Repair Soundcraft Sprit Powerstation 1200 Powered Mixer

Note you do not have to remove the handles.  Very handy to keep them on because it is heavy and it gets no lighter in pieces.

Fold the control surface back.
Then slide out the shield.

Inside.  What a monster toroidal transformer.

This is the power amp board.
The silver thing with fins is the heat sink.  You can see the fans behind it (Black).
The round things on the heat sink are the power transistors.  (We assume some are blown to a short circuit condition).




The power transistors are:
MJ15024
MJ15025
Ordered some from Element14

Line No. Order Code Qty Mftr. & Part No. Description RoHS Avail. Unit Price Line Price 1 520184 10 MULTICOMP MK3301/51 INSULATING KIT, MICA TO-3 Yes 3603 $0.788 $7.88 10 in stock for same/next working day delivery 2 9556737 4 ON SEMICONDUCTOR MJ15025G TRANSISTOR, PNP, TO-3 Yes 320 $8.44 $33.76 4 in stock for same/next working day delivery 3 9556729 4 ON SEMICONDUCTOR MJ15024G TRANSISTOR, NPN, TO-3 Yes 298 $8.56 $34.24 4 in stock for same/next working day delivery 4 1271634 10 LITTELFUSE 0218010.MXP FUSE, ANTISURGE, 10A Yes 2527 $0.602 $6.02 10 in stock for same/next working day delivery Goods Subtotal: $81.9081.9

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Shipping Charge:
$0.00
GST:
$8.19
Total:
$90.0990.09

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DEBUGGING
1.  With multimeter on the diode (beep) setting, measured between B-E, B-C, C-E on all the power transisors.  On the left channel all seemed short (both the NPN and the PNP transistors) whereas the right channel did not.
2.  Not knowing the designators of the power transistors, I have arbitarilly labelled them 1 to 16.  (Left channel is 1 to 8).
3.  Pulled out transistor number 1.  MJ14024.  Measured it on its own and blow me over, it's OK. 

4. Measured the characteristics of some of the new and some of the [good] old transistors and there are small differences so as they are all in parallel I
 decided to remove all 8 transistors and replace them with the new ones.

Working down the bottom of the heat sink fins is awkward and also the unit is dusty.  I was worried about dust getting under one of the transistors are degrading the thermal resistance.

Upon closer inspection, the heat sink fins are screwed to the thicker plate to which the transisors are mounted.  Removed these screws and removed the heat sink fins and a thermal gasket.  This made it so much easier to clean and work on. 


Add more  photos here

Soldered some power resistors across the fuse holders for the initial power up.

REF	Type	Description	Quantity	E14	RS	Futurelec
Q
Q1, 2, 3, 4	MJ15024	NPN	4	95567294		MJ15024 in stock $7.90
Q5, 6, 7, 8	MJ15025	PNP TO-3	4	9556737 $8.56 8days		MJ15025 in stock $6.20
Q9, 15, 19	BF422	NPN	3			BF422 In stock 20c ea
Q10, 13, 14, 16	BF423	PNP	4			BF423 In stock 25c
Q11, 22	2SC2240	PNP	2			2sc2240 in stock 10c
Q12, 17, 18	2SA970	PNP	3			2SA970 in stock 10c
Q20	TIP49		1	1467914 Fairchild $0.998 2 days		No stock TIP50 stock $1.10
Q21	MJE5730		1	ON Semi MJE7530G TO220 1260719 $2.68 7 days		No stock
SHIPPING						2 Weeks $7 1 week $30

Equivalents T0-220 PNP 1A 300V MJE5730 300V MJE5731 350V MJE5731A 375V MJE800 NPN Darlington 60V MJE350 PNP 300V TO-226 case MJE4353 PNP TO-220 160V