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Old 1st January 2013, 01:06 PM   #1
WoutRam is offline WoutRam  Netherlands
diyAudio Member
Join Date: Nov 2010
Default Hifonics XX-Colossus; broken power supply

One of the SPS Fets (Q17; IRPF064N) is destroyed. The question is what caused it to fail!?

One of the outputs of the SPS PWM IC, KA7500c pin 9 (= connector pin 9) produces quite a spike shortly after going to zero, see picture I
The second output, KA7500C pin 10 (= connector pin 8) doesn´t, see picture II.
This spike is likely high enough to cause the drivers Q7/Q8 and Q7C/Q8C to produce a spike on their output as well.
Picture III shows the voltage on the output of the Q7/Q8 driver output (large spike)
Picture IV shows the voltage on the output of the Q7A/Q8A driver output
Picture V shows the voltage on the output of the Q7C/Q8C driver output (smaller spike)
Picture VI shows the voltage on the output of the Q7B/Q8B driver output

Oscilloscope settings for all 6 pictures:
vertical : 0 volt level at +1 division
vertical : 2 V / division
horizontal : 5 usec / div

Are these spikes likely to be caused by:
- a failure of the PWM IC, the KA7500C?
- poor decoupling, so a broken decoupling capacitor, on the
Vsupply line of the KA7500C?
- any other reason?
Any suggestion is very welcome!!

Does someone happen to have the schematics of the small SPS PWM controller board (p.no. E08-015-90 2004.05 rev.0), the one with the SMD components, and amongst others the KA7500C, on it?

I figured out part of the schematics, mainly the SPS part, from the 2 PWM outputs of the KA7500C up to the transformers; see enclosed schematics ¨SPS XX-Colossus¨

What is the use of D28 and D29?
(I am not sure if one is a zener-diode and the other one a regular
diode; I cannot read the type numbers). I am really puzzled.
They apparently also limit the voltage on the gates of the 4 x 4 = 16 SPS
FETs to a maximum of +8,5V, see pictures III, IV, V, VI.
However, these FETs can withstand a Vgs = 20V.

Any help in solving this puzzle is highly appreciated!
Attached Images
File Type: jpg I (Upin9).JPG (460.1 KB, 127 views)
File Type: jpg II (Upin8).JPG (361.5 KB, 114 views)
File Type: jpg III (UQ7Q8).JPG (458.3 KB, 112 views)
File Type: jpg IV (UQ7AQ8A).JPG (460.7 KB, 107 views)
File Type: jpg V (UQ7CQ8C).JPG (456.0 KB, 104 views)
File Type: jpg VI (UQ7BQ8B).JPG (474.0 KB, 11 views)
File Type: jpg PowerSupply Hifonics XX-Colossus.jpg (386.7 KB, 54 views)
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Old 1st January 2013, 03:48 PM   #2
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
The diodes are used to clamp spikes on the drains of the FETs. When the spike exceeds the zener voltage plus the forward voltage of the 1N4148 plus the threshold voltage of the FET, the FET switches on to clamp the spike. The problem here is that it's poorly implemented. It fights the pull-down transistor so it doesn't work well. Rockford does it properly and lets the diode array drive the base of the drivers where the diodes only have to fight the pull-down resistor on the driver IC.

Post a photo of the driver board and I'll see if I have anything close.
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Old 3rd January 2013, 11:35 AM   #3
WoutRam is offline WoutRam  Netherlands
diyAudio Member
Join Date: Nov 2010
Enclosed a picture of the SPS PWM controller board (p.no. E08-015-90 2004.05 rev.0).
Attached Images
File Type: jpg Control board Colossus.JPG (574.9 KB, 75 views)
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Old 16th September 2013, 09:24 AM   #4
diyAudio Member
Join Date: Sep 2013
Hy,i have a hifonics gx4000d and the driver board for the output fet's just broke,and there are two 8 pin ic's that have no serial number.Could anyone help me?Thanks!
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