RF punch 160.4 front amp broken

[manninen]

Okay,

did some foolish things and bought amp from the `bay which said to be working.

rear channels indeed seems to be okay but when i put rca into front theres no sound, just ground noise´ish distorded 100hz (about)
maybe i have to take video for more exact sound.

just asking if somebody had similar problem?

amp cover havent been open until now, nothing visible to my eyes.

does anyone have service manual for this amp?

amp looks like this

 

[Perry Babin]

What's the PC number on the board?

 

[manninen]

Pc-0929-c rev c

 

[Perry Babin]

Are both crossover cards set to full range?

 

[manninen]

Sure. I have 2 of these amps. Other works.
On both amps front are more silent than rear channels, front are so silent you can put +100db compression driver behind with out hissing.

Other amp draws 27w idle and broken one only 7watts.

 

[Perry Babin]

The idle current difference couls simply be a different bias setting.

Have you checked the RCA shield grounds on the RCA jacks? They break under the jack.

 

[manninen]

And Steve from rftech sent me service manual.
Very good customer service i have to say for year 1995 amp what this is.

i have to check that other amp too sweep sound on start-up.
check capasitors and biases on both amps

https://dl.dropboxusercontent.com/u/33080121/hifi/SAM_1156.MP4

this is a video about it, noise comes when rca is in

 

[Perry Babin]

I don't watch videos for repairs. It may help someone else.

What's the resistance from the front input RCA shields to the main ground? No RCAs plugged in.

 

[manninen]

Thanks perry for input, your Basic Car Audio Amp Repair link looks good.

Just took both amps to guy which hopefully has tools checking these out.

about bias and idle current, both have never been open, is this normal to amps have so different bias from factory? 22years have change the bias?

 

[manninen]

The idle current difference couls simply be a different bias setting.

Have you checked the RCA shield grounds on the RCA jacks? They break under the jack.

yes, this amp is fixed, grounds broke under rca jacks.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

this needs to get some biasing, any idea how to do it and which specs?

 

[Perry Babin]

This is how I set the bias. You'll need a flash capable device to view it.
http://www.bcae1.com/temp/ausettingbias.swf

 

[manninen]

An externally hosted image should be here but it was not working when we last tested it.

loan this picture from broken 55.2. so turning that potentiometer i´ll mess bias in RF amps? 5-7w per channel seems to be it on these small ones. i had this 27w amp on like 24hours and it was quite warm, maybe 40celsius

 

[Perry Babin]

I don't know how many watts per channel. Getting the outputs to just start conducting should be good enough.

 

[manninen]

Perry, what would you do in this situation? leave it cold or warm it up

 

[Perry Babin]

The bias, for a properly designed amplifier, should not vary significantly, regardless of temperature.

 

[manninen]

So changing bias does not affect to amp temp?

what do you think what makes this difference between these 2 similar amps?
other has broken components inside?

 

[Perry Babin]

Biasing the amp higher will make it run hotter due to increased current and power dissipation in the output transistors.

I don't know.

 

[manninen]

both amps has now same bias, its time to make 4-way active great again.

My friend Legis helped me with setting, daummn that potentiometer is hard to set.
would not ever bolt an amp in subwoofer box, i´ll bet helluva vibration could change the bias amd other stuff.