Mackie TH-15A

[The Dude]

I would see what the datasheet says.

[lowell]

Also to report back on previous measurements, now that the thing is working. U103 opto has ~+27v on pin1. There is ~1v across the LED. Pins 3/4 are at -170v, and that makes sense because it's saturated and the emitter is tied to HOT ground - -170v. I'm guessing if the FB pin of the PWM isn't pulled down there, it will go into shut-off.

What is U102 TL431. Says it's an adjustable zener of sorts. Couldn't really gather how it works from the datasheet.

[Jazz P Bass]

TL431 is an adjustable voltage regulator.

Adjustable output.

TL431.pdf

[lowell]

Yes I read that. But don't understand how it works. I see that there is a Vref of ~ -2.8.

-28v R119/116 make a 10/1 divider to -2.8v.

Otherwise, C121 is kinda botching it for me. When looking at your pdf, I don't see a cap there. So, Vin is coming from +28 thru R113/114 correct?

[mozwell]

If ambient is (say) 20C, then you have a rise of 35C and 20C
The junction of the diode can typically go to 125C or on some diodes 150C (or so)
I would not be concerned about the temperature rises you are getting.

Good job getting this to work

[lowell]

Thanks Mozwell. I do remember reading, a long time ago, about 25C being room temp and that any heatsink should made to keep this from rising too much. I'll have to brush up on the watts/degrees literature.

Side note: I have some solder (chip quik?) that I bought years ago. But it's not labeled. It's specifically for desoldering SMD components. Melts at a lower temp and stays melted long enough to heat an entire large IC for removal. Can someone please remind me what this type of solder is called?

Finally, I fixed the other broken Mackie Thump in 30 min. Same problem. As always, thanks for the help from all the Ampagees.

[mozwell]

A heatsink is there to stop the transistor or diode getting above its rated maximum junction temperature. The heatsink is (hopefully) sized to give a good safety margin under worst case operating conditions.
If the junction or case of your device is not getting above (say) 80C then you are good to go

If i don't need to keep the surface mount ic, i just run solder along all the legs on both sides of the ic, then as i heat up one side, i can gently lever the ic up. I then heat up the other side & the ic can be easily removed.
Now i get my solder sucker or solder wick & suck up all the solder so i have pads with just a fraction of solder on them. I then put the new ic in place & solder one of the corner legs & then the opposite one. I then go & solder all the remaining legs, carefully inspecting with a magnifying glass or other such device that i have no shorts (I have to account for my "old" eyes not being as good as they once were).

I found this to be an easy way to get rid of a surface mount ic when i don't have proper surface mount rework tools

It goes without saying that you must use the smallest tip possible on your soldering iron

[Jazz P Bass]

Side note: I have some solder (chip quik?) that I bought years ago. But it's not labeled. It's specifically for desoldering SMD components. Melts at a lower temp and stays melted long enough to heat an entire large IC for removal. Can someone please remind me what this type of solder is called?

"Chipquik".

Chip Quik - Chip Quik Alloy (10)

[lowell]

Damn that's pricey!!

[lowell]

This is much more affordable. Will have to give it a try and report back. QuickAlloy Soldering Supply | Product Categories | CyberDocLLC | iPhone and Apple Products Hardware Repair Solutions

[nickb]

This is much more affordable. Will have to give it a try and report back. QuickAlloy Soldering Supply | Product Categories | CyberDocLLC | iPhone and Apple Products Hardware Repair Solutions

U sure?
Chip quick 2.5 ft for $16 i.e $3.46 for 16.5cm
Quick Alloy 16.5 cm for $4

I have also some and have had mixed results. The problem, I think, is that sometimes the alloy does not flow between the pad and the lead leaving a tiny bit of solder that still needs the full temperature to liquefy.

[Shadrock2]

How does Chip Quick work?.
In the past if a unit contained surface mount chips I pretty much just gave up.
Its very appropriate now since this mixer I'm working on has some surface mount stuff.
Or any de-soldering method.

[52 Bill]

How does Chip Quick work?.

Search the forum, I know that we have discussed this a few times before.

Basically, it is an alloy with a low melting point that you add to the existing solder, which then lowers the melting point of the original solder enough that the entire chip stays softened enough to be removed from the board, without having a rework station.

[anwarotti]

Hello Lowell.

sir, i have a mackie thump 15 a ... and i have the same problem you had long time ago ..
i was wondering if you still remember this and how you have done it before ...
would you please let me know what did you do exactly to fix this ..

i had a problem with the input XLR so i took it to an authorized place to change the XLR input and since then im having the same problem you had.. blump blump.. even if im not connecting any input cable intp it,,if i just touch the volume it gives me the blump sound and it feels like there is a huge air sound coming throw... also when i turn off the speaker it hit like a big blump bass ... so what exactly you have done here .. i hope you would see this .

you can send me on my email at anwarotti@gmail.com

let me know if you have any contact to talk directly to you.

thank you

[Enzo]

Hi, please do yourself a favor and not put your email address on the forum. That is a good way to start getting all manner of spam in your in box.

If you took the unit to a qualified service shop and it now has a new problem when you got it home, TAKE IT BACK, a shop should have a shop warranty. Tell them you paid for it to be repaired but it is not yet fully repaired. Give them a chance to correct this.