Autotek XS 1500.1 problems

[Scanlines]

I'm wondering if anyone here has a schematic, partial or otherwise for this amp.

It came in with the output and power supply fets exploded, replaced those and also replaced the HIP4080.

The amp will power up fine now, but the output fet's (RFP70N06's)will get very hot and audio is way distorted.

+12V and -12 V are present and there is no offset voltage at the spkr terms.

I know that I can get a clean sinewave right through the entire input section to the "fuselinks" where it's fed into
the PWM circuitry. IC2 has been scraped ( ?? ) but my sine wave makes it there to pin 14 and in
an attenuated form to pin 2.
Pin 1 appears to be a sqaure wave modulated by the sine signal. Seems like IC2 is working, but I'm in a quandry.

Any advice or help welcome,

Scan

[Perry Babin]

Are you sure that 70N06s are the correct outputs?

They are only rated for 60v. Most similar amps have more than 60v rails.

Is this the stealth amp with the outputs in the center of the sink?

The symptoms sound like the ones I've seen when the outputs were not compatible. This sometimes happens even if you use the same exact part number.

Confirm that the low side drive is ~10v (p-p). The rising side should have a slope, the falling side should be almost perfectly vertical.

The high side drive should have a similar shape but must drive~10v above the rail voltage feeding the FETs.

If the drive signal doesn't fall fast, suspect the diodes in parallel with the gate resistors. If the drive signals are OK, I'd suspect the outputs.

The IRF3710Z has been a good sub in some of the more finicky amps.

[Scanlines]

Perry;


Good call, I found 2 open parallel gate diodes.

Yes, this is the Stealth with the outputs in the center and the big alumimun "slab" it all bolts to.

It came in with the 70N06's originally. and while it sounds good now, the 70n's are still running pretty hot and I popped one not having it adequately heat sunk while testing. The rail is running at 59.6V . If these guys max out at 60V, perhaps I should upgrade
them to the 3710Z ?

Any idea what the trimmer labelled SE2 does (near the PWM section) ?

Many thanks for the help,

[Perry Babin]

SE2 is the DC offset adjustment.

I have one of these amps and the IRF3710Z was the only transistor I could find to work properly in it. This one is a bit different. It has 68.8v of rail. The 3710Zs run cool. Please note that this is the Z suffix part. The non-Z won't work.

Check the B+ and ground terminals on the amp. Clamp a hex wrench in them and see if you can move them side to side. If they do, tighten the screws. If you don't catch this problem, you'll have the amp return with complaints that it's cutting out.

[Scanlines]

Yeah, I'll check those power terminals before it goes.

I have a Planet Audio Vortex on the bench right now with those same kind of issues only this is coupled by the poor grade of solder used.

I'll try running this Stealth amp with the 70N's and see if I feel comfortable letting the amp leave with those installed.

Do you know where I sample the voltage for the DC off-set adjust?

[Perry Babin]

Red meter probe to the positive speaker terminal. Black meter probe to the negative speaker terminal. Adjust for the lowest DC possible.

[Scanlines]

Thanks Perry;

It worked out great.