Peavey XC-400, need some help with repairs.

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KiLL3Rw0Lf
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Re: Peavey XC-400, need some help with repairs.

Post by KiLL3Rw0Lf » Tue Aug 01, 2017 6:16 pm

Enzo wrote:Cap can easily have been damaged running backwards. But I just bring up the voltage and find out. A shorted cap might blow fuses, but won't stres the transistors.

No load on the amp output, and look up "light bulb limiter" and make one and use it.
So I had to wait for a few things to come in and also have been quite busy here lately. I ordered a Mega328 transistor tester (and a desolder pump) and retested the output transistors. I'm trying to withdraw from applying voltage as long as I can.

Image

Image

I replaced the original SJ6357 with Peavey's suggested MJ15003. The SJ6357's being discontinued and near impossible to get your hands on. Now to my understanding from the .PDF datasheet here: https://www.onsemi.com/pub/Collateral/MJ15003-D.PDF
The hFE rating for the MJ15003 transistors should be min=25 max=150. I got the following readings using my tester:

#1 hFE=57 Uf=563mV
#2 hFE=62 Uf=563mV
#3 hFE=67 Uf=563mV
#4 hFE=41 Uf=558mV
#5 hFE=57 Uf=558mV
#6 hFE=57 Uf=558mV
#7 hFE=32 Uf=553mV
#8 hFE=74 Uf=559mV

To me this looks like a missmatched set of transistors. Maybe your more professional mind can explain this. To me it looks like #4 and especially #7 is way off balance.

I also tested the main capacitors with my tester. They tested ok. One being right below 5000uF, the other being at or slightly above 5000uF. So those are good and in the correct position.

On top of this I tested the 3 audio transistors. The results are as follows:

JE243G OFF HEATSINK hFE=124 Uf=632mV
JE243G ON HEATSINK hFE=145 Uf=628mV
SJE5332 ON HEATSINK hFE=141 Uf=618mV

JE243G being Peavey's recommended replacement for SJE5331. Another discontinued transistor. I could only find the datasheet for JE243G, which is here: http://pdf1.alldatasheet.net/datasheet- ... E243G.html According to my knowledge, the hFE should be min=40 max=180.

This is starting to confuse me as all of these should be functional in their current state, with minor questions. I have checked to make sure that neither of the two audio transistors are touching their heatsink, causing a short.

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KiLL3Rw0Lf
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Re: Peavey XC-400, need some help with repairs.

Post by KiLL3Rw0Lf » Tue Aug 01, 2017 7:24 pm

Oh, man. I feel like a complete idiot right now. Shame shame shame shame shame. XD

After searching a bit more I noticed you had posted a few replies on another board on here.
Here is the link:https://www.peavey.com/forum/viewtopic. ... 1&start=15
This post right here struck me. Oh, man. I'm stupid:
The old 400 series had a row of transistors bolted to the rear panel. each had two screws, and a plastic insulating cover on each to protect you from shock. The transistors plug into sockets. Remove the screws, and you can pull the part out of the socket. Note one screw holds the cover, the other screw makes the electrical connection. Make sure to align the socket holes into the panel holes so the screws do nit touch the panel. Also there will be a thin mica washer under each transistor to insulate it from the panel. very important not to lose or damage those.
I thought that was a thermal pad so I replaced it with a non-conductive thermal paste since a few of them received damage when I and the previous person deconstructed the board and thermal paste provides a better heat transfer to the heatsink then what pads do........ Uhg, my stupidity.
I have them right here, and after a quick Google search, realized what it was.

Image

I will have to order replacements. This is probably a main issue. This and there were a few blown power transistors in the originals. I'll probably coat a portion of the retainer bolts with a non-conductive substance to keep them from shorting too. Wow, this whole time I have been grounding out the amp....... Thank you for your help.

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Enzo
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Re: Peavey XC-400, need some help with repairs.

Post by Enzo » Tue Aug 01, 2017 7:40 pm

OK, in no particular order.

It is MJE243, not JE243. Motorola/ONSemi will be the source usually. Mouser should have them. Also, if Peavey parts department no longer has stock of 5331, they will have the equivalent to sell you. I buy most of my parts generically, as from Mouser, but I always stocked the 5331/5332 types from Peavey, partly because the wire leads will be already bent to exactly fit the holes on the board, including the mounting hole. hey, I am lazy.

SJ6357 was a house number decades ago. That number series was changed, so they are now called 70484140, or 84140 for short. MJ15003 is what it is under the skin. You can freely substitute the MJ15003 for the old SJ6357.

Don't worry about the hfe. Your meter tests transistors at a very low voltage, just enough to turn them on, and at tiny currents. You MJ15003 has specs at higher currents. In fact the 84140 number means:
8 - NPN
4 - amperes current at which hfe is specified
140 - voltage rating at load.

The fact the hfe varies a little at 1 volt matters not at 4Amps. They will all be close enough in the amp circuit, also the emitter resistors, those under 1 ohm ones - are there to assist the transistors to share current equally.

Similar warnings about the cap meter. It is useful to measure capacitance, but a meter again works at 1 volt or two, so cannot test what the cap would do at 50 volts. But in fairness, if the cap is shorted, it wouldn't measure 5000uf.

Here is a rule of thumb in my shop. If the MJ15003 output transistors are bad, I always replace the 5331/5332 drivers as part of the deal. Even if they test OK, they were stressed by the larger failed transistors.

Aha, just read your latest post, yes, you need to insulate those transistors or they ground out the power supplies. So read my above discussion, but do corect the missing mica washers.

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KiLL3Rw0Lf
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Re: Peavey XC-400, need some help with repairs.

Post by KiLL3Rw0Lf » Tue Aug 01, 2017 8:38 pm

Enzo wrote:OK, in no particular order.

It is MJE243, not JE243. Motorola/ONSemi will be the source usually. Mouser should have them. Also, if Peavey parts department no longer has stock of 5331, they will have the equivalent to sell you. I buy most of my parts generically, as from Mouser, but I always stocked the 5331/5332 types from Peavey, partly because the wire leads will be already bent to exactly fit the holes on the board, including the mounting hole. hey, I am lazy.

SJ6357 was a house number decades ago. That number series was changed, so they are now called 70484140, or 84140 for short. MJ15003 is what it is under the skin. You can freely substitute the MJ15003 for the old SJ6357.

Don't worry about the hfe. Your meter tests transistors at a very low voltage, just enough to turn them on, and at tiny currents. You MJ15003 has specs at higher currents. In fact the 84140 number means:
8 - NPN
4 - amperes current at which hfe is specified
140 - voltage rating at load.

The fact the hfe varies a little at 1 volt matters not at 4Amps. They will all be close enough in the amp circuit, also the emitter resistors, those under 1 ohm ones - are there to assist the transistors to share current equally.

Similar warnings about the cap meter. It is useful to measure capacitance, but a meter again works at 1 volt or two, so cannot test what the cap would do at 50 volts. But in fairness, if the cap is shorted, it wouldn't measure 5000uf.

Here is a rule of thumb in my shop. If the MJ15003 output transistors are bad, I always replace the 5331/5332 drivers as part of the deal. Even if they test OK, they were stressed by the larger failed transistors.

Aha, just read your latest post, yes, you need to insulate those transistors or they ground out the power supplies. So read my above discussion, but do corect the missing mica washers.
Actually, looking at them the original insulators are OK. to hold the bolts on the power transistors in place could I use high temp hot glue? That would insulate them good enough as hot glue is non-conductive and would keep them from hitting the sides of the heatsink. Another not, that was my mistype. It is the right audio transistors. They were unbent. I just bent them myself. It didn't take much at all.

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Enzo
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Re: Peavey XC-400, need some help with repairs.

Post by Enzo » Wed Aug 02, 2017 12:00 am

It isn't hard to bend the wire leads, of course, but for me, the parts don't cost any more than generics, and they are already to drop in. Just my personal preference.

No you cannot use hot glue. Are not the transistors plugged into sockets? The sockets should have little ridges around the screw holes that keep the screws centered, so they never touch the sides of the holes.

By the way, does your rear panel say 400B? I think earlier you posted a 400BH board, which is different. I want to be sure I am on the same page as you.

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KiLL3Rw0Lf
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Re: Peavey XC-400, need some help with repairs.

Post by KiLL3Rw0Lf » Wed Aug 02, 2017 6:41 am

Enzo wrote:It isn't hard to bend the wire leads, of course, but for me, the parts don't cost any more than generics, and they are already to drop in. Just my personal preference.

No you cannot use hot glue. Are not the transistors plugged into sockets? The sockets should have little ridges around the screw holes that keep the screws centered, so they never touch the sides of the holes.

By the way, does your rear panel say 400B? I think earlier you posted a 400BH board, which is different. I want to be sure I am on the same page as you.
It is indeed 400BH.

About the hot glue, this is what I was talking about as I feel I made myself unclear.

Image

I know it's a bit blurry. My phone does not focus really good up close. None the less it allows you to see what I am talking about. I noticed that if I slide the all the way to one side it can almost touch on some of the sockets while on others it can touch the socket. So i applied a small dab of hot glue to keep it off of that side. This does not affect the transistor or mica washer being placed onto the board. It actually helps to hold the bolt in place as I put the transistor on. If this is still not good I can easily undo it. I'd be very surprised if the board ever got hot enough to remelt this. My gun has to get rather hot before it starts melting the glue. I've burnt myself with it before, so I know :lol: .

Anyways, I've been putting a few on using this method and poked around with my multimeter. I have no closed circuits so far. Everything is looking good. (I will say no closed circuits because I know some get all upset when you say no resistance. lol)

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Re: Peavey XC-400, need some help with repairs.

Post by Enzo » Wed Aug 02, 2017 10:25 am

It won't hurt it, but likely won't help either. See the screw is centered already, the holes are designed that way. I have never seen one where the screws grounded out.

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Re: Peavey XC-400, need some help with repairs.

Post by KiLL3Rw0Lf » Fri Aug 18, 2017 8:19 am

Enzo wrote:It won't hurt it, but likely won't help either. See the screw is centered already, the holes are designed that way. I have never seen one where the screws grounded out.
I went to do some testing then realized I didn't have any more 8A fuses. So ordered some more and that was a mess with receiving wrong ones and reordering and stuff. Anyways, I put a fuse in, quick blow this time, and tested the amp. I hooked up a sub I got from a old surround sound system, since I didn't care too much for it. First, without any input plugged in. There was no humming, buzzing, or static. Second test I got one of my guitars and plugged it in. For the wattage of the sub I could turn the amp up about half way. I believe the sub to be 80w (It's 4ohm, tested with my multimeter). I turned it on with the volume turned to 0 and slowly increased it. There was still no sound no matter the volume level. The fuse didn't blow so I guess that could be a good thing. I also noticed that the compressor wouldn't kick on. I flicked the switch and nothing happened. No light turned on. Then again the LED could have blown. I'll test it. I'm working on checking all connections and rechecking solder joints. There doesn't appear to be anything blown, by physical appearance. I may poke a few things and check. I've also checked the 2 internal fuses near the power caps. The power comes on so I know it is receiving power.

Perhaps I'm looking in the wrong place now and the issue is in the front controller board? This is rather confusing to my noobish mind. XD One day I shall get this! Right now I am having plenty of fun entertaining myself with the confusion.

Edit: The LED input display or whatever it is. My mind pulled a brain fart. That LED display up front which shows how strong the input is. I also noticed that didn't light up. Once my brain reboots It will probably hit me. I'm going to trace the input and see if there is an issue there. Also trace the volume controller in the front board.

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