JL 250/1v2 factory defect

[miniman82]

Stby supply gets triggered with remote application same as the main one right?

 

[Perry Babin]

In most of the JL slash class D amps, the low-voltage supply gets switched on and then the main supply powers up a few seconds later. The main supply switches off instantly and the low voltage supply switches off about 15 seconds later when the amp is switched off.

 

[miniman82]

Picking this amp back up.

Just to refresh my memory I powered it up with the rectifier removed, and the main power supply wakes up with no remote lead attached and the standby supply still isn’t making any voltage even with the remote wire on.

So I’m in need of some guidance with the remote circuit I believe.

 

[Perry Babin]

The driver supply should power up then the main supply. The control voltages are supplied through the two large SMD transistors near the LM324 above the power connectors.

Confirm that the 2.2 ohm resistors are within tolerance.

 

[miniman82]

Every pin on the transistors jumps up to 7vdc and so does either side of the 2R2 resistors, assuming that’s not supposed to happen with the remote lead removed?

 

[Perry Babin]

The emitters should be at B+ voltage. Do you have a solid 12+v on the B+ for the amp?

 

[miniman82]

13.8 is what I run as a test voltage, it’s stable and only pulling around 400ma when I looked at those parts.

 

[Perry Babin]

In photos I have, there appears to be a 4.7 ohm resistor just behind the remote terminal on the main board. It may be in series with those transistors. Check it.

There shouldn't be nearly 7v or drop between B+ and those transistors.

 

[miniman82]

Made an error on that resistor, if it is supposed to be 4.7 I currently have a 47 in that spot because the old one had burned. I’ll put the correct value in and retest.

 

[miniman82]

That corrected the low voltage issue, I now have proper B+ getting up to the pre card and those transistors. Main supply still staying on though.

 

[miniman82]

Took some more readings.

Looks to me like opamp #1 on the 324 controls the main supply, and #4 controls the standby circuits.

When I turn on my bench supply (remote not applied), pin 13 which is opamp #4’s inverting input, is getting around 2.5v on it causing it to tell the standby transistor Q203 to turn on. Pin 13 doesn’t budge no matter what the remote terminal is doing.

If I connect the remote wire, pin 2 on the 324 goes from .6v to around 5v and turns on the main supply transistor Q200. Here’s the funny thing though- Q200 stays on when the remote is removed. Even though opamp pin 2 is following what the remote is doing (rising and falling with application and removal of the remote), it stays latched in an on state no matter what I do. Pin 1 on the 324 is staying low as well.

Am I dealing with a shorted #4 opamp here, causing the standby supply to be permanently on?

 

[Perry Babin]

These are the voltages from a 500. I don't know it they're the same as the 250.

LM324 Control IC - U400
0.972
5.73
1.388
13.47
5.80
5.05
12.20
12.29
5.63
9.79
0.000
1.406
5.24
0.969

 

[miniman82]

With remote off I have:

1: 12.9
2: .6
3: .8
4: 13
5: .8
6: .1
7: 11.5
8: 11.5
9: 5.5
10: 9
11: 0
12: .1
13: 2.3
14: .9

 

[Perry Babin]

The voltages I posted are with the amp running.

 

[miniman82]

With remote on I have:

1: .9
2: 5.6
3: .2
4: 13
5: 5.6
6: .2
7: 11.5
8: 11.5
9: 5.5
10: 9
11: 0
12: .4
13: 5.5
14: .9

But I don’t have an ‘amp won’t turn on’ situation, I have an ‘amp won’t stay off’ situation lol.

 

[Perry Babin]

The driver supply has a delay-off of about 15 seconds.

 

[miniman82]

Are you saying the delay circuit is malfunctioning?

 

[Perry Babin]

I'm saying that when the amp powers down, the low-voltage/driver supply continues running for about 15 seconds. Are you waiting for longer than that for the supply to shut down?

 

[miniman82]

It comes on the moment I switch on the bench supply and never turns off. It should not come on at all until remote is triggered, then it should stay on for a bit and shut off.

 

[Perry Babin]

The 324 could be defective but the voltages you posted (pin 12 below 13) are telling pin 14 to go low.