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Thread: Peavey XR400 (200H Power Module)

  1. #1
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    Peavey XR400 (200H Power Module)

    Hi, I recently acquired a Peavey XR400 Amp (non working). No power light-completely dead. Upon having a look at the power module- it was apparent that some previous "repairs" may have added to the problems. The 5 watt cement resistors at R22, R23 had been replaced by smaller 1 or 2amp resistors "pig tailed" together -they were completely fried.
    The power resistors comprised of a mixture of 3x SJ6932 and 1x 2n3055. One of the SJ6932's was shot. Also several defectve 1N4148 diodes. Clearly I need to check the whole board and replace the dodgy components.
    I am not 100% sure about a couple of components on the board and getting replacements and was hoping that someone could suggest some specific replacement part numbers (not Peavey part numbers) from Mouser/Digikey- I would then be able to obtain suitable replacements in the UK.
    I have uploaded some pics(hopefully) of the parts in question.
    1. 0.1uf/100volt capacitors C4,C10,C11,C12,C23,C24.
    2. Glass capacitors at C1, C2.
    Additionally are there any suitable alternative replacements for the following transistors:-
    Q1 and Q2 -2N3904. Q4 -2N3642 and Q5 -2N3638.
    Any help would be appreciated.



    John H.

  2. #2
    Senior Member Enzo's Avatar
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    DO you have any reason to think those caps are ACTUALLY bad? In my experience, those almost NEVER fail. (having said that, it now becomes almost a certainty they will...)

    2N3055 is in fact one of the Peavey listed replacements for the SJ6392. The more modern replacement would be the MJ15015.

    REplace the 5w resistors with the proper 5w types - 0.33 ohm.

    Be aware that some of the 1N4148 diodes have parallel resitors that might confuse your tests.

    2N3904 is one of the most common small transistors there is. I don't know why you'd need to sub it. An MPS8098 would be a nice pair to use if you must.

    Q4,Q5 - look at the schematic. They are listed as 6530 and 6533 respectively. (MPS6530, MPS6533) These are limiter transistors in the circuit, most anything would work. MPS6531 and 6534 could also be used.
    Education is what you're left with after you have forgotten what you have learned.

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    Peavey XR400 (200H Power Module)

    Hi Enzo, I was hoping that you were going to respond and help me out.
    I have to confess that my rush to get the amp powered up and with the clear discovery of visually obvious faults (the botched replacement 0.33R/5W resistors) and charred adjacent resistor R21 -47R and damaged 1N4148 diodes (no exterior casings/markings) at CR3 and CR7 resulted in me replacing only the obvious defective parts and not checking further (lesson learnt!)
    Upon power up R21 glowed red and R18 began to smoulder.
    Subsequent checking revealed that Q7 -SJ6392 was duff. (Q11 was 2N3055).
    I will take your advice and install 4x MJ15015.
    That is about as far as I have got so far -I intend to give the board a thorough check at the weekend (which I should have done in the first place) and see which parts are defective.
    My query with regard to the capacitors was purely to establish what would be appropriate replacements (if required) currently I have no suspicions about them being defective- it was just to find out suitable replacements.
    I have managed to obtain some 2N3904's however the MPS6350's and MPS6533's are not that easy to obtain in the UK -hence the query re suitable alternatives.
    I'll submit a further post upon checking the whole board this weekend.
    I have attached some pics of the board -note I removed R21 after I fried it.
    (Advice re replacement caps would be appreciated)
    John H.



  4. #4
    Senior Member Enzo's Avatar
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    If you don't have MJ15015, then MJ15003 would work or even good old MJ15024. A nice fresh set of outputs is good. And make sure all those cement 0.33 ohm 5w resistors are intact.

    Whenever outputs burn out, it is good to replace the drivers too. Look at the schematic, R18 and 21 are burning. Excess current does that. Where must that current be coming from? In each case, through a driver transistor, they are probably shorted. Those are the TO126 5331 and 5332. %331 is a Peavey house number, and you could get them from EuroPeavey I'd wager. But they can be replaced by MJE243 and MJE253. make sure the leads are in the same order though. And if yo0u have a TO126 that is more available to you, as long as it meets the specs of the MJE243/253, it should work.

    So check them, and R16,17,18,21.

    You already checked the 1N4148s, but make sure CR3,5,6,7 are OK. Note CR5 and CR6 are really just one component - a dual diode. Test it like a diode, but the voltage drop forward will be twice a normal diode. It is a Peavey part, I am not aware of a generic for it. it is mounted in a hole in the heatsink.

    At the output, R25, make sure it is not open.

    CAps are caps, value and voltage. Really, don;t worry about the little film and ceramic caps unless you find a bad one. Very rare. And any type will work.

    The little 6530 limiters are not critical, use just about any little transistor with similar specs. Are they shorted? The MPS6531 is a 40v up to 1A transistor.
    Education is what you're left with after you have forgotten what you have learned.

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    Peavey XR400 (200H Power Module)

    Hi Enzo,
    Thanks for replying.
    I followed your intial suggestion and ordered some MJ15015's. Ordered from Hong Kong- not received yet- they are Motorola and I do not expect pirate parts!
    I checked an old parts box and surprisingly found a couple of MZ 2361 -double diodes -the original on the board was sheared in two -but hidden within the heat sink hole- and not visible.
    I also obtained (from the US) as a replacement for the MPS6533 transistor -the suggested PV replacements ie 2N3638. I am having a bit of trouble working out the pinouts for this device. It is a Fairchild make within a TO-105 package, Ive attached a photo showing the legs. Could you assist and update me as to which legs are c/e/b please.
    Many thanks,
    John H.

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    Senior Member Enzo's Avatar
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    Generally I expect those to be EBC across your 123. Same as a TO39 basically.
    Education is what you're left with after you have forgotten what you have learned.

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    John, If youre in the uk use CPC | CPC - Over 100, 000 products from one of the worlds leading distributors of electronic and related products., they stock MJ15015 at a couple of quid each. Its a trade company but they wont check if you are trade or not, If in doubt private email me and i will give you a 'friend reccomendation' as I have an account with them. (Im not trade, used to be though)
    Usually next day delivery too

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    Hmm, that was supposed to just say 'www cpc co uk' It seems to have taken on a life of its own!

  9. #9
    Senior Member Enzo's Avatar
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    The links display the page title instead of the URL itself. When you are posting and it does that, just edit the post. It won;t alter the edited text. Even though it looks different, the link should still work.
    Education is what you're left with after you have forgotten what you have learned.

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    Yes thanks. It still works as a link I just wasnt sure if you were allowed to post links? some forums dont let you.

  11. #11
    Senior Member Enzo's Avatar
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    Link all you want, it is just a feature of the BB software.
    Education is what you're left with after you have forgotten what you have learned.

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    Hi Allante666, Thanks for the input reference CPC in the UK. I do use CPC for some items however when they add on their postage and packaging/handling it takes the price up. I managed to get 10x MJ15015'sv (Motorola) from Hong Kong for 16.45 -post free, which I thought was a reasonable price. They have just arrived today and look fine. The arrival of the parts has spurred me on to finish (hopefully) the amp repairs. I'm nearly done, I only have 2 x TO-92 transistors to remove and install with new ones and the MJ15015's to install and I can test.
    I will update in any event- failure or success.
    John H.

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    yes thats true, allthough its free post an dpacking if your orders over 35 quid i believe. As you say though if you only want a few items its cheaper elsewhere.
    Hope you get it sorted, my next challenge is a humming Vox VT50, hopefully its as easy as a leaky cap. (sods law of course dictates it will be some digital anomaly unknown to man and totally untraceable)

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    Peavey XR400 (200H Power Module) Failure!

    Hi,
    I managed to obtain most specified reccommended replacements apart from transistor Q4- MPS6530 -I substituted a BC637. Got everything soldered in and gave it a test- blew fuse straight away. With the red wires disconnected from the powerboard and only the orange wires connected the pre amp/front panel red light remained illuminated.
    I then detected that there was electrical continuity between the can of C13- (5000uf smoothing capacitor) and the power transistor heat sink. The can of C14 the other 5000uf cap did not show similar continuity. The positive and negative terminals of C13 showed continuity with its can. I therefore deduced that C13 was duff. I removed both C13 and C14 and subsituted for testing a couple of 6800uf/50v general purpose capacitors. Same result blew fuse immediately.
    I am now going to check the board again and to find what is defective -may compare with original faults which I found- so the extra data may show area to look at.
    As my "workshop" is the kitchen table -I may get "evicted" from the kitchen by my better half -this may extend the time to finalise my checks . I have recorded my initial findings findings so hopefully the data may lead to success.
    John H.

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    Peavey XR400 (200H Power Module) Further Failure.

    Hi, I managed to get the amp "going" for a short period- about two minutes -then suddenly I saw that R18 (10R) was smoking and burst in flames. I switched off immediately! The 10R resistor was a replacement -it was described as having a flameproof epoxy covering. I noted that the schematic desribes this resistor as flameproof -I would have thought it would not have burst into flames. Whilst the schematic states that this resistor should be rated at 0.25W -my replacement was 0.66W (same physical size though). I removed R18 from the board -it was open. I substituted a 10R 2W. Tried switch on -and fuse blew straight away.
    I will check board again in the morning to see what else has blown and post my findings.
    John H

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    Senior Member Enzo's Avatar
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    OK, before we do anything else, please do not connect a speaker or other load until this is sorted out.

    If you do not have a variac, then PLEASE look up "light bulb limiter", then make one adn use it.

    Installing new parts, fliiping the switch to see what burns up is NOT the way to do things. And when resistorsw burn up, installing larger one won;t solve the underlying problem. Pullint a large resistor in place of a 1/4 watty one will keep IT from burning, but it will just move the burning part issue to some other part.


    The negative of one filter will be grounded, and the positive of the other filter cap will be grounded - that is normal.

    Make sure any filter caps are installed with proper polarity.

    I don;t care what has or has not been replaced, any time something goes up in smoke, get the meter out and test every transistor and diode again. New parts can easily have been damaged in the process. And remember, open resistors can damage things as easily as shoprted semiconductors.
    Education is what you're left with after you have forgotten what you have learned.

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    Peavey XR400 (200H Power Module).

    Hi Enzo,
    Thanks for the update.
    Light bulb limiter now constructed and selection of bulbs obtained 25W/60W/100W.
    Have not yet checked the board -since the last failure. Will check as soon as possible and post results.
    John H.

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    Peavey XR400 (200H Power Module) Failure & Success

    Hi Enzo,
    Managed to get a light bulb limited constructed (see pics) and obtained a selection of bulbs.
    Checked the board again but could not detect anything obvious other than the blown power transistor Q11.
    As the amp was built in 1979 I decided to replace all the electros,C7,C9,C15,C16, C17,C18. I managed to get more or less identical Nichicon spares.
    Q1 and Q2 had been replaced by 2N3904's. Q4 was eventually replaced with an MPS6530 and Q5 with a 2N3638.
    Q3 and Q9 replaced by MJE253's and Q6 with an MJE243 (or so I thought).
    Additionally all diodes had been previously replaced.
    Connected up the power board (no power transistors in place or wires connected to board) through the light bulb limiter. Filament glowed.
    Then started connecting the connectors to the board- orange wires conected -same low glow from filament.
    Then connected the red wires -initial low glow- -bright -then reduced to low glow - then conected then pre-amp board -low glow with power led illuminated on front panel.
    I then fitted the power transistors -connected through the limiter - ultra bright glow from filament!!!!!!! failure. Took apart and checked the power transistors -all ok -checked the resistors and diodes again all ok. Took out Q1,Q2 Q4 and Q5 again all OK. I was still getting a short between negative input terminal and positive input terminal. Then checked the remaining tranistors Q3,Q6 and Q9. Q3 was OK, as I removed Q6 I noticed my mistake -I had fitted the wrong type -I had fitted an MJE253 instead of an MJE243. Q9 was OK -correct MJE253 fitted. In effect I had fitted 3 x MJE253's. I clearly put this down to my dodgy eyesight. (now purchased a better illuminated magnifying lamp). Anyway, fitted Q6 correctly -connected up through the limiter -dim-bright surge and dim again- yippee! Let it run for a while -all ok and then connected directly to the mains supply- all ok -nothing getting hot and no DC at output. Assembled amp- connected with my speakers and gave it a blast with my guitar. Everything OK- no crackles in pots, reverb working ok. I also fitted a new mains lead as the original had splits in the outer sheathing. Thast is as far as I got so far -some of the chromed nuts on the pots and inputs have some light surface rust which needs removing and then the amp will look spot on- there is no damage at all to the casing. I've got some better quality smoothing caps to fit and obviously the pre-amp to look at some time.
    Thanks for your advice Enzo -and the advice to build the limiter -I really see how much of an indespansable device it is. It will certainly help in my next amp projects -restoration of some old British solid state amps. It cerainly makes a difference doing these types of restorations when there is an expert on hand to give advice/direction. Thanks again.
    John H.



  19. #19
    Senior Member Enzo's Avatar
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    Great, success is its own reward.

    Stock up on those light bulbs. The thing won;t work using CFLs.
    Education is what you're left with after you have forgotten what you have learned.

  20. #20
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    Maybe this is a dumb question in this context .... But it is the sensible question when the priority is getting something working.

    Have we called Peavey to check price and availability of a replacement PCB?

    Back to you guys and: GET A DAMN LIGHT BULB ON THE MAINS.

  21. #21
    Senior Member Enzo's Avatar
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    Not exactly sure what you are asking. But that never stopped me before...

    This amp is 25 years old, so finding a whole entire board at PV is darn unlikely.

    As someone who services amps, the only time I would consider a new board is when the old one was broken into pieces. Cracked in half, I'd fix it, but smashed into bits, then we'd find a new board. Well really a new amp.

    Emergencies are in the eye of the beholder. If you are the Van Halen tour with a concert tonight, a few hundred dollars for someone to throw what you need on a plane is no big deal. For a basement band with a demo gig this coming friday, it may be important, but if they had to shell out $200 to get a whole board here, I think they would be wiser to buy a used amp similar to what they have locally, and it will cost less. Or rent something.

    This repair has spread out over a month because each voltmeter reading takes an entire day to be interpreted. If this board crossed my bench, I'd bet my lunch money I would have nice clear music coming out of it inside of a half hour. I am not bragging, just that for a competent technician this board is a simple circuit.

    If the owner has time and no cash and is forced to repair himself, or if he just wants to learn something about servicing his own gear, regardless of the time, then buying a new board just to hurry things along doesn't serve the purpose.
    Education is what you're left with after you have forgotten what you have learned.

  22. #22
    Noodle of Reality Steve Conner's Avatar
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    Jeez! Are you sure your photographs are big enough?!
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  23. #23
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    peavy xr-400

    Hi!

    I have this same xr-400 mixer amp. It seemed completly dead, power(indicator) led didn't light up. But when i unplug the upper(upper in the 200h schematic) connector of the transformer secondary and plug the the lower which gives power to the preamp/mixer section and put on a new 2A fuse, the power led lights up when powered up and the DC voltages(about +15,5V and -15,5V) for preamp section are correct(as they are in the schematics). But every time i plug the upper transformer secondary connector to the power amp section, the fuse burns out and so the preamp and power led won't get power either.

    So the problem is somewhere in the power amp? When i measure the AC voltage in the upper transformer connector(when it's unloaded) the voltage across Red(R in the schematics) and Red(R) wire is about 69Volts. Is this correct or is there something wrong with the transformer? If transformer is ok, which components should I start checking? Do i need to take the components away from the PCB to test them?

    Any help would be great, it would be nice to get this old amp working!

    Thanks,

    l4rtt-1

  24. #24
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    Welcome to the place.

    Yes your problem is in the power amp section, and the transformer is probably ok.

    If you want help in fixing it, start a new thread and everyone will be more than glad to help you out. This thread is already finished and way too long to start a new discussion in.

  25. #25
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    Ok thanks!

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