This Power amplifier was brought to me stuck in protect and would not pass audio. It is a Chinese amp that is re badged with a few different names. I informed its owner that if the output stage had blown maybe it wasn’t worth the effort and he agreed that if it not something cheap to repair then it was for the best that he got a new one. Output transistors for the Chinese amps can cost a fortune and easily cost more than the amp itself just to rebuild the output stages. Having said that being as these are made down to a cost they can sometimes be something as simple as a bad solder joint.
I pretty much gave up looking for any information on this one straight of the bat and opened it up (Chinese seem not to be very helpful like that).
My first impression isn’t to bad to be honest its not the Ive seen much worse. Yeah its no crown.
The output module on the right looks like a bitch to get to the transistors so I’m hoping that’s not the issue. The out put from the module goes to a header on the power supply board were the protect circuitry is along with the relays that break open when the amp sniffs dc on its outputs to save frying the speakers. With my meter I confirmed there was no dc before the relays and had a quick look at the output by sending a sine 1khz sine was into its input and measuring the terminals connected to the relays.
Both channels looked the same with the obvious crossover distortion on the trailing edge. At this point the amp had no load so more than likely this was the reason for the distortion either way this wouldn’t be the reason for the amp being stuck in protect.
At this point I started reverse engineering the protect circuit. It uses a uPC1237 (equivalent to NTE7100) protection IC more commonly found in Hifi amplifiers and used by many DIY amp builder before it became obsolete. I was hoping this wasn’t dead due to the trouble of having to track one down. So out came the pencil and paper and I started drawing out its circuit hoping to find a dead component.
If you look at the upc1237 datasheet you will notice this is almost identical to the example circuit given. Not a surprise really has that’s how the manufacture expect you to use it. Sadly after measuring everything twice and checking all signals were present it became very clear that this was my culprit.
Well lets try and ignore my shocking photography and pretend that we can see the output relay and the 8pin SIP package that is the upc1237 IC.
If you remember about me saying this IC was used a lot by DIY amp makers well I was once one of them and I decided to see if I had one in my parts bin well after a hours or so I struck lucky. It was a used part that I had scavenged from somewhere in the past. In my frustration of having parts all over the floor I forgot to take a picture but if you can imagine a 8pin Sip package picture here that will work just as well.
I soldered the new part in and also touched up some of the doggy solder joints why I was there this board looked like it had barely seen the solder bath during production.
With this part soldered in I gave the amp a test and it powered straight up and sounded remarkably good. It don’t seem to output its advertised wattage of 1400watts but I’m not sure how they measured that. It maybe capable of this wattage peak like a lot of manufactures seem to sell there wears by these day. Also the crossover distortion seems to have diapered with a 8ohm load.
One last picture
MADE IN THE USA errm ok. Maybe the GDA550 is more of a better way of deciphering its output.