i could cry. i finally found a pretty sweet boombox ( sanyo m9840), get it home, and it produces absolutely no sound. when plugged in, everything looks like it's active according to the level meter... cassette, FM, am, everything is making the level meter move. i just plugged some headphones in, no sound out of those either. i read in another post that someone suggested hitting record on a blank tape a few times, still nothing. booo. any ideas are appreciated...

i would say if you know how open the box up and check to see if all the plugs are in on the boards,that box looks like the front panel is removable so if somebody opened it before they might not have plugged the speaker wires back in ,you never know.just make sure its not plugged in when you work on it ,you might try just flipping the switches around alot in case there is corrosion built up in them over time aside from that even if the vu meters work that only means there is a low level pre amp signal present if the amp was bad even tho signal is getting in it wont come out as sound,you might want to try to record with it too see if it picks up an audible signal.

if you are going to buy boomboxes i would suggest you buy a super long phillips screw driver you will never regret it .oh and make sure it's magnetic ,it helps alot.

hey floyd, thanks for the suggestions! i already have the case cracked open, using my handy super long philips screwdriver (one of the best purchases of my life) and everything looks to be in order, no random unplugged wires. in fact, i followed the speaker wires around, everything looks great. this box seriously looks brand new, which only makes it more frustrating. I flipped record on the cassette, and the level meters are showing when i make noise by the speakers, so again, everything working great. is there a way to replace the amp? or should i be able to have it fixed?

does it have external speaker jacks? if so that could also be the problem they corrode often and some times plugs get broke off inside the socket,if it doesnt have them then it wont be the problem .if no sound comes out with head phones i would say the amp is the likely suspec t.you can replace the amp ic chip but i would wait to see if there are other suggestions by other members that know that box better than me.or the problem in general.lol

it doesn't have any external jacks.the only jacks on it are the headphone, mic one and mic 2 jacks. i'll wait to see what others say. i can picture all sorts of voltage meters, soldering irons, and chips in my future...

man i have boxes with those same symptoms i never fixed them ,its murphy law when they look great no sound comes out .

buy a schematic......scope the chips.....only way to find the problem

well, over the past few days i've done the following things: i searched the forums for ways to get a schematic, and in a past thread someone said sanyo itself was some help, so i'm waiting to hear back from them.

i contacted a few local repair shops, most said they wouldn't touch it, but the largest one i contacted said they would fix it for 50 dollars. i'm wondering about the reliability of that estimate, as they haven't actually taken a look at the box at all, just based it off the info i told them.

so, i'm going to wait till i hear back from sanyo, but if nothing else, i'll take it to the repair shop. i guess 50 bucks repair on a 5 dollar box is a lot, but it really is a nice box.

Does line-out works with all sources ?. You need to link it to an amp. I'll guess it will work because the metters work.If it works, probably is the power stage, or the tone/volume board.
I don't know that Sanyo. Have you tried to plug some external speakers. Many boxes has the ext exp jacks soldered to the main board, so you don't need to worry about conection of the speakers. If it work, a missing connector or blown speakers or corroed disable switch (the ones inside ext sp jacks and earphone jack) may be the problem.
Both channels, when driven with only one chip ... looks like the problem were in the chip ... but you need to check other points first.
Also is easy to check if the chip works Ok.
Do you know tha part number ?.

Pedro

success,

thanks for the ideas. it doesn't have a line out, it has a headphone jack. i have tried plugging the headphone jack into some powered computer speakers i have, then turning the volume all the way up while playing a tape and radio, but it still doesn't have a signal of any kind. It doesn't have any other external speaker jacks, the only other jacks are a mic 1 and mic 2 jack. I have opened the box up a couple times now, hoping to find something that is broken or loose, but i am never sure which part i am looking for. is there a way to know what the amp chip looks like, or will i need a schematic to track it down? the only bit inside that is even remotely broken looking is a very large capacitor next to the power in on the main board that has a tiny tiny bit of light brown residue by where it is soldered in on the bottom of the board.

i took the box in today to the repair place, downtown radio of denver, and just as i thought the price i got by email was not entirely accurate, it would be $50 for the diagnostics, and then X amount for the actual repair and parts. unfortunately the girl said that since it's such an old box, the likelihood of sanyo having that exact part was next to zero, so she said i'd be better off calling sanyo first to make sure they had the part. i thought about it, and decided i'd use the cash to invest in a multimeter and see if i can get this done myself (i know a bit of soldering, not too much else) and if not, i'll just sell the box for whatever i can get. so any tips towards that end are greatly appreciated...

sorry for the length, i'm a little amped after going to the game tonight, we kicked butt.

EDIT: also, i have been trying to track down a schematic for sale for this model, no luck at all. will it even be possible to fix this without it?

Getting a multimeter is a good start. Having the schematic makes troubleshooting and repairing much easier, but its not impossible to fix electronics without one. I would start by measuring the voltages to the various boards. Since the unit powers up you know that the transformer is OK. Post pictures if you can of the various boards. The brown residue is most likely a glue, large capacitors are often glued to the circuit boards.

Leestereo-

that's what i figured on the capacitor, i just wondered because it's the only one that has it on the bottom side of the board, but then it is also the only one that is gigantor. i'll try to post some photos tomorrow, maybe you guys can help me figure out what things are what inside.

i took photos, but i'm having trouble figuring out how to embed a flickr slideshow into this site... keeps coming out as code no matter how i do it. anyway, check the slideshow out here i took a bunch of photos that don't look like they are immediately important, except maybe to see how everything links up. if you need me to point anything out in the photos, let me know.

EDIT: be sure and click the "i" in the slideshow, i added descriptions to the photos when i realized i couldn't tell what i was looking at.

I think that the brown under the cap is some kind of glue. This avoids the movement of the cap while moving the box. If the cap moves, it wil take a short time to broke its "legs" (because of the mechanical stress).
Looking the phots, seems that the amp ship is in photo 3, on the right of the record bar. It has atachaed a piece of steel (the heat sink) with 2 screws. The chip would be surrounded by 2 big caps of the same value (the speaker caps).
You can read the part number of this chip.
If sanyo had used its own chips, part number would start with "LA". For example LA4100.
But it could be from another manufacturer.

success:

Genius! i had no idea what i was looking at but what you said makes perfect sense. the chip says LA4508 3m3 and has the sanyo stamp on it. how would i test this chip to see if it's functioning or needs to be replaced? i am going to hopefully be able to get a multimeter today.

The photo is the 4, sorry by the mistake. Indeed the only chip which uses a heat sink is the power amp, so you cant get lost.
I searched the LA4508, it a 8.5 W x 2 (really powerfull).
Input form this chip are pins 2 and 13.
The simple test I do, without any instrument is touching the terminal with the finger.
That would shield lots of hum noise (60Hz or 50Hz, depending of the mains freq of your country).
It doesn't matter source position or volume. The hum wolud be heard if the chip works.
There isn't any risk of touching it.
Another simple test if that voltage on 13 and 2 would be about A HALF of the DC input (you can measure the DC input from the motor terminal for example).
Anyway, since the motor is 12VDC, I guess that DC input most be somewhere betwen 12 and 15V, that shields 6 to 7.5V on terminal 2 and 13 of the LA4508. If you read near 12V or near 0V, the chip is fried.
Please, becarefull with this pins, don't shorcut this with its neighbor pin.

Datasheet

http://www.ortodoxism.ro/datasheets/sanyo/LA4508.pdf

i touched the terminals with my finger, no noise at all on any setting or volume while powered on. i'm looking for a good place around town to pick up a multimeter. for what i am doing will a cheap analog be fine or should i invest in a more expensive digital (with cap. testing, etc etc)?

I think a cheap digital is the best option, since analog need some cares while reading regarding to the scale selecting and optical reading errors.
You don't need cap measurement capability if you are starting. Any digital 3 1/2 chinesse multimeter do the work well.

I suggest getting a digital multimeter, get probes with spring loaded hook clips (much safer to use in tight spots). Check for that the power IC is getting power by measuring the voltage between pin 7 (this is the main power amp ground) and pin 8. If you can measure voltage here then measure the voltage at the outputs: connect red probe to pin 4 and the other to pin 7, you should see half of the voltage measured between pins 7 and 8. The other output is pin 11. Post your readings and we can take it from there.

Leestereo is RIGTH, I mean measure the outputs which are 4 and 11, NOT 2 and 13 !!!!!. I made a mistake there. I need some coffe ....

quote:

Originally posted by Leestereo:
I suggest getting a digital multimeter, get probes with spring loaded hook clips (much safer to use in tight spots). Check for that the power IC is getting power by measuring the voltage between pin 7 (this is the main power amp ground) and pin 8. If you can measure voltage here then measure the voltage at the outputs: connect red probe to pin 4 and the other to pin 7, you should see half of the voltage measured between pins 7 and 8. The other output is pin 11. Post your readings and we can take it from there.

alright! i got my multimeter (and had to get a battery...stupid radio shack workers don't know crap about what they sell) and i did my measurements. i got about 13.2v coming from pin 7 to pin 8, and then when i measured 7 to 4, i got .06. pin 7 to pin 11 was .03... is this what you guys were expecting? if these readings mean the amp is blown, i found this source online that says they carry this part and will sell individual pieces for 2.75 or so. they also have the square tape belt i need for another box, so that'll save a bit on shipping too i'd imagine.

I'd say that the IC is dead. The reading of 13.2 volts means that the power supply is working as it should. The output readings should be around 6.6 volts and you're not getting anything, so the IC will have to be replaced. By the way, the easiest way I've found to remove the old part is to cut each pin close to the IC and unsolder the remaining stub. Let us know how you make out.

The chip amp is blown.
You need to do the change with some care, because you can damage tracks / pads of the cricuit board. If you don't have soldering skills practice a litlle with another board.
This IC has only one line of leads. It's quite easy to remove.
You can buy a desldoring pump, to desolder and clean pads before putting the new one.
Test the speakers before trying the new one. Use a multimeter in ohms and put the probes en each woofer terminal. You must read 3 ohms o more. Since the heaviest load the chip can drive is 3 ohms, 3 ohms reading or more is Ok. But less is bad.
The supply is checked. After soldering check each IC pad for shortcircuits (betwen neighbor pins)with a multimeter in ohms.
Becarefull with the heatsink also. Put some new Thermal Conductive Grease in the heatsink after cleaning it. Too much grease is bad also.

alright, i got the new chip in there and still nothing. i let my brother do the soldering, as he has more skill at it. we desoldered the legs, applied new grease, soldered in the new chip, i tested the readings now and it's reading the same as the old chip, channel 7-8 is at 13 i think, and channel 7-4 is at .01 or so, tiny. could it be that there is something wrong with the board that shorted the chip? i am wondering if perhaps i did something wrong with the last part, please describe how to check neighbor pins with the multimeter for short circuit? i ordered two chips from the supplier, so i have a back-up if i made a mistake (which i guess i did).

Sorry to hear that it still doesn't work. To check for shorts you can use the continuity function on the multimeter (will beep when there's a short) or just measure the resistance between the pins (a short will be whatever the resistance of the probes are). You should also check to see if there is a short between any pin and the ground (which is pin 7).

i talked it over with my brother who did the soldering- he said at one point he noticed a slight bit of pcb that was raised around the area he was soldering, i guess like it was slightly peeled back near the area he soldered. could this be either causing or indicating a further problem in this box? at this point, i feel like i could either cut it off here or be willing to work till i get this stupid thing fixed...

If the soldering pad has lifted from the board, but the trace is intact, that is ok. Did you check to see if there was a short at the speakers, which might have blown the new IC as soon as you powered up?

i did as success advised before plugging it in and checked each speaker (even the piezos...do they even matter?), all came back as 3 ohm or just slightly above. also, the metal inside the board was fine, the laquered part had lifted off a touch, just a slight bit.

also, leestereo and success, thanks again for the help. this situation is like a surgeon telling someone halfway around the world how to perform heart surgery and all the things that go with it.

It doens't matter if a pad raise from the PCB, as long as DOESN'T touch any neighbor PAD from the IC. Anyway, once you had soldered it, the pad and track cant move. But you should check (after soldering) if the conection is good. THat's follow the track wich includes the PAD wich was raised, follow the track until you reach another soldering point, Check with an ohmeter the reading betwen this point and the one who was raised, to check that it's still a continuos path.
Also check the raised against it neigbors, with an ohmeter to ensure that there isn't any shortcircuit.

I damaged a pad from my RX5600 while was soldering the record bar. I put it gently and soldered it. No problem.

A good cleaning with a toothbrush and some alcohol in the place you have soldered would be great before performing a visual check.

Good luck

You should also check the components between the IC output and the speakers. For example, the sample application circuit in the LA4508 pdf, shows a 0.15uF film cap in parallel with the speakers and if this is shorted you would blow the IC.