Rhino RHE161400 power amplifier repair

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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).

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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.

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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.

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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.

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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

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MADE IN THE USA errm ok. Maybe the GDA550 is more of a better way of deciphering its output.

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Repairing a O2R Digital mixer

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This O2R turned up with dead channels and a few weird problems. Ignoring the few weird problems for now I took it apart looking for the obvious. (by the way these are a pain to get to the boards for the encoders)

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You can now see the ADC board responsible for converting the analog signals into digital. This board uses AK-5390VP that is also equivalent to the CS5390 ADC chips.

On inspection of the boards I found this.

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The desk as obviously taken a knock at some point and the PCB has cracked. After removing the board the track side also had obvious damage and a quick test with the multimeter confirmed no continuity for a few of the tracks. This kinda explained why most of the effected channels were on one side of the desk.

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This isn’t a very good picture I know but if you look closely you can see that the tracks carrying the digital signals from the ADC chips as the tail end of the crack going through them.

With some very tedious soldering and gluing of wires I eventually restored continuity to all the broken tracks.

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I also bridge the ground plane to restore ground to the far side of the PCB. If this was necessary Ive no Idea.

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Well after all this I was hoping that the channels would all just come back life but as it is with these this its never that easy is it.

Stereo pairs 21 and 22 and pair 23 and 24 still did not work. Due to each pair sharing a ADC I decided that maybe the these had gone bad and pulled out the oscilloscope and the AK-5390VP datasheet . The signal going into the chips was fine but the outputs were completely dead. I removed these chips and fitted sockets waiting for replacements to come. The desk is now useable but missing the mentioned channels why I try and obtain these chips from a reliable source.

A bit of a update but I have also now confirmed these chips dead as I borrowed one from a working channel to check so sadly I may have to resort to china for parts. Parts for china can be a bit sketchy as they like to make a lot of fake chips that are no longer in production. Most of the time just removing the number off a similar part and selling it as something else.

First blog post hope Ive got this right

Ive started this blog to provide information and inspire other people with the things that I do. Well all being hopeful.

I been repairing electronics for a very long time and with that comes building and hacking inevitably. This is going not only to be a place that I can use as reference but also to document some of the things I do for others to use.

Well hopefully I can keep up to date with what I’m doing and keep this blog rolling. The first few post probably wont be much apart from a look at some amps that have been in for repair as I try and get my head around this blogging thing.

Cheers Kris.