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Old 21st October 2012, 10:42 AM   #1
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Question ppi a600 help with repair!

How do I test the sip cards and the dc voltage. the outputs are good it powers up but has no sound red light comes on but just static! another thing is the speaker moves in one way? somebody give me a list of steps i can use to narrow down my problems thanks
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Old 21st October 2012, 05:59 PM   #2
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Well with the speaker moving in one way you have a huge DC output on that channel. Try putting a meter on that speaker terminal and tell us here what DC voltage you read, please...

As for no sound out well with that much DC offset in the channel its pretty much easy to see why you have no music passing thru. So finding the reason why you have such a large DC voltage out is top of the list IMHO.

1: test the DC voltage output of each channel with No RCAs and and No speakers connected.
Make sure your bottom cover is installed while doing any testing on the amp or make a set of clamps out of aluminum stock to hold down all the transistors to the sink surface. This amp uses the bottom cover plate to compress the power devices to the sink surface and without it or some suitable replacement in place the power devices will overheat and self destruct.

2: please post a close up internal picture of the amp. it maybe necessary to post two or more for clarity reason. You say this is a A600 so its not a A600.2 ? The difference being the .2 version uses the SIP cards in each channel.

3: depending on how trained you are at working on car amps you might want to check out Parry Babin's web-site he has links under all of his posts. Just click on them and you will link up to his well designed training page. I suggest it to all if your new to this sort of thing. You will need the info from his web-site to get by inside of any car amp. And as I recall he touch's on the PPI SIP modules in his training course....
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Old 22nd October 2012, 02:02 AM   #3
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I bought the amp fairly cheap, knowing that it was hooked up backwards!, when I opened the amp it had a blown power supply, so I installed z44s and 100 ohm gate resistors, I removed all the bjt"s and did a diode check on all of them they are all in good condition no shorts or leaks. I also reflowed the solder joints on the sip driver cards and the amp itself tested all mpsa style transistors and diodes. I read all of perry babins tutorials ten times over. I tested both channels-L.ch. is 0.8 volts dc. R.ch. is 0.78 volts dc. Should I replace op amps? And should I replace 16 pin SG3525A IC?
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Old 22nd October 2012, 04:52 AM   #4
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both of the DC offsets are within practical ranges to be aligned out with adjustment. in fact both channels might just be out of adjustment. try that before you do anything else IMHO

In these amps there are two sets of adjustments.

1: located near the SIP modules and those adjust bias of the outputs something you might want to check later on before buttoning up the unit. Proper bias is on the order or 100 micro-volts DC across the emitter resistors evenly across each and every one of them or you have leaky outputs and the worst ones will be prone to blow out the first time on full power output of the amp.

100 micro-volts = to 0.0001 Volts DC, you can bias slightly higher but the amp was designed as a low forward bias design like PG and many other US made amps. Bias is something subjective to many but if the outputs are forward biased on even as low as 100 micro-volts then they will not create crossover notch distortion. Which is the whole reason behind forward biasing the outputs in the first place on classic class AB amp designs like this one.

And

2: the other two adjustments are located right behind the power and low ohm LEDs < these are your DC offset adjustments. You should be able to nearly zero out the offset on each channel with these two gain pot adjustments. If not then you look at SIP replacement as the input diff pair on the SIP may be damaged too badly to null out any standard offset the amp may produce. Also note this is a very sensitive circuit and there will be Thermal Drift issues to deal with when setting this adjustment. The measured Dc output on each channel being tested will tend to drift back and forth across the zero line until stable thermal condition's are met. As you try to bring this down to zero the voltages across the diff input pair change and with that so does the temp of each input transistor an so it will see saw back and forth across the 0.000 volts DC line. As you adjust from + something to near zero it will counter drift into the - voltage ranges, and vice versa . It takes patience and some back and forth but you can bring these back to nearly new offsets of less then +or- 5 MVDC output on the speaker terminals

As for replacing the Sg3525 well if the supply is working I say NO. Do you have balanced DC voltage on the rails as measured at the large coil located in the middle of the amp with you black probe connected to the RCA shield??

The RCA shield ground is current limited by the two 10 resistors behind them but as a common ground test point it works just fine to measure for balanced DC rails to the outputs and lower +&- 15 volt rails which are those zener diode regulated pass elements located just after the black plastic diodes and actually the first transistor as you start to see outputs for the amp in fact they are the same transistors but they have zeners and current limits attached to them so they are simple zener driven pass element regulator circuits.
One on each side of the amp and these are the transistors that burn up first if you have been testing the amp without its bottom plate or some substitute in place to hold the power devices down to the sink surface. They die first due to the very high DC voltage drop across them of about 20 volts each. 35 in and 15 out then your dropping 20 volts across those pass elements, 2N6487 or 88 and 2N6490 or 91.

As far as replacing op-amps well, here again I say NO. Although I have had to rebuild a few front ends in the many amps I have worked on. op-amp failure is fairly rare. Have you checked to see if they are getting +&- 15 volts DC to them? And if so then I would scope the signals into the RCAs and then to the large Mylar caps located just behind the gain pot. Those large Mylar caps are the input decoupling caps and a AC signal should be present on either side if the front end is properly functioning. Or you can use a signal tracer to listen to the signals at these points.
These amps had no crossovers built in so all those op-amps were just input buffer, variable gain controlled by the gain pot and then output buffer to the main amp channels, and the big Mylar caps are just to decouple the DC offset voltage so it would not enter the main amp channel...So no way are you getting any DC from your front end into the main discrete amp channels unless those big Mylars are shorting out and that also would be as rare as a blue moon.

Let me know what you find on all of this, and I am glad you read up on Perry's stuff we will be on the same page for the most part as we run through this amp together...I just finished a dozen of them, and I been repairing them since they were new back in the 90's
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Old 25th October 2012, 03:53 AM   #5
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I have a few questions, I only replaced the power supply and gate resistors would that create dc offset issues? and what is the optimal dc voltage on the outputs, can caps internally short no leakage or visible burns? thanks for the help I will be replacing all the outputs for a good repair let me know what you think!
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Old 16th December 2012, 06:12 PM   #6
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I have now repaired three a600's! with blown power supplies and bad outputs ,all matching parts. I would like to know where my probes go to set bias and is it ac or dc voltage? for this location. dc offset is easy to set but i would like to properly learn how and where on my ppi a600's the bias is done thank you for all of youre help
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Old 16th December 2012, 09:10 PM   #7
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Bias voltage is typically factory set at 100 micro-volts DC < or 1/10th of a milli-volt DC > on a typical meter that will read like 0.0001 VDC...Please see Attached PDF file

Caps usually over heat and leak, which can be easily seen by the shrunk up plastic wrappings and the liquid on the PC board. On amps this old I spend the 5 or 6 bucks and just replace them all with Panasonic FC type 105C rated caps. You will find that these are a much higher grade then the original parts used by PPI many years ago, and because they are Panasonic FC they will all be about the same size and fit perfectly. No guessing especially if you lack the proper instruments to test and measure caps. It takes about a half hour to replace them all and clean up and move on to other issues. Shorted caps usually explode, but in some cases they do not, but the heat build up will be apparent on them by the shrunk wrappings on them, and the leakage of electrolyte out the bottom and top pf the cap in question.

Dc offset is adjustable within a given range as PPI added the adjustments to do so with. If your still out of spec after working with the adjustment then you have one main culprit to look at and that is SIP ceramic module channel driver cards. You said you replaced all the outputs and what not so after all that work and if you still can not get proper DC offset on the output them its most likely the SIP modules. The only other thing I would check and make sure all your rail supplies are equal and balanced. Then after that its back to the SIP modules. Perry has a special section in his repair tutorial I suggest you look at before you go any farther on these modules. He has some very good incite to share with you, and he does this very well IMHO. So check out his tutorial and the section about PPI SIP modules before you get too far ahead of anything.

I like my amps to have less then 5 milli-volts DC offset when I am done repairing them. But this just my way of doing things. SoundStream had a less then 15 milli-volt DC offset spec on their rebuilds and just about every manufacturer had their on desired goals for a rebuilt amp to behave like. Most new amps have less then 5 Milli-volts DC offset on the outputs. And most beat up amps have over 30 milli-volts DC offset on their channels that have seen lots of use and clipping.
I am just sharing numbers I know of here after 30 years of being inside these amps. I like my repaired DC offsets low as possible, and like new condition IMHO. After all these were supposed to be complimentary amps so when complimentary amps are in balance and not leaking anywhere the DC offsets should be low, generally speaking...

The DC offset will bounce while you adjust it, and so will the bias voltage setup. On the Bias there is a jumper to be installed located right dead center of the channels outputs. This two pin jumper once jumper-ed will remove all temp compensation from your set point adjustment, thus allowing you to set it more easily. Once set pull the jumper and you should be good to go. DC offset will not be so easy, as it is affected by the thermal rise across the SIP module. You will likely need to allow the amp to thermal SOAK in between adjustments to allow for thermal issues along the way. I set it and then let it idle a while while I do something else, and after at least 10 minutes < I like longer> I come back and re-test to see where the temperature shifts have caused the Offset to change to, and then readjust to my liking. < you might end up doing this several times trying to get solid repeatable numbers to your liking >

Hope this helps some, and Happy Holidays
Attached Files
File Type: pdf Emitter V drop-test.pdf (14.3 KB, 22 views)

Last edited by 1moreamp; 16th December 2012 at 09:37 PM.
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Old 1st December 2013, 04:20 PM   #8
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I have a a600.2 that powers on but has no output any suggestions on where to look
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Old 1st December 2013, 07:22 PM   #9
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It would be better if you started a new thread since this is a different amp.
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