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Old 4th December 2007, 02:38 AM   #1
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Default schematics for older RF amps

Hello amp fixer people....

I'm working on a few dead Punch amps and have contacted Rockford Fosgate through the "customer service and technical support" link on their website, requesting schematics. I hadn't received a response in a weeks time so sent another message a couple days ago. I asked this time if they'd please let me know if as an individual (not a dealer) if I could not be given schematics, etc. (then I'd now to quit asking for them). I've read on this forum (from Perry and others) that schematics are generally sent out in short order so I'm wondering if I'm sending the request to the wrong group or something.

Presently its a Punch 60 DSM that I'm working on. The FETs driving the primary had failed, their gate resistors showed signs of heating. I replaced these parts along with the SOT23 packaged bipolar transistors that drive these FETs and now the supply functions. One channel outputs the negative rail (about -26v) however. I replaced a shorted output FET (a BUZ11) but the problem still exists. I'm guessing the problem lies in the driver module but I don't have a schematic for this one. That makes it all the more difficult to figure out what the problem might be.

Do any of you have a schematic that you'd share for this amp?

I'd also be greatful for any tips you can lend me. I've been designing temperature control circuits for >20yrs but have little experience in the audio field.

Thanks in advance,
17DoubleE
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Old 4th December 2007, 04:28 AM   #2
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As far as I know, the schematics for these amps do not include driver board schematics.

Do the driver boards have transistors on both sides or do they have transistors on one side and resistors on the other?

Rockford has always sent the schematice when I requested them (except for amps that were still in production). They had some server issues. Maybe they're still having problems.
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Old 4th December 2007, 06:28 AM   #3
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Driver boards are available on E-bay from a seller by the name of "dealsbyjason" for like $7.00 each. I know I bought some and they work perfect...hope this helps...
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Old 4th December 2007, 12:13 PM   #4
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The driver boards have active parts on both sides. An older post here about a 200iX has a picture of the same driver board.

This board is marked: PUNCH DSM N-CH DRIVER MODULE PC 0040-B 6-1-93

I'm not certain the problem lies on this module but thought it likely. Perhaps I should remove the working one and solder it into the non-working channel to test this idea..

Buying one for $7 wouldn't be bad either. It would be satisfying to understand and fix this one though.

I do have the schematics for the 100iX and the 200iX. Do you suppose the drive circuitry is the same as on these modules?
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Old 4th December 2007, 01:59 PM   #5
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I don't know if the IX and the DSM circuits are the same. From the components shown on the DSM schematic and considering that they both use all N-channel outputs, I think they are probably very similar.

In the following directory, there are 2 swf files. These show problem components that commonly failed. These are flash files. You can right-click and zoom in. Use the left mouse button to navigate when zoomed in.

I also included schematics for the 200dsm and the 200ix.

http://www.bcot1.com/images/
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Old 4th December 2007, 05:29 PM   #6
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Thank you Perry! The SOT23 transistor in the lower right of the #1 module pic has it's emitter (?) tied to the gate drive resistor. I'l check that part first. The one on my module is marked "3BU" rather than "2AN" as in the pic.

I checked on this website to find out what a "3BU" part is but didn't find it there:

http://www.tkb-4u.com/code/smdcode/indexsmdcode.php

Do you happen to know the part number for these transistors?
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Old 4th December 2007, 05:50 PM   #7
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There were several 3B transistors. It seems like the MMBT918 is the most likely match. If that's the case, the 2A was likely a later revision. The 2A is an MMBT3906. I generally use an MMBTA56 in place of an MMBT3906. Either should be a good sub for the 3B in this application.

Don't forget to check the SMD resistors on the driver board.
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Old 4th December 2007, 11:32 PM   #8
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That's good news for me Perry (the transistor part numbers). I have some MMBTA56 and have access to the MMBT3906 also. I've worked with the A56 (and A06) in many circuits, using them as switches, generally driving them into saturation, etc. In fairly large volumes the company I work for pays about 1.3 cents for these.

Using the diode check mode of my DVM I can't measure a base-emitter voltage on one of the transistors you'd drawn the yellow box around. I wouldn't think the surrounding circuitry should prevent the DVM from forward biasing the junction, or am I not thinking this through correctly? I tried both polarities with the DVM.

I see from the schematic you sent the link for, that the audio input is capacitively coupled to the input of the driver module which further makes me think the problem is on the module.

justonemoreamp: I contacted Jason who sent a link to the older ebay auction for the modules. I confirmed that my module looks like those he has for sale and I plan to buy a couple. It'll still be fun to try fixing this one though.


Thanks to all who've offered information and ideas. I wouldn't have guessed a site existed where such detailed information is exchanged. Awesome!

Bill
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Old 5th December 2007, 12:57 AM   #9
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I think the transistor is probably defective.

If you apply enough solder to the two adjacent legs and heat both at the same time, you can lift them off of the board without removing the transistor completely. You'll have to remove any solder bridges between the legs and the board to check the transistor. For transistors in difficult locations, leaving one leg soldered down makes it easier to get the transistor soldered back in place if it's OK.

These driver boards are generally easy to repair. For some reason, the other driver boards, the ones that had all of the semis on one side gave me fits (technical term).

There's a 68k ohm resistor near the top corner of the board. It usually looks burned when it's defective but you should check it anyway.
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Old 2nd September 2010, 06:05 AM   #10
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I have a schametic for the 60ix .It looks like it has the driver stage on it..not sure though at first glance. my e mail is biglog15@yahoo.com if it will help u I can e mail it. Thanks KIP MCGEE
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