Xtant 1001DX Output transistors needed - Page 2 - diyAudio
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Old 7th October 2004, 04:02 AM   #11
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I'll try to explain this as best as possible. Luckily, I have no real technical background (aside from the past couple of years of working with Sergey), so all of my knowledge and explanations should be pretty practical. I won't go off on a tangent about how things work, just how to measure and replace them.

Before we start, you're going to need a few pretty simple and obvious tools, like a multimeter (set to ohms auto) with some probes (I prefer sharper probes, it's easier to poke around), a half-decent soldering iron, and HEAT SINK COMPOUND. The heat sink compound is a MUST for this amp - the way the xtant is designed makes it really awesome at keeping cool (provided that you're not running it into too low an impedence), but it won't work without enough heat sink compound there. Don't overdo it, just a moderate dab on the back of any new parts. Having a power supply (even a small one, about 3 amps for this unit) is a great help with fixing things. Powering them on with no load is a great way to identify where your problems are occuring, especially after you've replaced all obviously shorted parts. Oscilloscopes are great, but can't always be expected. If you DO happen to have one, let me know, and we can go on troubleshooting from there afterwards. I can get you some pictures of both the bad and good waveforms.

I'm going to throw in a couple other basic things as I post this. Getting your bearings in an amp is the most important thing to learn before diving in. Luckily, the basic things are so simple anyone can learn them. The power supply, which will usually be the problem with amps that don't power on at all, is always located next to the transformer. On this amp, it's on the far right - in case you've never worked with anything before, that'll be the donut looking thing wrapped in thin, multicolor wires. The power supply transistors (which will almost always be MOSFETs) are easy to identify - they're any banks that the wires from the transformer are directly connected to. The output, the other important section to identify, is identified in mostly the same way - it's located next to the inductor, which is very similar to a transformer, except there's usually one one color wire, there's much less of it, and the wire is much thicker. The output is, generally speaking, where you should look first for problems in an amp that does power on, but still isn't working. Transformers and inductors won't always look like this, but the vast majority of the time this holds true. It's not a good rule for identification, but I find that there's frequently less transistors (which are MOSFETs about 50% of the time in class AB, and always in class D) in the output than in the power supply.

I was going to post something about reading transistors (picking out part numbers, manufacturer codes, & date codes), but that's really not important here. It's a good rule to make sure that all of the parts in a bank are from the same lot, but since you'll be ordering your parts at once, they will be. Just replace them a bank at a time, and you'll be golden.

Okay, let's start measuring! I've thrown in some pictures to help, you'll only be using your multimeter through all of this (Which is, surprisingly, definitely your most valuble tool in fixing amps. While you can do this with an oscilloscope, and we have one on every lab table here, we always start with the multimeter. Why pull out the big guns when a .22 will do the trick?). In this first picture, you'll see the power supply, which is on the far right of the amp. On the right is a 540N - don't even bother with it, they just about never blow. It's easy to accidentally cut it out while you're taking out the other bad parts, so just keep it in mind. On the left is the first bank of transistors, they should all be IRFZ44 (which are MOSFETs). If any of them are cracked, charred, or split open, take them all out. If you're not used to taking transistors out of boards, or are new to soldering, it's easiest to cut the parts off at the pins and remove each pin individually by gripping it with tweezers (small pliers work well, too) and heating it at the base. This is a double-sided board, so you can do that right from the top. Cake. If there aren't any split or blown, you'll have to measure them. Since these are in the power supply, you're going to measure between pins 1 and 3 first. Check them all, if you see any shorts (less than 100ohms. Be sure you pay attention to the meter - some of them will read in kilo- or megaohms, which can be confusing at times when you're not paying attention), there's a bad part in the circuit. Normally you'd hunt down the bad part, but in this case, just remove them all. If there are no shorts between pins 1 and 3, check for the less obvious shorts by measuring each part between 1 and 2, and 2 and 3. If you see no shorts, they're all just fine, and you can move on.

Click the image to open in full size.

Now, for the next picture. In this one, you see the bank of rectifiers on the left, and another bank of transistors on the right. Ignore the rectifiers - these are so unlikely to be blown that they're not even worth measuring in your initial testing. The bank of transistors here, which will also be IRFZ44, should be measured with exactly the same process as you used before. Now, that's all easy, but here's a really important note: if you didn't replace the previous bank, but you had to replace this bank with IRFZ44N, you MUST go back and replace the other bank as well. If you don't, there'll be a flux imbalance in the transformer, which isn't a happy thing. Now, if you're really ambitious and think you'll have a use for these parts in the future, set them aside and post about it. If you don't already know how, Sergey can show you how to test them with your multimeter to see if they're good. This is actually not a bad practice, there's very little risk in using "harvested" parts as long as you check them thoroughly, and it can really be a big money saver.

Click the image to open in full size.

Alright, now that we've got the power supply out of the way (surprisingly easy, wasn't it?), we're ready to check the output. The parts here are IRFZ44N, which are also MOSFETs, and are the part that you probably replaced the IRFZ44 with. They're a fairly common part, and if you fix other amps, you'll probably see them popping up pretty often, as I'd put my money on them being the most common part in car amplifiers. The next picture shows just that - it's an h-brdge power supply, so it's split into four banks of two. Since this is your output stage, you'll be measuring between pins 2 and 3. It's pretty much the same process as before, just a different order - check between pins 2 and 3 first. Each bank of two is a different circuit, you should probably test them all as banks. If there's a short in either, replace them both. If there's no short between 2 and 3, check 1 and 2, and 1 and 3. If there's no shorts, it's probably just fine. Once you're done with all four banks, you're just about through the woods!

Click the image to open in full size.

The next three pictures are the last task - checking the resistors. Check all of the ones in the pictures, which will be directly on the other side of the transistors. They're 10 ohms, as I said before, so any measurement between 9 and 11 ohms is fine. If it's charred (there's a good picture of a toasty one there), don't bother measuring, just pop it off. You can replace these individually, there's nothing to worry about. Once you've done all the resistors, that's about it. There's one more step, but it's pretty much unique to this amp, and that's the U2 and U3. It's labelled as PAIN IN THE BUTT on the picture, because that's what it is. It's an obsolete part, and very hard to cross reference. If this is blown, it'll probably be obvious (as in this picture). I honestly don't know which part to replace this with, but Sergey can let you know if yours is blown.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Well, that's about as far as I can take you now! If you have a power supply, try turning the amp on without a load (very important). Minigrabbers are the easiest, just find a way to clip them to the power and ground terminals respectively (don't hook up the remote at first). Turn on your power supply, and the amp should draw no current. If everything's quiet on that front, short the power and remote terminals together (anything works - alligator clips, pliers, etc). The amp should power on, and just the red light should come on. It should only draw about 2 to 3 amps, and it should stay at 12v. If it passes that test, and you're comfortable with the work you've done, try hooking it up and giving it a test run!

If you hit any bumps, or get through this and it still doesn't work, let me know. If you need parts, we can get them to you pretty fast - if we send them USPS priority, it'll be about $3.50 no matter how many there are. We'll sell you however many IRFZ44N you need for $1.00 each, and throw in the resistors for free, just let us know how many you need. If your U2/U3 is blown, we can probably help you get that part for a good price, too (we have to order a couple ourselves). Just let us know!

As I probably said before, feel free to post any questions you have here, or e-mail us. Hope this helped at least a little!

- Sara
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Old 7th October 2004, 04:06 AM   #12
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I forgot to make a comment, that applies only to this amp, really. These amps have a LOT of problems. Sergey, was has a BS in Electrical Engineering and more than 6 years of experience in repairing amps, has to work on these for quite a while. The odds are pretty good that it won't work after this. If you have an oscilloscope, he can tell you how to test it further... if not, you'll probably have to get it repaired professionally.
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Old 7th October 2004, 05:06 PM   #13
Stooo is offline Stooo  United States
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Wow thank you for all the replies I have been so busy lately and have not had a chance to look boack for quite awhile. I only have glanced at the posts but I will read them thoroughly when I get off of work. I found the irfz44 and bought 25 of the and 20 of the irfz44n and they will be in tommorrow. I have found on ebay a kit of 1206 smt resistors. I have my fluke dmm too so I am just about ready to start as soon as I read more. Thank you again
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Old 9th October 2004, 04:22 AM   #14
Stooo is offline Stooo  United States
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Hi I am getting ready to take out the Irfz44 now and I looked at the backside and my u2 and u3 are not looking too good so I figured I might as well replace those while I am at it so If you have a few to sell let me know. Thank you again for your detail and time. I have a few other I am attempting to repair ( one at a time of course). They are the 1001dx , 603x, and (my favorite) 3300C all of them the older style which I like more than the newer ones. So hopefully I
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Old 16th October 2004, 06:58 PM   #15
Stooo is offline Stooo  United States
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Ok I have the IRFZ's replaced as well as the 10 ohm smt resistors. I do not know if the u2 and u3 are shot but time will tell. I powered it up using my powersupply (radio shack) and the middle light came on for low voltage. dont know if it is because of my power supply or something in the amp so more testing to come with a different power supply.
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Old 17th October 2004, 02:26 PM   #16
Stooo is offline Stooo  United States
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Update After replaceing the IRFZ44 and 10 ohm smt's resistors I decided to replace the irfz44n the amp would power on with the low voltage led lit up and then it would goto the red (power on) led. So feeling brave I thought to hook my CD player's output from my home system to it and an 8ohm speaker i have laying around. I had the gain at -10 and the dial way down. Then I could hear what sounded like a really small relay being triggered over and over again, it almost sounded like static but still no output. I listened closely and could not hear where it was coming from, as i turned the gain up it sounded like it was going from the power side to the output side. Now the low impedence light comes on when powered up but it switches between the led and the low voltage led. ????
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Old 19th October 2004, 11:39 PM   #17
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I sounds like a problem with the gate driver. Unfortunately, you can't really check that without an oscilloscope.
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Old 20th October 2004, 02:33 AM   #18
2pist is offline 2pist  United States
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Unless you have a dvm that measures frequency.
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