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Thread ID: 147406	2018-12-07 22:00:00	Electronics Experts Wanted...............Amplifiers.....	SurferJoe46 (51)	PC World Chat

Post ID	Timestamp	Content	User
1456307	2018-12-07 22:00:00	Got a Peavey Bass amplifier - MAX112 and when I start it up I get a lot of crackling and noise like distant thunder . . . . . . . in the past, I had to outwit it and just let it run it's noise game and then it worked just fine . Like I say - that was an emergency though and it was the only amp I took to play a hootch in Missoula . I have been afraid to fire it up since that time, awaiting a more convenient time to take a look for a bulged or corroded cap . No such luck! I know it's a component on the power supply - more than likely a cap that's gone bad, but I cannot find any of them bulged or leaking . Here's a schem: javascript:document . getmanual . submit() --- Well! THAT didn't work! For some reason is almost impossible for me to get as an enclosure or a PDF into this site . Let me try a different way . . . . . . . . . 9215 I think it's that pair of 2200uF caps in the power supply side of the amp PC board . I actually hate pulling components outta a circuit board and thankfully this is a single layer board with no surprises in the layers . My asking here is because I'd like a little parts-identification assistance to make this fewer teeth (my own) I have to pull without anaesthesia . Peavey was unkind enough to set the caps right next to each other on the board and then hot glue them together . Nice! I hope someone can actually open that link (^) to see it . I hadda open the pdf again and take a screenshot of it . Gack! If anyone has any experience with this sortta thing, and can point me to the most likely culprit, I'd be b'holdin' to youse guys! If anyone wants, I can send a pix of the whole amp section . . . . let me know . Well --- let me try that right now . . . . . . gotta email them to myself since they are not on this 'puter . . . . . BRB . . . . OK --- lessee if THIS works! Pix #1 --> Hmmmmm . . . "jpeg file failed to upload" I keep getting that error message from F1 .	SurferJoe46 (51)
1456308	2018-12-08 02:29:00	Don’t hold out to be an expert Joe but a couple of questions come to mind. 1: How many Speakers and Channels does this Amp handle? 2: Would the noise happen to be a 120hz hum? If there is more than one channel or speakers does the same sound come out of all of them? Just trying to confirm that the problem is probably Power Supply.	B.M. (505)
1456309	2018-12-08 09:24:00	If it was me, and a visual inspection produced no solution it's time to bite the bullet and switch it on, if you had a Variac you could try running it at a lower ac voltage to try and minimize damage. I would use an oscilloscope to track down the source of the noise after checking that the power supply rails are noise free and low ripple voltage. Start from the speaker output lead and work backwards through the audio path. My guess is it's a noisy transistor or integrated circuit, these can often be found if the oscilloscope tracing doesn't work by using "Freeze" to cool down the suspected components to zero in on the culprit. Noisy devices are often temperature sensitive, you can alternate between a can of "Freeze" and a woman's hairdryer to heat and freeze the suspected component, using a piece of toilet roll cardboard to isolate the components once you know the area. I've fixed thousands of noisy circuit boards using these techniques when I worked in the video games industry where you have a densely packed in motherboard and a noisy component somewhere on the board, sometimes no circuit diagram as well.	zqwerty (97)
1456310	2018-12-08 09:52:00	Adding to that, you might also want to inspect for cracked/dry solder joints . Intermittent connections are likely to cause intermittent noise . From your description though, I'd suspect a faulty IC or transistor too . Signal tracing etc should help you find it, like zqwerty says . I would be surprised if it was the filter capacitors . If they failed you should get hum, but probably not crackling . Can't see your attachment - try uploading relevant files somewhere else, like Dropbox .	Agent_24 (57)
1456311	2018-12-08 20:14:00	Let me see if I can post that schematic again - this time it's a png in my personal files here on this 'puter . . . . . 9224 It's a single channel with a few effects boards that even when I turn those effects OFF, the start-up crackling and distant thunder happens for about 30 seconds or so . It has a single 12 inch driver . It allows several inputs, from the instrument with and without a pad to handle pre-amped verses non-dynamic inputs (no pre-amp) . I can add-in a CD or external music or microphonic input - I don't use this function at all though . I typically play using a non-pre-amp'd guitar although I have in the past used one with a pre-amp . I know it's not 60Hz hum . Did youse guys get to see the pixs of the boards? If not - let me try that again from this 'puter this time . . . . . . . . . Either I'm getting timed-out of there's a limit to one per post . I'll try again . . . . . in a subsequent post .	SurferJoe46 (51)
1456312	2018-12-08 20:16:00	I just clicked on that last attachment I sent and got this: vBulletin Message Invalid Attachment specified . If you followed a valid link, please notify the administrator Consider it done - I'm informing the administrator . Hey Jen!!!!!!	SurferJoe46 (51)
1456313	2018-12-08 22:05:00	It would probably be more useful if you just upload the PDF to a site like Mega or Dropbox etc and post the link here. The fact it only makes noise for 30 seconds when warming up suggests a heat sensitive part probably in the power amp area where the most heat will be generated. In areas that run hot, cracked solder joints are also more likely. It would also be very helpful if you post photos of the actual circuit board(s) too.	Agent_24 (57)
1456314	2018-12-08 22:45:00	Take a look HERE (peavey.com) Could be anything it's got so many bells and whitles. :confused:	B.M. (505)
1456315	2018-12-08 23:34:00	Ohhh,a built in problem. 9225 :eek:	B.M. (505)
1456316	2018-12-09 07:16:00	Can youse guys see any of this stuff? . google . com/open?id=0B9qBBmGGFsCNVDc0TVVXbkhDMk1NVGhPaDV4T1Y1T" target="_blank">drive . google . com Ew4ZURj I suspect the two big caps that are part of the power supply to be the culprits, but I'm going to visit the solder joints too . Here's another pix on Google Drive: . google . com/open?id=0B9qBBmGGFsCNT09JYVdMOVM2c0pvTElseXNyczVKV" target="_blank">drive . google . com FNlTVFz And this is supposed to be the schematic: . google . com/open?id=0B9qBBmGGFsCNSmR4dWU1T0FyeWpzTUlyMWRHRGdPS" target="_blank">drive . google . com m9pcXJV	SurferJoe46 (51)
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