jl audio 500/1 power supply wont turn on

ivkata

Member
2010-12-03 2:37 am
i purchased this amp and another or ebay as broken for parts /repair and for my surprise the other unit worked just fine .This Jl 500/1 dosent look like it was ever repaired in the past ,nor anything looks burn here is my test results :


-when i connect it to my psu the green light comes on ,amp draws 3a current right away ,no power suppy start pulse to be seen .Eventually the power light does away in about 1 min ,current thru the amp is still 3 amp.If i swich the singnal sensing button to on the power light comes back on ,draws a little more current .

There is no dc on the speaker terminals ,no audio output neither .moving switches or pots dosent efect the unit

board: rev 10
 
Post the DC voltage on the 10 pin connector after the power LED goes out. Use the pin numbering shown on the attached photo.


Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
 

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Normal idle current for this amp is 1.5A-1.7A but will draw as much as 3.5A before it settles down to 1.5-1.7A.

If you have the rear heatsink off check output MOSFETS Q504-Q507 IRF540's to see if any of them get warm or hot with no signal and no load. If any do check to see if shorted or leaky. If ok check Q500-Q503 and Q508-Q511. Now if you do have a problem with the output MOSFETS or the output circuit your power supply MOSFETS will get warm or hot but that does not always mean they are shorted or leaky as well.

Do you have a O'scope?
 
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The original Z44s are good enough. I've been using IRF3205s in the most of the JL 500s that I've seen lately (I've done about 10-12 so far) and they appear to be OK. I haven't done enough or checked enough after long-term use to say that the drivers will hold up. Their current rating is high enough but they may run hot.

Are you sure that the FETs failed with absolutely no visible damage to any of the power supply gate resistors?

After removing the FETs and cleaning up the solder pads (to ensure that there are no solder bridges), check every gate resistor to confirm that all are within tolerance.
 

ivkata

Member
2010-12-03 2:37 am
so i removed all the psu fets and few where shorted even tho no visible damage ,after double checking for any solder bridges i tested each and all gate resistors read 47-48 ohms i so believe they are good to stay.two of the outputs are shorted as well q506 ,q507 as well as q509 q510 .I have to replace all the outputs right ,but where do i find them at resonable price
 
so i removed all the psu fets and few where shorted even tho no visible damage ,after double checking for any solder bridges i tested each and all gate resistors read 47-48 ohms i so believe they are good to stay.two of the outputs are shorted as well q506 ,q507 as well as q509 q510 .I have to replace all the outputs right ,but where do i find them at resonable price

avnetexpress.avnet.com/ Sells the IRFZ44NPBF for $.36 each and the IRF540NPBF for $.39 each. :)
 
With the output transistors out of the amp, connect a jumper from leg 2 to leg 3 for Q505 and Q506.

With the black probe on leg 3 and the red probe on leg 1, what is the DC voltage for all 4 output FETs?

If you have defective driver transistors, you'll have to replace them before you can check the drive signal for the output transistor being driven by those drivers.
 

MatthewS

Member
2008-02-22 9:19 pm
I have nothing but trouble using the 'N' series in all the slash D amps i've done as well. I always use a Harris 540, or a Fairchild 540a. Every 'N' I tried to use in any of those amps **** the bed inexplicably and out of nowhere before it even left the bench. The aformentioned were dropped in and away it went happily. Rumor has/had it the 'Z' series works, but I had bad luck with those too. The original parts i've seen are base level 540's, no suffix.

If the N's are working for people, awesome. But I wouldn't feel right if I didn't throw my experiences with them in the ring. They were IR parts BTW, matched and over the course of several of these amplifiers and more than one batch. Who's part is everyone having the best luck with in these?
 
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I have nothing but trouble using the 'N' series in all the slash D amps i've done as well. I always use a Harris 540, or a Fairchild 540a. Every 'N' I tried to use in any of those amps **** the bed inexplicably and out of nowhere before it even left the bench. The aformentioned were dropped in and away it went happily. Rumor has/had it the 'Z' series works, but I had bad luck with those too. The original parts i've seen are base level 540's, no suffix.

If the N's are working for people, awesome. But I wouldn't feel right if I didn't throw my experiences with them in the ring. They were IR parts BTW, matched and over the course of several of these amplifiers and more than one batch. Who's part is everyone having the best luck with in these?

I believe the first JL Audio 500/1 I used the IRF540N in was around 2005 and while I have used the IRF540's as well I found that the IRF540N's were more consistently available from several sources and cost slightly less so I always had them on hand. Perry mentioned IRF540N's don't work in Rockford amps and I vaguely remember repairing a Rockford amp a few years back trying to use the IRF540N's and had trouble with them and switched them out with IRF540's.

With the JL Audio 500/1 amps I always replaced all 4 outputs with the IRF540n's with the same lot number even if 2 of them tested good. I usually use up all MOSFETS with the same lot number before using ones with a new lot number but over time you still get a collection of same number MOSFETS with different lot numbers. With those I use my transistor/MOSFET tester to match the Hfe (gain) and write the gain # on the back of the tab with a fine point Sharpie. I repaired a JL Audio 500/1 for a friend a couple of years ago and replaced the 4 outputs using IRF540N's from 2 different lot #s but gain matched and after 2 years there have been no issues with the amp.

Whether or not a IRF540N works or not depends on how critical the design of the circuit its used in. Better designs are less critical and have a wider tolerance. There are a few differences between the spec sheets of the IRF540 and IRF540N but nothing substantial so in most circuits they should be interchangeable. But as in most things YMMV.