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knil7777 26th September 2012 01:32 AM

Orion 2150GX Repair Help
Okay I'm going to jump in feet first on this thread, first off I have to give a big shout out to Perry Babin. I purchased his "How to" material for repairing amps and just let me say that being an electrical engineer that has been tied to a desk job pushing papers for the past 12 years, it was some of the best how to material I have ever read and has inspired me to start getting back to what got me into electrical engineering in the first place (which is tearing into electronics and being able to fix them). I am currenly batting 4 for 4 on amp repairs. Now that the testimonial is over let me get to the heart of why I jumped on this thread.

My brother has placed the above amp in my hands to work on (the Orion 2150 gx). He told me that he had accidently shorted the power wire to ground and he has had a couple of people look at it (one guy replaced the 4 - 50 volt 3300uF capacitors in the middle of the board since they were swolen but was still not able to get it work, since then it has been siting around for about 15 years and is now on my bench.

I went into what I had learned from Perry's material and started checking the power supply section. None of the transistors were shorted. I moved over to the audio section and found the top channel bank was indicating a short circuit on both banks (the 4 parrallel PNP's and the 4 parallel NPN's). I worked the 8 transistors loose from the clamp and started soldering them off the board one by one until I found 1 out of the 4 NPN transistors to be bad and 1 out of the 4 PNP transistors to be bad. I decided to solder the other 3 NPN's and PNP's back into the board to see if I could power the amp and verify it would play with 3 out of 4 transistors in each bank. I powered the amp through my current limiting resistor (an old headlight) and 10 amp fuse and knew that something else must be wrong as the headlight illuminated and I was only getting around 6.5 volts of the power supply voltage to the amp. I used my O-Scope and saw a good looking square wave coming off the high voltage side of the transformer (although it did have some spikes at the leading edge of the waveform, kind of like an H pattern). I was also getting about + and - 12 volts at the rails (coming off what must be the rectifier near the middle of the board). I also noticed that I had about -10 volts DC on the channel that had the bad NPN and PNP transitor in it. I skimmed this thread and did not see any refernce to have DC voltage on the speaker channels, does anyone have a recommendation since this is my first old school amp. I am in this one just for the thrill of restoring an old amp. I saw the NPN and PNP transistors are still avalible through mouser for about a dollar a piece and I intend to replace each set of 4 on this channel. Also since it has been sitting around for about 15 years I was going to replace the 4 - 50V 3300uF Caps (~$9 a piece through mouser, ouch) and the 2-16V 3300uF Caps (~$5 through mouser). I wanted to get my shopping list of parts completed to save on shipping cost. Thanks in advance for any advice, I see we have some very knoledgable guys on this site and any help will be greatly appreciated. Also, Spoony I got to give you proops on getting this beast of an amp going again, nice work on the fab job for the side plates and good clean looking solder work in side the amp, I am hoping I can have success on this amp, would love to get my streak up to 5 for 5.

knil7777 26th September 2012 02:31 AM

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Tried to attach a pic this time

kevinkr 26th September 2012 03:48 AM

:cop: Moved original post to new Orion thread, old thread has been closed to avoid further confusion.

Old thread here for reference:

knil7777 26th September 2012 04:21 AM

Thanks for moving the thread and sorry for the confusion.

Perry Babin 26th September 2012 04:31 AM

These old amps that have no power supply driver IC cannot be powered up through a limiter. You have to clamp the transistors and rely on the fuse for protection.

You may have defective driver transistors. Check the smaller transistors near the output transistors that failed to confirm that none are leaking and none are shorted.

The emitter of the drivers will be connected to the bases of the output transistors through a low value resistor.

knil7777 26th September 2012 02:25 PM

Thanks, I am currently stuck at my day job, so I will troubleshoot those components this evening. My biggest fear on this amp is that hopefully any additional failed components will be readily available from a distributor like Mouser.

90scaraudio 27th September 2012 03:44 AM

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I tried working on one of these a long time ago and was told to replace all the tantalum caps. (Circled in red) and I cant remember if the trans I circled are CEN-U07 and CEN-U57s. If they are and you need some, I have a handful of each. I also sketched a schematic as best as I could.

Let me know about the transistors:cool:

knil7777 28th September 2012 12:11 AM

Thanks for the feedback everyone. I was finally able to get back to troubleshooting on the orion and started looking at the driver transistors and it looks like the MPSU07 is showing shorted on two legs on the channel that had the blown transistors. From the looks of other threads on this type amp I am guessing this part is pretty much impossible to get these days. 90scaraudio, you wouldn't happen to have any of these 07's and 57's MPSU's laying around also? Is there any good equivalent that I could substitute? Also I went straight from my pyramid power supply through a 15 amp fuse earlier before finding this bad transistor and it immediately blew. If I solder out this bad 07 would it be safe to try and power the amp? I would like to at least hear the other channel play and see the amp power up. Again, thanks everyone for the help so far. I knew going in that finding parts was going to be my biggest hurdle on an amp this old.

knil7777 28th September 2012 12:15 AM

Well, just as I posted that last I looked back at 90scaraudio's post and it looks like that transistor you mentioned is the same part, these have MPSU but I bet that CEN is the equivalent part, if so I am very interested in buying some off of you.

Perry Babin 28th September 2012 01:30 AM

You can remove the drivers from the defective channel and apply power.

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