Hifonics XX Chaos

[mike49504]

With black probe on the ground terminal and red probe on the rca ground shield i get 0.987K ohms.

With amp powerd up i get 13.27 volts on the rca ground shields.

Any idea where to start checking?

 

[joesch1999]

yeah sounds like one of the output tansistors is shorted

 

[mike49504]

How can it be a shorted output when there is 0 volts on the outputs and the voltage is on the RCA shields?

 

[joesch1999]

sorry didn't notice rca shields, same voltage as the input, sounds like a bad zener did you check them?

 

[Perry Babin]

What's the resistance from the B+ connector to the RCA shields?

Check this with no power applied.

 

[mike49504]

0.489 M ohms From B+ to RCA Shields

 

[Perry Babin]

If you ground the RCAs, does the current draw increase?

What's the resistance between the RCA shields and the non-bridging speaker terminals?

 

[mike49504]

0.4 ohms from rca shield to non-bridging speaker terminal.

If i try to ground out the rca shields Amp draws 60 + amps of current .

Now since i tryed that the amp idles high now around 10 amps.

 

[Perry Babin]

You should be working through a limiter.

Do you still have 0 ohms between the RCA shield and the non-bridging speaker terminals?

You may have an intermittently shorted transformer. Measure the resistance from the B+ terminal to the RCA shield while twisting the transformer. Does the resistance ever drop?

 

[mike49504]

from non briding speaker terminal to rca shield nw i havw 4 ohms.

When twisting the transformer i can get it to drop down to 0.8 ohms

 

[Perry Babin]

0.8 ohms from the shields to the B+ terminal means you have an intermittently shorted transformer. You'll have to find the short.

You may have also burned a trace earlier. Look for that also.

 

[mike49504]

So when i find the short do i use goop or what would i use to cover the windings if there are any that the coating has come off of?

 

[Perry Babin]

Generally, the shorts are at the point where the terminal windings meet the rest of the windings. If that's the case here and the short is where the terminal winding goes under the transformer, insert an insulator (cardboard, fishpaper, kapton...) covered in Goop. That will prevent it from shorting there again.

If the windings have burned the insulation off, post photos.

 

[mike49504]

so should i unsolder 1 side of it or the whole thing and see where the shorts at?

 

[Perry Babin]

No. That generally breaks the connection and makes it much more difficult to find.

Do you have a 2 ohm current limiting resistor?

 

[mike49504]

I can pick one up tommrow all i have right now is a 1ohm 25 watt

 

[Perry Babin]

That's good enough if it's a wirewound resistor but you'll have to make sure that you don't allow current to be drawn through it for very long because it will overheat and fail.

Disconnect everything from the amp. Connect the limiting resistor in series with the B+ terminal. Connect the ground wire from the power supply to one of the non-bridging speaker terminals. Twist the transformer. It should spark when the short makes/breaks contact. You may have dim the lights to see it. Find where it's sparking and insulate it.

 

[mike49504]

Ok back to this amp again I cant find the short in the transformer..

From B+ to rca shield should the meter read OL ??

Cause from B+ to rca shield i have 0.3 ohms

 

[Perry Babin]

For most amps, you'll read very high resistance (maybe high enough to read OL) between the RCA shield and the B+. It should definitely not read 0.3 ohms. If you connect your meter between the B+ and shields and twist the transformer, does the resistance ever change?

 

[mike49504]

I twisted it and can get 35 mega ohms from B+ to rca shield .

Voltage on the RCA shields now is 0.02 volts..

but if i bump the amp even lightly the voltage spikes back up to 13.8 volts