US AMPS VLX_400

[mike49504]

Im working on this amp and have 19.68 volts on the left channel outputs i removed all the outputs from that channel and still have the 19 volts on the output.


This is what i get on the pads for the outputs


Tip 35
1:19.93
2:37.38
3:19.80


Tip 36

1:19.83
2:-37.38
3:19.87


Any ideas on what to look for?

 

[Perry Babin]

I have absolutely nothing on this amp. If no one else can help, post photos of the output section of the amp and I'll try to help.

 

[nigelwright7557]

Im working on this amp and have 19.68 volts on the left channel outputs i removed all the outputs from that channel and still have the 19 volts on the output.

Any ideas on what to look for?

You have broken the audio feedback loop by removing the output transistors.
Its likely the output then has gone to one rail.

You could feed back the VAS output back into the LTP if you have a schematic to test the driver stage.

 

[mike49504]

Ok I figured it out . Amp had 2 bad mpsa56's and 2 06's and also had a defective resistor.

Amp powers up and plays perfect. Now the fun of putting it back in the heatsink.

I got busy and forgot to buy the Kapton film But i have tons of brand new mica insulators which if i go that route should be fun since there is 116 transistors all together

 

[Perry Babin]

In the future, keep a pointy stick handy. When someone tries to bring one of these into your shop, use the pointy stick to guide them and the amp back through the door.

 

[807tubenut]

In the future, keep a pointy stick handy. When someone tries to bring one of these into your shop, use the pointy stick to guide them and the amp back through the door.

LOL!


You have to love a US amp's to repair it, last time I did one, it had so much thermal past on it, It took a quart of acetone, and like 2 rolls of bounty to clean it all up!

 

[mike49504]

No kidding gotta love mica insulators. Im just gonna order the film instead.

Next thing is i gotta try to fine someone in my area thats willing to air brush the graphics back on it

 

[Dr Zeus]

I just repaired a US Amps amplifier a couple of days ago.... 116 transitors? Are you kidding? Mine only had like 10; but being a one channel amp there wasnt much to break. Fortunately for me it was just bad RCA jacks.

I laughed when I saw "Made in Florida". Odd. An old-time installer said these amps used to be demonstrated as mig welders using a loud input source and shorting the speaker terminals to bare metal. I didnt think TIP35/36 transitors could handle that... Then again it was a crazy ara during which car audio was more of a journey.

 

[807tubenut]

I (with my own eye's) saw a US Amps amp, with a 1kz sine wave, used as a mig welder.

 

[Dr Zeus]

Unfortunate for them, Id trather listen to music than have my eyeballs burn out of their sockets. I give them credit though as one of the rare/neet amps I've worked on.