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Old 6th January 2006, 12:28 AM   #1
240z4u is offline 240z4u  United States
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Default Attempting to fix amplifier, guidance needed please! LONG

I am working on a PSE studio V monoblock. One amp had its outputs shorted with another amps outputs which caused a failiure. The ex owner replaced some components and got it running again to have it die out again 3 months later. It blows the main fuses, and with the dim bulb setup lights up a 100w bulb to full steam.

Here is where I have gotten to so far. Power supply to the driver board is fine, voltage is the same as the undamaged amplifier.

This amp uses two types of outputs, both sanken. Four a1186s, and four C2837s per amp. I used the dim bulb setup and pulled outputs one at a time. I pulled all 4 2837s and still had the bulb light. The first 1186 I removed made the bulb go out and the amp come out of protection. I replaced that 1186 with the NTE correct replacment (yeah I know NTE is frowned upon). The bulb did not light after replacement so I figured I had found one of the dead soldiers.

Here is what has me confused.

When I put inputs in the first three positions back in (2837s) the light lights up. However, if I only leave one output in the far right position the bulb does NOT light. If I move that same output to another location the bulb lights up again.

Does anyone have any ideas as to whats causing this? I do not have a schematic for the amp, just a good working one for reference.

All resistors and diodes are checking out fine. I am still testing the smaller semiconductors that are on the board. Does it seem like I am on the right track?

I am a relative noob, but understand electricity pretty well. I am confident but could use some guidance.

Thanks everyone - Evan
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Old 6th January 2006, 12:37 AM   #2
clem_o is offline clem_o  Philippines
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Evan,

From each of the power output transistors you've taken out, there will be a power resistor of low value (0.1 to 0.4 ohms?) connecting to output of the amplifier. Its possible that one of them is open so that putting the transistor back in that "position" doesn't do anything.

Unfortunately this means that there may be several other problems with the amp that you still have to work out... Specially from the fact that the bulb still lights up!

Cheers!
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Old 6th January 2006, 12:46 AM   #3
240z4u is offline 240z4u  United States
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You are correct, there are .15 ohm resistors inline with each. They are the three leg type and all seem to test out okay. I will pull them from the circut and check again though.

Another oddity that I had forgotten about. With the center leg connected in the circut, and EITHER of the base or emitter being connected = lit bulb. They did not both need to be connected

Its kind of funny because these driver boards do not have very much in the way of components. Im sure its something anybody with alot of experience can fix, but whats the fun and risk of electrocution in that??? haha.

Thanks for your help though, I do not know anyone around my area that I can bounce info off of.

Evan
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Old 6th January 2006, 12:51 AM   #4
clem_o is offline clem_o  Philippines
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Quote:
Originally posted by 240z4u

Another oddity that I had forgotten about. With the center leg connected in the circut, and EITHER of the base or emitter being connected = lit bulb. They did not both need to be connected

Wha? Are you sure your output trannys aren't shorted?

Cheers!

Clem
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Old 6th January 2006, 01:00 AM   #5
240z4u is offline 240z4u  United States
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My meter does NOT indicate that they are shorted. I actually looked online at how to test these properly and they seem fine. Is a diode test only a partial indicator of a messed up output?

My light lit up even when I stuck a new NTE unit in place. Funny thing about the NTE unit is that it now meters out as a bad piece. I am not sure if i cooked it with my soldering iron or what. Its an NTE 36btw. How easy are these to burn with a soldering iron? I use a weller orange plastic soldering station set on 3.

Honestly there is a good chance I am dealing with shorted outputs that are not reacting as I would expect under out of circut testing.

Another question, there are several smaller transistors throughout the design. They do not seem to directly tie into the output transistors though. There are several that are tied to input and several that I am not sure of thier function. I attempted to test them with my transistor tester and they seem good.

Also, if one of the 1186's is still bad, could it cause funky stuff to happen when I am on the other side messing with the 2837s?

Clem, I think when I was testing with one leg disconnected it was with the toasted NTE unit. I ASSumed it was good because it was the newest.

Thanks clem!! - Evan
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Old 6th January 2006, 01:21 AM   #6
clem_o is offline clem_o  Philippines
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Hi Evan,

Diode tests are starting-point indicators, it can diagnose a "definitely dead" unit, but may not be able to indicate a leaky Collector to Emitter path. Use the resistance test of your VOM and set it to the 2Mohm range and test for leakage from C to E (in both polarities). Reading should be "open circuit" at all times.

OTOH it isn't that easy to kill a tranny, your iron should be ok as long as you aren't soldering very near to the body of the transistors.

I really suggest you try to get your hands on a schematic of the amplifier. Trying to find out what's wrong with it without knowledge of the amplifier topology isn't easy at all!

The several small transistors are the input / voltage amplification stages of the power amp. There should be another small transistor mounted on the heatsink near the power transistors - that would be the bias transistor, and if it goes bad (i.e. it is open-circuit) its likely the amplifier will exhibit the symptoms you are describing.

"Also, if one of the 1186's is still bad, could it cause funky stuff to happen when I am on the other side messing with the 2837s?"

Yes, definitely...

Cheers!

Clem
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Old 6th January 2006, 01:25 AM   #7
240z4u is offline 240z4u  United States
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Thanks again clem!

I am going to finish testing all the small components and focus back on the output trannies.

I will also do the resistance test and see whats going on in that situation.

Your help is invaluable, I was kinda getting stuck.

I cannot find a schematic ANYWHERE, and spoke to a guy who knows the owner of PSE and he pretty much said theres no way I can get a schematic. I would hope that is not the case, I would be willing to pay for it even. Ill keep trying though. In the meanwhile, ill try to make some progress.

Thanks alot buddy - Evan
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Old 6th January 2006, 01:30 AM   #8
clem_o is offline clem_o  Philippines
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Best of luck then!

If you have a digital camera, take a pic of the top and bottom of the board and post it... might able to get an idea of what kind of circuit it has, and I'm sure a lot of people on the forum can pitch in and help!

In the meantime, I agree, have a go with the transistors first... (make sure your power supply is fully discharged before attempting to test these!)

Cheers,

Clem
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Old 6th January 2006, 01:32 AM   #9
240z4u is offline 240z4u  United States
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Yeah, discharged. I found that out. I know so well not to mess with charged caps yet I did it anyway. BLAMMO. Bout crapped my drawers. I now have bleeder resistors installed with eyelets so I can pop them on after I unplug the amp.

I will get pictures, The board is in kinda crappy shape, with a couple lifted traces compliments of myself!

You guys are the best - Evan
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Old 6th January 2006, 01:45 AM   #10
240z4u is offline 240z4u  United States
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