earthquake 200dhc-mark2

[RockfordFIx]

I have a 200dhc amp in for repair. I replaced the following blown items.
1. powersupply FETS (12 total)
2. audio out puts (12 total)
3. powersupply caps
4. hip4080
5. tc4424
6. tlc271 (this was potted and burnt in the middle)

amp powers up fine on current.limiter. I have rail voltage on 3 outputs on each side (65v) and around (16v) on the 3 FETS beside the FETS with the rail voltage on each side.
some of the ic's are sanded to prevent seeing the part number or ID. I currently have 0.35 volts DC hm offset and cant correct it. as soon as I adjust the voltage starts going up and down but not higher than 0.8volts. does anyone have ic I'd for the following.
IC6
IC3

 

[Perry Babin]

See attached.

 

[RockfordFIx]

hey perry should all 12 of these IRF3710Z FETS have the same voltage around 65volts? could a defective njm2901 next to the protection circuit cause the inconsistency on all 12 FETS?

 

[Perry Babin]

Only half of the outputs will have rail voltage on their drains. The drains of the others will have rail (65v?) to rail (0v) oscillation.

What sort of inconsistency are you seeing?

Does it produce audio?

 

[RockfordFIx]

I am not to familiar with this amp and was thi king it acted similar to the rockford bd series for rail voltages/oscillating. but I realized this amp doesnt have a negative rail voltage. havent put audio through it. was considered with the high DC offset voltage on speaker terminals.

 

[Perry Babin]

Both speaker terminals will be at 1/2 of rail voltage when it's working normally.

 

[RockfordFIx]

this what a 60hz wave form looks like on the speaker terminals.

 

[Perry Babin]

I see the problem, your scope is upside down.

With the same input, post the scope images on pins 5, 6 and 7 of the 4080. with the following settings.

DC coupling
5v/div for all
5us timebase for pins 5 and 6
2ms for pin 7
set the ground reference to the center line on the scope

 

[RockfordFIx]

no I was actually working on the amp while standing on my head. ha

I was able to get a square wave on pin 5 before my scope ground cam loose and touched pin 11,12,13,14 area. no the amp is blinking protection. I guessing I damaged the 4080 ic. I will order a few more today along with njm2901 ic's that i suspect is culprit.

 

[RockfordFIx]

Pin 5

 

[RockfordFIx]

Pin 6

 

[RockfordFIx]

Pin 7 had increase input signal to see waveform

 

[Perry Babin]

Are you using the IRF3710Z from an authorized distributor?

 

[RockfordFIx]

Yes they are irf3710z from mouser

 

[Perry Babin]

Short pins 9 and 8 of IC2. What does the signal on pin 7 look like?

 

[RockfordFIx]

Signal goes flat baseline. If I start to turn the gain up too high I can here a slight popping or arching.

 

[Perry Babin]

I don't know what flat baseline is.

Adjust the level at the signal source, not with the gain.

 

[RockfordFIx]

If I short pins 8 and 9 the signal goes or waveform stops

 

[RockfordFIx]

Should I pull pin 9 on ic2 and check out put signal

 

[Perry Babin]

The signal goes? Do you still have 6v of DC? Did you try increasing the signal from the source?

Do you still have a square wave on pin 5?