Cheesy Pyle amp hum/repair for practice project - Page 1
Forum section: electronics / projects

author: wblackledg
author_rank: Regular Contributor
timestamp: April 25, 2015, 06:59:07 pm
content: A guy at work gave me this crappy $45 amp they were using as a PA address system. He said it had developed a hum. He knew I was beginning to play around with electronics and since it was headed for the dumpster, he gave it to me to see if I could replace the cap in it.Its a pyle pca2.Brought it home, hooked it up to a speaker, with no input and it had a really loud hum. Opened it up and the 2200uF cap was plumped up so, I just happened to have a nice audio quality replacement. put it in and it still has a hum but not as bad. Strange thing, the hum decreases in volume as you increase the volume.Nothing else looked bad to the naked eye.Looked on Digikey and replacing all the small caps (4.7uF, 220uf 50V, etc.) was going to be cost prohibitive.This is really more of a learning process/project for me, but I would rather not go broke doing it.any suggestions?

author: c4757p
author_rank: Super Contributor
timestamp: April 25, 2015, 07:30:50 pm
content: What sort of caps were you looking at? They're notthatexpensive, usually.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 25, 2015, 07:46:47 pm
content: Quote from: c4757p on April 25, 2015, 07:30:50 pmindividual no, but buying them plus shipping for the entire board, it runs up.Thats why I was hoping I could figure the problem child and fix it without re-capping everything which isn't much of a learning lesson.

author: radioFlash
author_rank: Regular Contributor
timestamp: April 26, 2015, 02:44:57 am
content: Photos would be helpful. Have you checked the power rails for ripple? It's likely something like this is using a chip amp--if so, there will be a large multi-pin IC bolted onto the main heatsink (check out the LM3886 or TDA7294 as examples). If so, figure out what the chip amp is and what pins correspond to the inputs and outputs and check if you see a signal with no input.Have you tried hooking up a source to the amp? Some amps will hum or hum more if their inputs are floating. Tap around the PCB (with something plastic) and see if it has any effect on the hum--if so, there may be a broken solder joint.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 26, 2015, 03:01:53 am
content: Quote from: radioFlash on April 26, 2015, 02:44:57 amno ICs on the board. There is a Mosfet or soemthing on the heatsink.I managed to get rid of the hum unless I push the heatsink to touch the chassis. Is this due to a grounding issue?thanks.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 26, 2015, 03:08:24 am
content: Quote from: radioFlash on April 26, 2015, 02:44:57 amone of those MOSfets (if thats what it is), pins is not soldered to the board. there is no trace where the pin is, so I assume that is correct.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 26, 2015, 03:28:39 pm
content: Here are some photos.Again, it now only hums when I push on the heat sink which seems to make contact with the chassis. I replaced the 2200uf cap with the nichicon cap (large gold one). The old one was plumped up..Do I have a bad ground?thanks in advance.

author: radioFlash
author_rank: Regular Contributor
timestamp: April 26, 2015, 06:29:57 pm
content: Quote from: wblackledg on April 26, 2015, 03:28:39 pmI would check the solder joints for the heatsink and the pins of the chip attached to it, and maybe go ahead and reflow those joints. Because heatsinks are so heavy, solder joints on them, or the parts attached to them, can often fail. The chip on the heatsink is the chip amp. Try to get the part number and lookup the datasheet.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 26, 2015, 11:29:21 pm
content: Quote from: radioFlash on April 26, 2015, 06:29:57 pmthanks worked!I uploaded the video / audio file below. opening in windows media player, so you can view. I had to fake out the uploader and use a wma format.

author: radioFlash
author_rank: Regular Contributor
timestamp: April 26, 2015, 11:40:57 pm
content: Good to hear. Looking at your earlier photo, I could partially make out a label of "A2009A" for the chip on the heatsink. Based on that, I think it's using a TDA2009A chip amplifier.Datasheet:http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000127.pdf

author: wblackledg
author_rank: Regular Contributor
timestamp: April 26, 2015, 11:50:25 pm
content: Quote from: radioFlash on April 26, 2015, 11:40:57 pmcool thanks. I uploaded a short video/audio file in the post above.

author: tacojones
author_rank: Newbie
timestamp: January 13, 2016, 09:53:04 am
content: Hi. Not sure how well bumping older topics is received here. Apologies.Mine starts up with only the right channel, where the audio is overloaded (very loud), with a bit of crackle in it. It eventually pops and then both left and right channels work as expected, minus the crackle. It's intermittent, and can sometimes take an hour of continuous use before it "pops," sometimes about a minute. Sometimes a loud audio segment can seem to make it pop. I tried re-soldering the joints and pins on the chip, with no success. I'm wondering if the pots can be ruled out. Crackle makes me think of pots.Feel free to ignore this post if it's too specific.

author: tacojones
author_rank: Newbie
timestamp: January 14, 2016, 03:44:33 am
content: Quote from: 3roomlab on January 13, 2016, 12:36:47 pmI'll check that out, thanks.

author: kingofkya
author_rank: Regular Contributor
timestamp: January 14, 2016, 11:52:43 pm
content: There really bottom of the barrel parts but....http://www.taydaelectronics.com/Not the worst way to build up a stock of parts. Like common values of caps.Also you may want to look around for over heated resistors they sometime provide a clue or are the failure. Things like distorted faded paint on the bands, or any other discoloration.You might also want to look into on of theses very handy to find bad caps and cheap.(manny sellers on ebay)http://www.ebay.com/itm/Transistor-Inductance-Resistor-Tester-Capacitor-ESR-Meter-MOSFET-NPN-PNP-Detect-/331535438736?hash=item4d310d5390:g:eeUAAOSwPgxVNmKk

author: tacojones
author_rank: Newbie
timestamp: January 16, 2016, 10:22:50 am
content: Thanks very much. I actually have another one for parts - except they both have the same problem. Yeah, they're pretty cheesy. I actually like them because of the small footprint, they're cheap, and they're pretty decent for about eight months, until they crap out. I'm going to investigate the resistors (and invest in a better amp).