- Audio & Video
Fix Adcom GFA 535 / 545 II - channels not working and/or "thermal protection" light is on
Your amp isn't badly broken!!
The result: on Friday my Adcom GFA 545 II amplifier - which was powering the mid- and woofer-cones of my Paradigm Studio Monitors, stopped playing out of the left channel. And the next day, one of my 535 II amps blew its right channel, and the right-hand "thermal protection" light came on.
When I went to the AudioKarma forums, I found some threads that made my heart sink: according to them, if the fuses on the back of my amps weren't broken, then I had a serious problem in the amp, and I would probably not be able to fix it. I searched around on Google, looking for a second opinion, but I found NO HELP, only bad news.
But you know I wasn'y goint to stop there! Read on to see how to fix your Adcom amp :) for just a few bucks.
Thermal Protection & Secret Fuses in the Adcom GFA Series
The Adcom GFA series has number of safety features built-in, to ensure that neither the amp nor your speakers suffer any serious damage from power issues of both the power supply and power output variety.
Here they are:
- The "AC Power Fuse". this is the only fuse accessible from the outside of the amp. You get at it with a philips-head screwdriver. According to Adcom, this is the only fuse you should mess with.
- "Thermal protection". This thermostat turns the amp off if it gets too hot. Normally, that happens when the speaker impedance is too low or when the volume is too high. Also, it is meant to close (and re-connect the circuit) when the amp cools down. But if you blow on of the internal fuses, the termal protection will remain on, even after the amp is room-temp.
- Secret Fuses: Two fuses on each channel inside the amp offer second and third levels of protection from power-supply problems to the amp. You can only get at these if you open your amp. Of course, Adcom says "don't do this".
Opening the Adcom GFA Series
As if to drive home the point that Adcom does not want you to open their amp, the GFA series is sealed shut with rivets instead of screws. Adcom wants you to send your broken amp to a service contractor. According to the research I did on Google, fixing a broken channel on a GFA amp will cost between $80 and $180, depending on shipping and the price quoted by the service shop or Adcom itself.
But I had a feeling there were more fuses inside the amp (I describe the fuses i found in the list above), so I went to Home Depot with my friend K.V. and purchased a titanium bit for my drill, so I could drill out the rivets on my two Adcom GFA amps. We also got a rivet gun and some 1/8" rivets.
To open the GFA 535 or 545 amps ( and any other Adcom amp with rivets), drill through the rivets with a metal-drilling bit. Use a bit the same size as the little dent in the middle of the rivet. This should be enough to "pop" the rivet apart. If the rivet doesn't pop, use a bit the next size up. Once all the rivets are popped out, you can remove the top, exposing the guts.
I am SO SORRY we forgot to take pictures of our work. But I found a pic of the the insides of the GFA 535 II (to the right, below). Notice the two fuses on the bottom right, and two on the top left. There are the ones I replaced (even though only one was blown).
It was illuminating to see inside. Right off the bat, the 535 II looks like the slightly better-made amp, with individual power transformers for each channel. Otherwise, they looked like the same design and parts - except the 545 II was bigger all around. My 545 was made in 1986, and my 535 in 1990.
Inside the GFA 535 II
Finding and Replacing the Secret Fuses
Inside, it is easy to see that there are two fuses for each channel, nestled right on the circuit boards of both the GFA 535 and GFA 545 amps. They are rated 250v, 4A, and are barrell-shaped (see pic at right).
I bought replacements at Radio Shack, and switched out all four fuses in each amp. In my case, only one fuse was blown. I don't really know what these fuses do, but once I replaced them, and put the amps back together, my amps worked fine :)
Price of fixing Adcom GFA 535 or 545 II: $1.20 if you have the tools, $19.00 if you have to buy the tools
So there you have it! Instead of sending off two amps to Adcom for repair (at a total cost of somewhere between $160 and $360 for both amps), and waiting a month or two to listen to them again, my friend K.V. and I fixed both amps in less than 3 hours, including travel to Home Depot and the Shack. Actual time on the amps was less than 5 minutes of work....TOTAL.
Is this a money-maker for Adcom and the service business, or what?!
The actual cost of fixing these amps was around $1.00 for the fuses (a 4-pack is $1.99) and $0.20 for the rivets used to put both amps back together.
In total, I spent around $19.00: $12.00 for the rivet gun, $1.99 for a box of rivets, and $4.98 for eight fuses.