KA7500bd Pin 1 high??? Brutus BXi2607D

[Perry Babin]

Don't remove them yet. When you check them, measure the resistance from the gate leg to the other two legs for each output. If one reads significantly different than those with the same part number, remove it and check it out of the circuit.

 

[Deadly Sones]

Took a little break from this thing.... now I'm back to it.

Checked over all the Transistors again... they all appear fine. The all give relatively the same readings.

I just don't get it.... any other ideas Perry?

 

[Perry Babin]

What's the DC voltage on all 8 pins of the LM293 on the audio driver board?


Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:

 

[Deadly Sones]

What's the DC voltage on all 8 pins of the LM293 on the audio driver board?

Pin 1: 6.69v
Pin 2: 2.46
Pin 3: 9.79
Pin 4: 0
Pin 5: 1.02
Pin 6: 3.17
Pin 7: 0.168
Pin 8: 12.77

Pretty close to what they were in post 5. Pin 3 is way over... just can't figure out what is driving it that high... there is a zener diode that attaches to pin 11 on the driver board. It has the same voltage across it as pin 3 on the 293... 9.77v. Its board designation is @ D206. Does that voltage seem right?

 

[Deadly Sones]

Oops... just noticed you asked for the "audio driver board".... There is 0.000 v on every pin of the 293 on the audio driver card. There is 0.000v on every pin of the audio driver card except pin 2-1 it has 9.88v. I started to test U2. pin 1 had 0.40v and 2 had 0.126v all the rest 0.000 then pins 1 and 2 had 0.3v on each... then retested and got 0.000v on both, now they read .065v. black lead on transformer secondary center. There is 0.000v on every pin of U3 also.

 

[Perry Babin]

Check Q7, 11, 19 and 22. Check for shorts as well as open junctions.

 

[Deadly Sones]

I'm not completely sure how to check them properly... They have 1D and 2D written on them. I lifted the Q 11 and Q7's back feet. Is there a section in your tutorial that goes over testing these specific type? I'm still looking but not having a whole lot of luck.

 

[Perry Babin]

Click the Basic Transistor Testing link in the sig file below. Find the SMD transistor and read the text next to it. Click the link and fill in the blanks in the form that pops up. Send me or post a screen cap of the filled in form. The instructions are in the pop-up.

 

[Deadly Sones]

Well isn't that just the handiest way to compare and know you covered all the angles. Thanks. I couldn't find that in the tutorial.

They all appear to be good. Any other ideas?

 

[Perry Babin]

It's not in the tutorial.

Yes. They all look OK.

Are you sure that none of the output transistors have any broken legs? Sometimes they break right at the body of the transistor.

If there are no broken legs, can you pull the audio driver board?

 

[Deadly Sones]

I've been over them a couple times but they do have those white insulators over the outside legs. I'm quite certain they are good, but I'll check them again before removing the audio driver board. I've been testing them at the pads. Am I going to attempt to power it up with the audio driver board removed?

 

[Perry Babin]

Yes but before you do, confirm that there is a high value resistor (100k?) connected between the gate and source of the outputs. Without these resistors, you'd risk damaging the outputs.

Does this amp use all N-channel FETs or does it use N and P-channel FETs?

 

[Deadly Sones]

All the inputs are 064N`s. The outputs are both N and P. 640N`s and 9640`s.

The resistors on the output side are 10ohm and 20K. The gate resistors on the input section is 47ohm.

Where should this 100K be located around?

 

[Perry Babin]

The IRFP064Ns and the associated components are the 'power supply' components, not 'input' components.

It appears that there are 10 ohm gate resistors and 100k ohm pulldown resistors. It would be safe to power it up without the driver board.

When you power it up, check the DC voltage on the drains of all of the output transistors. Do any have more than a fraction of a volt of DC?

 

[Deadly Sones]

O.K. Pulled the audio driver board. There is 0.000v dc on every drain of the output fets.

 

[Perry Babin]

Does it still go into protect mode?

What is the DC voltage on leg 3 of one each of the 640s and the 9640s? Confirm that all are the same.

 

[Deadly Sones]

Yes, it is still in protect. No turn on click and no dc voltage on any of the 640 or 9640's. 0.000v on all legs

 

[Perry Babin]

Is the voltage on the LM293 on the power supply board different than it was before you pulled the audio driver board?

 

[Deadly Sones]

No they are all the same... within a couple 0.??v of before it was removed.

 

[Perry Babin]

What's the DC voltage on pin 11 of the power supply driver board?