This amp came in with IRFZ44 PS fets and 47ohm gate resistors blown in the PS.
On the output side; Q506/Q507 IRF540 completely shorted and the 100ohm resistor very close to the MIC 4427 crispy but still reading well.
I replaced that 100ohm resistor, all 4x IRF540 with IRF540N, and put a single IRF3205 into each PS bank.
Amp powers and plays out of the sync briefly under 4-ohm load to about 10 amps draw.
Seems like it might be OK but I dont really know these amps well enough to verify full operation just yet.
On the 540 vs 540N, seems parts for 540 and 540A may be scarce which is why I installed 540N for right now. The only 540 I am reluctant to try are the expensive Vishay brand.
Any pointers on what else I might need to check next? If the IRF540N are not suitable are there any suggestions? I read the entire JL 500/1 page but there seems to be a LOT going on with these which I am now trying to get familiar with. I usually pass on servicing JL but alas here one is.
Thank you
On the output side; Q506/Q507 IRF540 completely shorted and the 100ohm resistor very close to the MIC 4427 crispy but still reading well.
I replaced that 100ohm resistor, all 4x IRF540 with IRF540N, and put a single IRF3205 into each PS bank.
Amp powers and plays out of the sync briefly under 4-ohm load to about 10 amps draw.
Seems like it might be OK but I dont really know these amps well enough to verify full operation just yet.
On the 540 vs 540N, seems parts for 540 and 540A may be scarce which is why I installed 540N for right now. The only 540 I am reluctant to try are the expensive Vishay brand.
Any pointers on what else I might need to check next? If the IRF540N are not suitable are there any suggestions? I read the entire JL 500/1 page but there seems to be a LOT going on with these which I am now trying to get familiar with. I usually pass on servicing JL but alas here one is.
Thank you
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No, outputs are not heating up at all with IRF540N, but Im only running the amp for like 20 seconds under light 4-ohm load up to about 10A draw briefly. Board is out of the sync currently.
I do not have any IRF3710Z but if those are generally usable instead of IRF540 then I will order them. Is there a P-Channel complement to those?
Definitely need to order some parts. I'll need all 1206 resistors at least.
I do not have any IRF3710Z but if those are generally usable instead of IRF540 then I will order them. Is there a P-Channel complement to those?
Definitely need to order some parts. I'll need all 1206 resistors at least.
Are the PS FETs heating up?
With 10 amps of continuous draw, I'd expect something to be heating up.
What's the rail voltage?
The 3710Z isn't an issue if the outputs aren't heating up.
I know of no complement to the 3170Z.
With 10 amps of continuous draw, I'd expect something to be heating up.
What's the rail voltage?
The 3710Z isn't an issue if the outputs aren't heating up.
I know of no complement to the 3170Z.
No not noticeably. I’m only pulsing signal briefly out of the sync though. That’s how I do repairs honestly. All looks ok and so next I’d install all ps fets and get the amp back into a sync for heavier testing.
I guess I’ll go through the links on the CD and see if there might be anything else wrong though nothing comes to mind.
Does the MIC 4427 ever tend to fail when output fets fail?
I guess I’ll go through the links on the CD and see if there might be anything else wrong though nothing comes to mind.
Does the MIC 4427 ever tend to fail when output fets fail?
The amp will draw up to about 20 amps for a second or so when the main/rail supply starts. Is that what you're seeing?
Maybe Im not explaining things very well; not sure but Im sorry. Powering up isn't a problem, in fact Im not seeing any more problems with this amp currently. I've tested driving a high signal to a 4-ohm load briefly up to about 10A draw from my bench. Signal on output is pretty clean; thats un-synced. Nothing heats up but Im merely only testing for seconds.
To answer, my Gophert 1620 is not having much trouble powering this amp up even under ~5A current limiting. Sure it's limiting for a second or so, but its powering this amp no problem. IE; normal for this PS. I like this PS btw. Almost never burn up parts with it and its 20A adjustable limit threshold is really nice for a low cost bench power supply. Have you looked this one up?
To answer, my Gophert 1620 is not having much trouble powering this amp up even under ~5A current limiting. Sure it's limiting for a second or so, but its powering this amp no problem. IE; normal for this PS. I like this PS btw. Almost never burn up parts with it and its 20A adjustable limit threshold is really nice for a low cost bench power supply. Have you looked this one up?
For current limiting, I never found a supply that would do it better than a simple resistor in the B+ line.
Even with a 25 amp supply (for amps that could not work with current limiting, most JL amps), I essentially never had a problem with parts failing. The main thing that you have to do is be observant and ready to kill power immediately when you see something that's not right.
I'd try powering up without limiting. If you're concerned about the FETs overheating, clamp them to the heatsink. It probably takes less than 2 minutes to clamp them down.
If you don't like dealing with the clips, this is a good time to use a piece of insulated aluminum stock and binder clips (Tech Tips 9, item 3).
Even with a 25 amp supply (for amps that could not work with current limiting, most JL amps), I essentially never had a problem with parts failing. The main thing that you have to do is be observant and ready to kill power immediately when you see something that's not right.
I'd try powering up without limiting. If you're concerned about the FETs overheating, clamp them to the heatsink. It probably takes less than 2 minutes to clamp them down.
If you don't like dealing with the clips, this is a good time to use a piece of insulated aluminum stock and binder clips (Tech Tips 9, item 3).
Back on this one with all new parts including IRF3205, 47 ohm gate resistors. I changed out the MIC4427 as the original output FETs failed. Using IRF540N still due to supply issues.
Now Im chasing tail.
The amp powered up after installing all new parts, but would not drive clean output past about 5% at 4-ohm whereas before it would. Speaker terminals distorted badly on scope. Seemed to me the new MIC4427 may not have worked so well and so I put the original back in place. Then the amp would not power up at all; very very high current draw. Low ohm LED is lit as well and the amp is drawing excessively.
Im honestly not sure what has happened at this point. Should I remove the output fets and try powering up?
Now Im chasing tail.
The amp powered up after installing all new parts, but would not drive clean output past about 5% at 4-ohm whereas before it would. Speaker terminals distorted badly on scope. Seemed to me the new MIC4427 may not have worked so well and so I put the original back in place. Then the amp would not power up at all; very very high current draw. Low ohm LED is lit as well and the amp is drawing excessively.
Im honestly not sure what has happened at this point. Should I remove the output fets and try powering up?
I removed the output fets and one was measure out of spec. It probably died because of an 540-'N' or maybe because there are more faults in this amp.
I also found a 10R resistor very close to the low side driver blown open. This was not blown a few days ago but definitely now.
I'll try shorting pin1/2 of the 8-pin IC and the Source|Drain of the low side fets.
I'll probably need to order another round; 74VHC132, MIC4427, and IRF3710Z
I also found a 10R resistor very close to the low side driver blown open. This was not blown a few days ago but definitely now.
I'll try shorting pin1/2 of the 8-pin IC and the Source|Drain of the low side fets.
I'll probably need to order another round; 74VHC132, MIC4427, and IRF3710Z
If you get drive signals, you may only need the resistors and the outputs.
It's not bad to have the ICs on hand but you won't have good drive if they're defective.
Remember, by pulsing the remote, you can get 15 seconds of drive after the remote is removed with no risk of damaging the outputs (or the PS FETs) because there will be no rail voltage.
It's not bad to have the ICs on hand but you won't have good drive if they're defective.
Remember, by pulsing the remote, you can get 15 seconds of drive after the remote is removed with no risk of damaging the outputs (or the PS FETs) because there will be no rail voltage.
I've got the output fets removed and the low side jumped S to D as well as pin1&2 of the opamp. Gate drive signal is very bad on the high side fets. Looks like a short, mangled saw tooth not like any of the CD images. There is no drive signal on the low side fet pads at all.
Tomorrow I'll remove the MIC4427 and measure on back, but it would appear poor drive signal is also around Q4, Q5, Q516, Q517. I believe those transistors are OK though.
Tomorrow I'll remove the MIC4427 and measure on back, but it would appear poor drive signal is also around Q4, Q5, Q516, Q517. I believe those transistors are OK though.
Removed the MIC4427.
I dont have a remote/ribbon for the daughter board so I cant really measure the 74VHCs.
74VHC132 vs 74VHC112 14 pin vs 16 pin SOIC. This amp uses BOTH in two different spots. I'm not getting any square waves at all on Q4, Q5, Q516, Q517. Some of these are connected to the MIC4427 inputs.
I guess 74VHC132 have failed. Do the 74VHC112 ever come up failed as well?
I dont have a remote/ribbon for the daughter board so I cant really measure the 74VHCs.
74VHC132 vs 74VHC112 14 pin vs 16 pin SOIC. This amp uses BOTH in two different spots. I'm not getting any square waves at all on Q4, Q5, Q516, Q517. Some of these are connected to the MIC4427 inputs.
I guess 74VHC132 have failed. Do the 74VHC112 ever come up failed as well?
Did you follow the signal out of the 319 into the inputs of the 74hc132s?
Any parts can fail. It's rare but a few times, I've seen the 4427 cause the 132 to fail.
It's time consuming but you can solder wires to the 3, 4, 5 points you need to check and plug the preamp board back in to check signals.
The ribbon cable extensions are a big help with these amps.
Any parts can fail. It's rare but a few times, I've seen the 4427 cause the 132 to fail.
It's time consuming but you can solder wires to the 3, 4, 5 points you need to check and plug the preamp board back in to check signals.
The ribbon cable extensions are a big help with these amps.
