Protection circuit on Hifonics Atlantis - diyAudio
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Old 17th June 2006, 10:33 PM   #1
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Default Protection circuit on Hifonics Atlantis

Would a faulty diode/diodes prevent a protection circuit from resetting? I was using this old school amp bridged into 4 ohms. It went into protect mode and has stayed. If not diodes, what else could be a possible culprit? Thanks!
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Old 17th June 2006, 11:23 PM   #2
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It's likely that the output transistors failed. That's the most common cause for an amplifier to go into protection.
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Old 16th July 2006, 02:26 AM   #3
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Thanks Perry! What is the correct way to check outputs with a DMM? If the output transistors are OK, what would be the next logical step?

Thanks!
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Old 16th July 2006, 03:14 AM   #4
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With no power applied to the amp, set your meter to ohms and measure the resistance between the terminals of the output transistors. You should find none that have anything close to zero ohms between any of the terminals. If you find one or more that have ~0 ohms between therminals, they need to be removed from the circuit and checked. If you have several in parallel, it may seem as though the entire group is shorted but generally one fails and the others are OK. Of course, when you have one defective transistor in a group of parallel transistors, you must replace all of the transistors in that group.

Open or broken emitter resistors can cause an amp to go into protect. If you don't find any shorted outputs, make sure there are no broken terminals on the emitter resistors.
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Old 29th July 2006, 01:34 AM   #5
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On each side of the board is an array of three ST 9731 TIP35Cs and three ST 9740 TIP36Cs. Readings between pins 1 and 3 are the same on all 12. Readings between pins 2 and 3 are the same on 9, but ZERO on one trio of TIP36Cs. So, is it safe to assume they are in parallel and one or more of them has failed?

Also, which resistors are the emitter resistors?

Thanks!
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Old 29th July 2006, 02:14 AM   #6
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You're correct. At least one of the 3 has failed.

They are in parallel. All 3 must be replaced even if only one is shorted. However, if you have only one shorted, you can pull only the shorted one leaving the other two. This will allow you to do low level testing to determine if there are other problems. Re-clamp the transistors down to the sink before applying power. Insert a small fuse (15 amps or less) in the B+ line when you power up the amp. If the amp plays as it should, replace the three transistors. I'd also recommend replacing the other 3 transistors (TIP35C) in that channel but that's up to you.

The part numbers are TIP35C/TIP36C. The 'ST' is the manufacturer. The 4 digit number is the year/week of production.

The emitter resistors are directly connected to the third leg of the output transistors.
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Old 29th July 2006, 02:29 AM   #7
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Thanks, Perry! Hopefully I can work it into my weekend to do as you suggested and get this bad boy checked out.
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Old 31st July 2006, 12:33 AM   #8
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I pulled the TIP36Cs from the board. One has no continuity between pins 2 and 3. Emitter resistors seem to be OK.
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Old 6th August 2006, 01:18 AM   #9
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Ordered TIP35Cs and TIP36Cs from Digi-Key. Replaced them on the board and amp works like a beast. This is a very decent old school amp. Made just after the Zed Hifonics amps. Must be pretty obscure as I can't find a lot of info about it. It's the "American Warrior" Series Atlantis X. It has "175x2" on the sink, and says it's 1 ohm stable in big letters. I've found differing figures for ratings, both in 2 channel mode and bridged. Someone on another forum said it may be capable of 1000 watts RMS bridged, but I have my doubts. I would like to know about proper fusing, etc. If anyone has any info, or knows where I can get some, I would appreciate it. And thanks for the help.
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