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Old 20th April 2012, 03:19 PM   #11
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They will not read the same while in the circuit.

When you state that the transistors read ..ohms, you need to state where the black probe was placed and where the red probe was placed.
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Old 20th April 2012, 03:30 PM   #12
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sorry, i was refering from the source to the drain, probes either directioni get 17 ohms, then with either lead from source to gate or drain to gate it steadily rises k ohms.
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Old 20th April 2012, 05:12 PM   #13
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all of the TIP35c's look like this
Click the image to open in full size.

and the TIP36's like this

Click the image to open in full size.
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Old 20th April 2012, 06:16 PM   #14
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Thank You ! Perry for chiming in. Your help and guidance is always appreciated my friend.


Spicy Mchaggis:

If this is your first time inside a car amp then most of what I have been directing you to do is has been missed or has just flown by misunderstood. For this I must apologize to you. Perry has a wonderful site and it has everything clearly defined and well described to even a laymen at this type of work. He is also a much better teacher then I, as I tend to some what forget that lots of folks are not as experienced as myself. My apologizes to you if any of this has happened to our work here in this thread.

I admire your tenacity to learn and your attempt to preform your own repairs.
I want your gear to get repaired properly, just like Perry does. Your repair can not be completed unless you are able to follow his or my lead while using the info garnered from Perry's web-site on the simple how-to's of which his web-site teaches so clearly.

We still have not located the reason why the power supply failed like it did, and this worries me a bit because if we don't find the reason for all the symptoms your repairing, this amp will go up in smoke the first time you power it up. We are going to have a bit of a tough time trying to get you thru the next few phases if Perry's web-site is not clearly understood on your part. You will need to know how to measure simple transistor ohm meter readings in circuit to get thru the rest of the repair work. So please tell us what it is that Perry's site does not explain fully for you, so we might add in some more details for you in efforts of helping it all to be clear to you.

A suggestion: When measuring transistors and fets in circuit if your reading don't prove clearly what you want to know, then may I suggest that you lift the center leg of any transistor of fet out of the circuit board solder joint and then read across the leads in pairs again with the lifted lead always in the readings, and with the black and red probes reversed for a second set of readings across each device in question. The lifted lead takes part of the device out of circuit so you can get clearer readings from that lead to the other two leads somewhat independent of the surrounding circuitry.
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Old 21st April 2012, 12:04 AM   #15
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I was just unsure if the transistor readings could be done on the board and what readings I should actually be getting? I have no problem desoldering, so just pulling them to check is no big deal. I'm sorry that I don't know as much as I should for doing this type of repair, but I have always been a do it yourselfer.
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Old 21st April 2012, 04:12 AM   #16
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ok, so if I get readings like this for a TIP36c then it is good

Click the image to open in full size.

and reverse for TIP35c where 1 and 2 have .5x

what is a good next step if these are all good and the irfz44's and the gate resistors are getting replaced anyways? along with the gate drivers. How can I find a good possible reason all of this could have happened?
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Old 21st April 2012, 04:27 AM   #17
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Quote:
Originally Posted by spicy mchaggis View Post
I was just unsure if the transistor readings could be done on the board and what readings I should actually be getting? I have no problem desoldering, so just pulling them to check is no big deal. I'm sorry that I don't know as much as I should for doing this type of repair, but I have always been a do it yourselfer.

This is all fine and good, but in order to test the possible reasons for the failure the test methods that Perry's web-site teach are pretty much mandatory if success is your desired goal. I am at fault for placing your experience higher then it really was based on your use of terminology in your thread posts.

You do not have to remove the transistors completely to find out if they are shorted. The simple lifting of the center legs of each device will allow you to get definitive readings on most ordinary DMM's. With time and experience you won't even have to do that.
On any amp with multiple outputs like this one, a single bad output device will blur readings across the entire set. They will all look like they are defective when compared to the other channel just across the board. This is due the fact they are paralleled to gain current sharing and power handling factors.

There maybe nothing wrong with the outputs if so channel A will read like channel B. I have seen these amps blow there power supply because the amp was running too low of a speaker load. These are not 1 ohm amps but I have seen this failure because of just that reason. And once the power supply was repaired the amp went right back into service, until it failed again the exact same way due to being run into incorrect speaker impedance's.

Please post your questions about any readings you don't understand like you did for the gate resistors. they were burnt open or up in value and needed to be replaced just like the Mosfets. The gate drivers are likely damaged also so please replace them as a matter principal as they usual do not take this type of failure too well IHMO.

Once you have tested the other possible failure points like the outputs and drivers, then you will need to test the rectifier diodes between the mosfets and the TIP outputs. These are simple diode junctions so reading them is less complicated then transistors.
If all this checks out then we might be a point of reassembly and clamped back into its sink for a simple power on test. but this test should be preformed with some sort of current limit on the 12 volt supply feeding the amp, so you get a chance to see if you missed anything before the amp damages itself again just from testing. A 12 volt head light inline in circuit on the 12 volts supply will work as a current limit.
But all of this is further down the road while your checking all the other possibilities before we get to simple power on testing.

This can be complicated I know. Just because Perry and I can do in our sleep is only because we have done it so many times before its just second nature now to us veterans. Once you have seen it all, it's all the same pretty much. I enjoy it when its something new and unusual, then I learn something new also...
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Old 21st April 2012, 04:33 AM   #18
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Quote:
Originally Posted by spicy mchaggis View Post
ok, so if I get readings like this for a TIP36c then it is good

Click the image to open in full size.

and reverse for TIP35c where 1 and 2 have .5x

what is a good next step if these are all good and the irfz44's and the gate resistors are getting replaced anyways? along with the gate drivers. How can I find a good possible reason all of this could have happened?

Looks like they might just be fine. Transistors short junctions when they fail or blow completely open. So be looking for very low ohms across all the leads if they are shorted in anyway. Shorted devices are the most common.
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Old 25th April 2012, 03:39 PM   #19
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Alright, all of the transistors checked out, everything is cleaned and reassembled. I just want to know the best simple start up procedure for this amp. I understand to put a small fuse in line, is a 15 to big? and you also metioned about putting in a headlight for a current limt. will any headlight work or does it have to be under a certain wattage?
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Old 25th April 2012, 05:32 PM   #20
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Ok, tested, turned on, and plays perfectly. Thank you so much for your help, Thank you perry for the website and all of your hard work that you put into it. 1moreamp, thank you for bearing with me through my learning curve I couldn't have done this without you!!!!!!!!
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