Refurbing an old school classic Rockford Fosgate Punch200DSM

[Wicks]

Disclaimer: Prepare yourself. Gratuitous amount of amp porn coming up!

I bought the amp used from a friend in 1994 and it was built in 1993 which makes it a lot older then most of you on this forum...

I popped the board out, here's a walk-around:

Pic of the output FET's. IRF540's. Good for 100V and 33A each.

In case you're curious: These conduct alternately from the positive and negative power rail to the speaker outputs.

Pic of the Power Supply FET's. IRFZ40's. Good for 60V and 50A each.

In case you're curious: These pulse the 12-14V from your electrical system through the primary of the power supply toroid transformer.

They help turn DC voltage into AC which the toroid then can use to create a higher voltage AC.

Power Supply Rectifier Diodes. U1610/U1610R. Good for 16A each.

In case you're curious: These "rectify" that AC voltage that has been boosted by the toroid and turn it back into DC (power rails).

One rectifies for the positive rail and one for the negative.

Since its was a good 20 years old I wanted to refurb it since electrolytic caps tend to dry out and degrade with age.....or do they?

I went to Mouser.com and ordered up a bunch of different replacement caps to see which ones I liked best.

The amp was originally built with Nichicon brand caps (which most old school amps were) and they are great caps but it is possible for good caps to go bad after 20 years of intermittent use.

I have access to a nice LCR meter at work. An LCR meter can measure impedance, capacitance and inductance at various frequencies and is very handy in determining whether components meet their specifications or not.

Here are the old Nichicon's (from the power rails) on the LCR:

They're rated at 3300uF so to my complete surprise they are still well within initial specs (+/-20%).

(3mF = 3000uF).

Here's the best available replacement cap from Nichicon since that series of cap is no longer available.

As you can see, brand new, out of the bag and they measure ~2800uF and a slightly higher ESR (Equivalent Series Resistance).

Here's another brand (Cornell Dubilier 3900uF):

Here is a new cap from Panasonic which is rated at a higher base capacitance (3900uF):

You an see it takes a higher rated cap to even come close to that original rating of 3300uF.

Really justifies the saying: "They sure don't make 'em like they used to..."

[Wicks]

Here are the 12V caps at the power input to the amp:

These are what cause that spark when you first connect your power wires to the amp as the caps charge up QUICKLY.

Here is what they measure:

I found some nice Nichicon "MUSE" replacements which are supposed to be great for music applications:

Similar capacitance but much better ESR!

Here's an angle shot with the power rail caps removed. I decided to use the 3800uF Panasonic's as the replacements based on how close their measurements were to the originals and because they make good quality caps.

Looky what I found, a burnt power supply FET. Good thing I decided to refurb some parts.

Smaller caps, various power resistors and 12V input caps replaced:

Lining up the new power supply FET's. ST P75NF75's. Good for 75V and 80A each!

Output FET's yanked:

Output FET's lined up. IRF540's, similar as the originals. 100V and 36A each.

Output FET's soldered:

Refurb'd walk-around:

Hmmm, originally had a red power LED. Red means "bad"........lets swap that for a green one.

[Wicks]

Some new thermal grease on all the FET's:

Back in the chassis:

On the test bench to try it out:

No magic smoke.....we have success!

Here's how she sits currently:

A little trivia for all the new school kids:

The Punch200 was so good in the early 90's that MANY car audio review magazines named it their new Reference Amplifier to test other amps against. One of my favorite amps Rockford Fosgate has ever produced and it started the trend on a lot of new emerging technologies: End-caps to hide your wires. DSM "surface mount" components to make the board smaller, more producible and reliable.

Check out my build log for more upcoming pics of this old school classic.

[TRTC360]

this is awesome

[Kyblack76]

Yes... yes it is.

Very very cool brother WICKS.

Back in the day, that amp was highly thought of, and by some, myself included, still is.

Such a cool addition to your build bro. Great idea. And great execution man!

[Jeremy Perfect]

I had one the 200 and that was a great amp. Just keep going and not get hot.

[boom50cal]

That's too sweet man. Old school gear at it's finest.

[CleanSierra]

I've always had wood for JUST about anything you say because I can accept it as truth. Beautiful work on the amp and bringing her back to life. I remember the old school, it was a good time to be into car audio.

[Nightshade]

What kind of power did you end up getting out of it with the new parts?

[2loud4uboyz]

Wicks you have skills sir. Love what you did to that amp. I Love that amp.