Rockford Fosgate Type RF X6

seankane · 2012-11-20 9:40 am

Hello I have a RF type RF X6 in for repair. The board number is PC-3757-D.

I powered the amp and it was powering up drawing a little much current but slowly bleeding down to normal draw and staying there. The amp is in protect.

There is no DC on the output terminal and the amp is producing around 90v rail.

I removed the cover. I first replaced U21 and same result powered up in protect. I then noticed a component not looking right on the board. The component was a MC340 64P-5 which is a under voltage sensing circuit.

Leg 1 which is the reset was soldered to a solder bridge bewtween pins 1 and 2 of the LM339D, Leg 2 which is input was soldered to R65 a smd resistor marked 4120, Leg 3 which is ground was soldered to a spot on the board which obviously must be connected to ground but without removing alot of components or having a schematic I have no idea where it goes.

I thought to remove it and power up the amp. I did. The amp now stays powered up even with the remote wire removed. You have to unhook power or ground then it shuts off. It will stay powered up unless you remove the power or ground even if the remote is used to power the amp initially but then unhooked.

I looked a little closer under the magnifying glass and found pin 13 of the LM339 to be burned off of the IC or removed by someone, this pin is OUT4 on the data sheet.

I know the LM339 can shut down the amp for low voltage and thermal protections and I was wondering if it could trip the protect light as well? The board looks to be set up like a BD1000 just a little fancier with TO-247 outputs instead of TO-220. Thats why I suspected U21 upon first thoughts.

I will be replacing the LM339D just wanting some input from anyone who is interested and thinks this is an odd problem. I must fix the LM339D before I can further troubleshoot, and then move on to testing the outputs and such to see if a shorted output is setting the protect light off.

Any help would be great!!!

seankane · 2012-11-20 9:46 am

Here is a pic of the board as well...............

Perry Babin · 2012-11-20 11:09 am

The 339 can't cause the protect LED to light up.

It's likely due to a brief over-current pulse as the amp tries to power up or a defective U18.

seankane · 2012-11-20 11:23 am

OK I replaced the LM339 and the amp powers up and down fine now but still in protect. I found C13 was burned in half which connects pin 7 of U7 and U8 to something.

I am not sure what part number C13 is it is one of the little rectangular capacitor orange in color. The ones around it are marked 104V N0 103.

I will replace U18.

For a future reference just in case I have shorted outputs where can I find a sub for SFH154 and SFH9154 every where I look says obsolete!!!

seankane · 2012-11-20 11:34 am

Do you know the value of C13 or have the schematic??

I replaced U18 the protect light is no longer bright but very dimmly lit now and I hear a buzzing on the board as C13 is removed and its coming from that area. Is there any value I can replace it with for testing??

seankane · 2012-11-20 11:57 am

I found a defective U6 MIC4420 CT replaced it and now the amp powers up goes out of protect and as soon as the protect light goes out the amp starts squeeling and has current draw.

Could this be due to C13 missing?

Perry Babin · 2012-11-20 12:25 pm

It could be part of the problem. It's a 0.1uf tantalum capacitor.

It's also possible that the opto-coupler driving the 4420 was damaged when the driver failed.

seankane · 2012-11-20 12:26 pm

Could the opto coupler cause current draw and squeeling?

Perry Babin · 2012-11-20 12:29 pm

It's possible. Anything in the drive circuit could cause that. Replace the cap (with any 0.1uf or greater cap) to see if it helps.

Don't operate it for long like that. It can cause the outputs to fail.

seankane · 2012-11-20 12:31 pm

I thought the tantalam caps were through hole devices like on the bd1000 and bd1500 these are smd, are they the same value then?

Perry Babin · 2012-11-20 12:43 pm

Tantalum is a type of capacitor similar to an electrolytic but instead if using long aluminum plates, it has an internal structure with a rough surface that produces a very large effective surface area which allows them to produce relatively high capacitance with relatively low ESR in a small package.

If you order replacement tantalums in the same package, be careful when soldering them into the circuit. The negative terminals are sometimes sensitive to heat.

seankane · 2012-11-20 8:55 pm

I put a cap in the place of C13, and changed the opto-coupler U15 the HPCL A2211. No difference power up, protect light goes off, squeeling and current draw. I cant keep the amp powered up but for a second or two so its hard to troubleshoot.

Which resistors disconnect the input and or audio section? Is it R35 and R31 or R32 like the bd1000?

seankane · 2012-11-20 9:09 pm

I disconnected R35 150K resistor and now the amp powers up fine and is not in protect, there is no more current draw or squeeling.

What can I troubleshoot with this disconnected?

Does this resistor disconect the udio circuit or the input circuit?

seankane · 2012-11-20 10:01 pm

Please read post #13 first.

Why do I have full rail voltage on pins 5,7,8 of the other opto-coupler and full rail on all the pins of the MIC4420CT?

The side I replaced the driver and the coupler on does not have rail voltage on any pins but the other side has full rail on the pins mentioned above.

I know this cant be right what do you think???

Perry Babin · 2012-11-21 3:42 am

With R35 out of the circuit, you have no feedback, therefore, the output is going to swing towards one of the rails. Do you have a clean signal on pin 1 of U4?

seankane · 2012-11-21 6:12 am

Almost home now and I will check will this be a square wave or an audio signal I am looking for?

seankane · 2012-11-21 6:28 am

I checked pin1 of U4 and it has a clean signal scope set at 2ms 2v/d.

When I increase the volume, the p/s fets start buzzing. I viewed the gates on the p/s fets and they all have a nice square wave.

Perry Babin · 2012-11-21 11:10 am

Is the triangle waveform on pin 7 of u11 clean?

Is there essentially no DC offset on that pin?

If so and you have a new 6171, replace U17 (don't forget to reinstall R35). Does replacing U17 help?

seankane · 2012-11-21 7:29 pm

I was going to change U17 as that component had been a problem in the past with other amps, but I wanted your opinion first as not to change parts uneeded like I have done in the past you know?

I will check pin 7 of U11 and change U17 then re-install R35 and let you know what becomes of it.

seankane · 2012-11-21 7:39 pm

I cant get a reading on pin 7 of u11 because there is 8.50 vdc on that pin.

Rockford Fosgate Type RF X6

Member

Member

Attachments

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member