CRUNCH BLX1000D, few questions about repairing this amp.

[djmdp]

Hello, I have this amplifier and power mosfets of digital audio is missing. I don't know what mosfets supposing to be there on places: Q161,Q162,Q171,Q172,Q181,Q182? Is it a half bridge with complementary mosfets p and n channel topology? There's an identical amp - CRUNCH BLX2000D and BOSCHMANN PSX-D1. I thought that this is half bridge topology with n channel mosfets and set there irf540N. Now I don't know that gate driver is still ok,but it looks like complementary driver, no bootstrap, no VS connected to driving circuitry.

[Perry Babin]

Which legs of the high-side FETs are connected to which legs of the low-side FETs?

What is the voltage rating on the rail filter caps?

[djmdp]

So, all middle legs are connected together with the filter inductor leg, first on the left mosfets (Q181 and Q182) has right legs connected to -50V rail, left is gate. Next mosfets (Q171 and Q172) has right legs connected to +50V rail, left is gate.
Next mosfets (Q161 and Q162) has right legs connected to +50V rail, left is gate.
Rails are +50V and -50V.

[Perry Babin]

The two on the negative rail are N-channel FETs. The other 4 are P-channel FETs.

IRF540s and IRF9540s may be the right FETs but ±50v is right at the limit of the FETs.

[djmdp]

So this is complementary power amplifier for 100%? Now I must recheck gate driving, there is square wave of 1V-2V amplitude at -50V DC offset, so N channel seems to be good. I'll check the P channel.

[Perry Babin]

The amplitude must be greater than that. The drive signal is generally 10v and is driven from a 12v supply referenced to each rail (positive and negative).

[djmdp]

Hello, I bought 2*IRF640 and 4*IRF9640 as a power fets. I've done a schematic of my drive board. There's a drive signal on P mosfets with amplitude of 7V, but there's no signal on N mosfet drive. So I need a little help I replaced all transistors on this board, comparator and diodes except three diodes named CR1, CR2, CR3, is it zener diodes? Voltages that I measured (subj. to ground):
IC1A 1 -> -50,4V
IC1A 2 -> -35.2V
IC1A 3 -> -42.9V
Q2 base -> -49.9V
Q2 emmiter -> -50.4V
DRIVE signal -> +14.5V
I don't understand how this circuit generates pulses to N mosfet, what's the role of this comparator here? Please ask, I can measure more voltages. Oh there's a little mistake on the schematic, Q11_1G1 transistor is exactly the same like Q4 - BCX56-16

[Perry Babin]

The comparator is used for over-current protection. When engaged, it drives the emitters of the voltage amplifier/inverter transistors so that the signal from the drive circuit (not the 'drive' indicated in your diagrams) can't drive the transistors 'on'.

The drive signal for the N and P channel FET drive circuits is the same.

The Zener diodes are 1N4742As.

The driver circuit for this amp appears to be in the blue box at the end of the driver board.

This amp is very similar to the JBL BP1200.1. Email me if you want the JBL service manual.
babin_perry@yahoo.com

[djmdp]

Now, when I've got more info, I figured out that probably a/d converter is damaged. On the schematic we can see PWM_0..4V signal, but I also figured out that this a/d converter circuit is supplied by +5V and -5V. 0..4V PWM signal cannot drive Q9 transistor am I right? I think that PWM signal was -5V..5V. That's why the amplifier has been damaged. Schematic of JBL BP 1200.1/600.1 is almost the same. Now I've got to build my own a/d converter ;( blue box.

[Perry Babin]

The LM361 operates off of a +3 and -2v supply, generally. If you remove the diver board, do you get a square wave drive signal to the driver board pads?