Mackie SWA1501 power amp/psu blown up

[blindboybenton]

Hello
This one is doing my head in.
Customer brings it in with 2 blown fuses and stated that he has changed the fuses they blew straight away
srs1501_AMP_board.pdf

Checked it out Loads of s/c and o/c parts changed
I have changed all of the transistors/fets on the heatsink
Q19/Q14/Q17/Q12/Q15/Q2/Q4 and U1 ( changed to be sure )
D26 to D29
R17/R16/R31/R32/R22
There was a couple of burnt out tracks. All repaired with point to point wired
All the above were blown and replaced with the correct part and part no
Went around the board with meter lifting and checking all resistor/diodes etc
At switch on via Lamp limiter no excess current draw

All voltages measured with lamp limiter in use

On speaker output -19v
15v +/- are correct
25v +/- are correct but at point of R13 to D6 1.8v +
D16-D15 LED's are ok and on

U1 pin 1 and 2 have -19v
U1 pin 15v+
On page 2 of map they show psu, #1 #2 measuring across these points 19v
Measuring across C10 129v
This one is trying my experience and skill
I have read what i can from this forum

Im struggling to get my pc to correctly link up the schematic
Link below will take you too the download site
https://www.elektrotanya.com/mackie_.../download.html

any advice

BBB

[Jazz P Bass]

Can you 'zip' that schematic & reload it?

[Enzo]

And let us be clear what we are working on. Your thread title is about a SWA1501 but your pdf link was names SRS1501. The SRS and SWA amps are not the same.

[blindboybenton]

When i went looking for the schematic i downloaded a few versions all labelled as SWA1501 but SRS1501 kept coming up, checking the amp along side this the versions seamed to be the same

Just checked the paper copies i printed out. they say SRS1501 in bottom right hand corner, But also stating its a SWA1501 service manual

[nickb]

I see the number on the PCB 36963 ties in with the dwg so I guess that is a good thing. I know nothing of the SWA/SRS differences.

So assuming we have a match take a look at the voltages on U3 pin 7,8, & 9. I'd expect to see pin 7 at about -12V or so based on the measurements above. If that is OK I'd be looking for a problem with Q8, Q16 or Q18 and/or associated components.

[Enzo]

The photo shows what looks like an SWA1501 to me. God knows I have repaired enough of them.

[blindboybenton]

Please share your experience Enzo. This amp has driven me to drink today.🤠

[blindboybenton]

Thanks Nick. I will check it out in morning

[Enzo]

There is no quick trick, they blow up, you fix them. I find it is simpler to go around the two rectangular holes and just test every semiconductor there.

You replaced R16,17, but not Q5? How could those two resistors burn up without Q5 being involved?

[Jazz P Bass]

So, where is the 'zipped' file?

[blindboybenton]

I had closed for the day at that point. I can't seem to get my damn old pc to work on this, i use linux
i will try and get it up later, on my 1st post there is a link too where the i downloaded it
Thanks
BBB

[blindboybenton]

I had replaced Q5 i just didnt list it in first post. i had changed the parts a few days earlier. and my old memory had failed me

Thanks
BBB