Need Help With Power Acoustik LT-980/2 Amp

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Hey Everyone, Ryan here im new to the forum with hopes that this will become my new audio help HQ!

Well, lets get to the point shall we, I have an Power Acoustik LT-980/2 Amplifier. A pretty decent amp In My Own Oppinon, and cheap. Unfourtunately they stopped manufactoring this amp a couple years ago, and mine is not working. I bought this amp on Ebay and it supposedly worked when it was shipped out; or so the guy who sold me it says. After a few Emails and phone calls i got my money back, and he doesnt want the amp back, because well... who wants a broken amp!? So its my goal to Fix it! i have another in the mail soon so i cant complain too much but id really like to get it working. :dead:

I also have another quick question! How do you go about Chargeing a Capacitor Correctly? A Link to a Tutorial would be Great! Thanks!

So here are the symptoms.

:att'n: ~For the record, My Connections are Great, Grounded Twice, 20V Capacitor, 4 Gauge Wire From Cap, 4 Guage From Bat, and 2 6 Guage wires from Chasis. So that being said, and seeing as this is the only amp i own that wont work correctly in my vehicle... Its not my wireing, or Car.

1. I turn the amplifier on and it goes into Fault Protection mode and than flickers back to the power-on state for a split second then repeat!

2. I have opened the Amplifier and there are No burnt traces of Components that i can see. although i will say there is One Set of Mosfets and what looks like a smaller chip with a wavey sign below it on the bread board ( im guessing its a resistor of sorts?) that have a bit of a rust colored discoloration on them.

3. This particular board is used for not only one amp. Or so i "think" there are component spots that are missing components and solder, so this is why i mention this.

4. I can get power from a Fuse slot or the Power Connection to "I Think" every spot and component on the board. All of the previous is true, in the Exception that once again this board is used for many diffrent amplifiers and there is a 25 Amp fuse that only goes to One spot, and No Rail or components connect to it. I got creative and soldered two fuse pools together SLIGHTLY to see if this would rectify my problem, which it didnt.

5. When the amp is flickering between Power-On and Fault, it does make a slight power on Bump to the subwoofers assumeing i have any connected.


:att'n: ~ Finally. A Note. I emailed and called power acoustik, kissed a little butt and got ahold of the Components list and Schematics for the Board! Which as i write this i will look over more closely and examine my board.

Well i think thats it! Please Assist Me in this! Thanks Guys! Please, dont let me down! :)
 
I knew the smaller amp used the 4467/1694. I thought yours had more rail voltage and would use the ones I listed.

You read 0 ohms from what point to the center leg to get 0 ohms? If it was from the B+ terminal to the center leg, that's normal, otherwise, it's not.

You should have checked each individual transistor from legs 1-2, 1-3, 2-3. None should be near 0 ohms.
 
wait a tic,

Ok, well its apparent that i am useing my ohmeter wrong... or something. I am connecting the Positive Lead one of the legs and the Negative/Ground to another... Should i be placeing one of the leads in the Ground or Battery Connectors for the Amp itself? because when i connect one of the leads to say 2-3 i get a Solid Ground.
 
I firstly need to appologize for all the double posting im doing. unfourtunately im under the assumption that this forum does not posses the Edit Button. So that being said, let me go ahead and clearify a few things. I'm kinda learning as i go ;) hehe. Well, I am connecting the Negative lead through the Battery+ and using the Positive Lead to test the Legs of the Trans. and FETS, I am almost positive the FETS are all good. The Trans. on the other hand have me a bit confused... Still connecting the Negative Lead through the Battery+ connector, and when i connect the Positive Lead to all three of the Legs of the Trans' i get readings around 10 Ohms. i am currently working on determining whats going on with the Ohm readings when i connect the Leads to the Trans. itself... When i connect the Positive to Any of the Middle Legs and use the negative lead on any outter leg i get a ground. Not suprised with that, if im not mistaken thats correct right? Now as i am testing here at my desk, i am finding that when i ground leg 2 and measure 1 i get a ground, on All of the Trans. and when i ground Leg 3 and test Legs 1 and 2 i get about half an ohm as a rating... This is all getting so confuseing as i am getting MANY diffrent readings now. So for now i shall stop and wait for an answer. Thank You Perry!

Also if the Schematic would help you to better assist me i can provide it to you.
 
Touch and hold one meter lead to the center leg of a transistor. Then touch the other lead to first the left leg of the same transistor, notice the reading. Then take the lead off of the left leg and move it to the right leg of the same transistor, notice the reading. Check all 8 of the outputs in the manner stated above.
 
Well i did some testing and each of them have at least .5 ohms...

Attached is a picture with the ratings of the transisters...
 

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To Download the files you jsut have to wait like 45 Seconds... Theres a Timer that counts down at the bottom. Then click "Click Here To Download" or if you wish i can upload to a diffrent site. Unfourtunately im on dial-up so Uploading files is Very Slow...

By yank you mean desolder and then check?

Yuck... I dont have a desoldering braid handy so its gonna be a day or so...

Are those ohm ratings bad or do you think it could be a diffrent component possibly?
 
so, heres my question before i dive into this project. So there really Might be Hope for this amplifier? Sorry, but im confused what technique are you refering to when you say add solder to the connections? And the biggest thing about repairing this amp, is that i realllly dont want to have to purchase a bunch of components off of a site like Mouser. Their Shipping Is Ridiculos. Otherwise ive got no complaints. I just want this thing to work =]
 
If you apply additional solder to the solder pads of the transistor and lay your iron down across all three terminals, you can heat the solder on all of the terminals at once and pull the transistor without desoldering braid.

Mouser is one of the best distributors. The shipping on my last few orders from Mouser was less than $4.80 per order.

If you pull the 4 transistors and you find that only one of each part number is defective, reinstall the two that are not defective/shorted, clamp the transistors to the heatsink (VERY important) and power the amp up via a 10 amp fuse. If it works properly, order 2 of each of the defective transistors (so you can replace all 4 in the defective channel).
 
Well thats odd, last time i tried to order a couple FETS from Mouser the Shipping was Horrendous! like 20$ for a part that cost like 88 Cents... Hopefully im mistaken..

im sorry to sound absolutely idiotic, but what do you mean by

If you pull the 4 transistors and you find that only one of each part number is defective, reinstall the two that are not defective/shorted, clamp the transistors to the heatsink (VERY important) and power the amp up via a 10 amp fuse. If it works properly, order 2 of each of the defective transistors (so you can replace all 4 in the defective channel).

So let me take a stab at clearifying what you said..

Ok, so you want me to remove the 4 Transisters that you mentioned in your previous post (two on far right, on both sides of amp) Test them to see what ohm rating they give, reinstall the ones that are O.K. Clamp them to the Heatsink, which i have a question why is that extremely important.. I only ask because i kinda sorta tried to power on the amplifier with them unclamped, just so i could test... 10 Amp fuse, and heres my other question.. You want me to power on the amplifier with the Faulty Transisters Removed? and if it Powers On it means i need to replace the ones that are faulty? Which would mean i need to replace them all on both sides? or are the transisters identical on both sides? Im sorry for all this confusion and such, as i stated before im a newb at this kinda thing...
 
Without being clamped to the heatsink, the transistors can fail within seconds. They can fail before you know that anything is wrong.

There are two parallel transistors per rail per channel. The amplifier can operate with only one transistor per rail per channel. Since it's rare for more than one audio output transistor to fail in each parallel group in an amp like this, it's likely that you will have one transistor of each part number that are in good working order. To determine if there are other problems, you'll reinstall the good transistors to see if the amplifier will power up and produce audio. If the amp powers up and both channels produce clean audio, you'll only need to order the 4 output transistors. If the amp has other problems, you'll continue to troubleshoot until you find the rest of the problems. This can save you from having to place multiple orders for parts.

There may have been a minimum order point when you ordered from Mouser last time. They have no minimum now for items they have in stock.
 
Sounds good, i wasnt aware that the amp could function without them. So that being said im gonna go ahead and try that out tomorrow. Also i went to the Mouser site and i think your right about the minimum order theory because to get the FETS now its only 6$ shipping so woohoo i can fix my other amp and sell it off now. Thank you for all this help Perry.
 
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