason it shold affect the controller unless the output from the damaged eq is confusing the logic somewhere. Do you get a visible display if you disconnect it?

 

[jackorocko]

The output transistors are isolated from the heatsink. Can't really see how they would be damaged. I'd start with the board you dropped on the heatsink as well.

 

[Ricky1]

Have got got pics of the undersides as well?

If you dropped the eq onto a heatsink, thats most likely where the damage is and would account for the poor sound. Theres no reason it shold affect the controller unless the output from the damaged eq is confusing the logic somewhere. Do you get a visible display if you disconnect it?

I'll get some pictures of the EQ underside tonight. I was kind of thinking I should do undersides, but wasn't really certain. I also agree that the EQ board is probably the best place to start.

I'm not sure that I adequately explained the problem I'm having: I do get sound (poor quality, as mentioned), but the controller is also non-functioning. Each board is connected to the other, and the EQ board is wired straight to the control board, which leads me to believe that I probably spiked the control board.
In my head, it seems logical to think that if I killed the EQ board, I'd be able to use the controller, but probably not get audio to the speakers. However, as I've mentioned, I really don't know a damn thing about board-level repair, so I could be totally off base.

Again, thanks for putting up with an idiot that doesn't know what he's doing.

EDIT: What do you mean by "visible display?" I haven't tried disconnecting the EQ board yet, let me try and see what happens.

 

[Ricky1]

EDIT: What do you mean by "visible display?" I haven't tried disconnecting the EQ board yet, let me try and see what happens.

I tried disconnecting the EQ board, the controller still doesn't function, so... It may be a moot point, but I took a couple pictures of the rear of the EQ board. I also have some of the control board, but I'll wait on your verdict to upload those.

First side (the one that fell on the heatsink):

Second side:

 

[alfa88]

I hate to ask the obvious but have you checked the fuses?

 

[Ricky1]

I hate to ask the obvious but have you checked the fuses?

No, don't worry, if you treat me like an idiot, you're probably being too nice.

I did run the fuses with my multimeter on ohms setting, and got no resistance. I was under the impression that was the way you test fuses, but after googling around, apparently testing with a battery and a light bulb is the preferable way. Is this true? And if so, is there anything I should know before attempting?

 

[(*steve*)]

No, with a multimeter is the correct way. One probe on each end, the meter should read 0 or a very small number.

Note that some meters real 0L when disconnected, this is not 0 and if it doesn't change when you connect the fuse, it means the fuse has blown.

 

[Ricky1]

No, with a multimeter is the correct way. One probe on each end, the meter should read 0 or a very small number.

Note that some meters real 0L when disconnected, this is not 0 and if it doesn't change when you connect the fuse, it means the fuse has blown.

Okay, good, I did it correctly. With that in mind, what should I check next?