JL 500/1

[2many]

I have a 500/1 with burnt Q602, Q606, Q607 and R600 thru R607 along with Q600, 601,603,604,605 testing faulty.

I have read the basic repair info page and have experience repairing electronics like home appliances, game consoles and pagers...yes, pagers but has been awhile since doing so. I have since moved on to computer related things.

now when I got this amp, the green led would turn on but that was about it. Since I didn't have time to mess with it at the time, it got shelved. Long story short, I am tired of using a mid range amp for my subs and would like to attempt to repair this one.

I do have a multimeter and solder irons, but no power supply, spare battery and/charger and very little money at this time. I do have an oscilloscope but I have no idea if it works any more since it's buried outside in the shed and the probes are m.i.a.

now, all i want to do is gain some advice on what else I should check before spending money on components. I also should point out this is my first attempt at fixing an amp.

[Perry Babin]

Q600-607 and R600-607 typically need to be replaced. Sometimes the drivers fail as well. You can check those after removing the FETs.

You also need to check the output transistors.

Dig the scope out and see if it works. You can use a piece of wire for a probe.

There are plenty of threads covering repairs of these amps if you want to search through the forum.

[2many]

I'll dig the scope out tomorrow and I will continue to search through the forum.

sometimes it just takes a point in the right direction to find what I'm looking for

[2many]

dug out my ancient scope and it works, RCA wo-505A and found a couple of ac/dc power supplies, ETP model 6000 plus I converted a computer psu to a dc power supply.

so I took out the power fets, resistors and did some testing with my multi on the outputs but I am waiting on my desolder braid to show up so the outputs are still in the board. I did write down some values and two of the outputs appear to be faulty but with them still in the board I cannot be so sure, so I will consider them untested at this time.

reading up on testing Q608-Q611 and how to use this scope. been 15 years since I last used one and even then it wasn't this old.

I would be further along with this but I had some pc projects that needed to be finished first

[Perry Babin]

Do you see a clean square wave on the 3rd leg of the driver transistors?

[2many]

well, no square wave on any of the driver transistors and no volts on Q608 & Q611. when I probe with the scope the solid reference line just widens vertically/blurry.

so I probed with my meter and seen 12.16V same as my source on Q609 & Q610.
all this with ground probe on amp source ground

[Perry Babin]

Q609 and Q610 should have 12v on their tab (center leg). All 4 transistors should have approximately 5v on their 3rd leg. If the voltage on the third leg is near 12v, the PNP drivers (Q608/611) have failed.

[2many]

ok I guess my shopping list should include the Q608/611 (WY720). so my question then is this, at this time should I start looking for the parts that I know are bad or should I also replace Q609/610 (UY725).

oh and Q609/610 have 12v on center tab and 3rd leg

should've mentioned before I have the rev 11 board for reference reasons.

[Perry Babin]

Are Q609/10 shorted between legs 2 and 3?

[2many]

with them still in the circuit, they do not test bad.