aiwa 660 volume problem

[Superduper]

Hmm, I could not find a datasheet on your Toshiba amp module so I can't help you there. The red wires are A/C so 13 volts is probably correct. I presume this is a 8 cell boombox? That means it's normal voltage should be 12 volts. The power out to your PCB should not be anywhere near 32volts so you've probably made a mistake. Make sure your tester is set to the correct scale and on DC. Check it again. If you are getting anything close to 32volts, I'd say your PCB is toast. Perhaps you meant to say 12 volts?

 

[Eric]

What voltage are you getting across that large capacitor? Should be around 12 - 15 volts dc. This is what should be going into your main board. Did you ever get it to run on batteries? This might help isolate power issues from Amp issues.........maybe

 

[blah blah]

norm it really measured 32V, i had it set to the same scale as when i got the 13v from the red power supply output lines. i actually just blew the fuse in my meter though as when i did recheck i had it on on dc voltage and i was checking on ac. doesn't sound good for the pcb if that reading is correct though? i don't see any visual damage of any sort...anything to look for?

eric i couldn't check the large capacitor reading since i blew my fuse in my multimeter, possibly that was the problem to begin with. will check it tomorrow though. I did try it on fresh batteries last night and it seemed to fry whatever was ailing it, at low volumes on ac it sounded great and only blew out on +5, after i tried the batteries the speakers just pop and snap....weird, the ac operation was nothing but speaker pops after that.

i hope you guys hang with me on this thread a bit, i really appreciate the help!
i think i can work it out unless the pcb is fried :'-(

 

[Superduper]

No. Something is not right with the measurements. If you are saying that the voltage going to the PS board from the transformer is 13v a/c, you can't get to 32v DC from there unless there is a step up transformer or some form of DC to DC converter. The only thing that the PS board does is (1) rectify the A/C to DC and (2) perform the switching from A/C-in to DC-in to BAT-in and (3) Filter the output by means of the large filter capacity. Failure of any of those features does not increase the voltage. However, if the input voltage switching is performed on the board and there is something screwed up there, such as a short, or miswired connections, then I could see how that might be a possibility. I presume that the yellow/white/black wires go the the power transformer? Then those might be the transformer primaries and if you truly are getting 32volts, there is a very good chance that significant component failures exist on the main PCB. Transistors, resistors, diodes, etc can tolerate fairly high voltages but not current. Increasing the voltage by 300% will increase the current consumed by 300% as well, if impedance remains the same. Also, capacitors can get damaged/explode if exposed to voltages outside the range of their rating. The biggest problem will be the IC's such as the power amp modules. Most have a fairly small operational voltage limit and I would guess that your amp is rated at 15-16 volts max.

 

[blah blah]

norm you are indeed correct! I believe my misreading is a result of having my meter set to a/c not dc when measuring the the +dc -dc going into the PCB board. i has 32 a/c but was supposed to be measuring dc! i will recheck tomorrow when i get a new fuse for my multimeter. your explanation regarding PS board function made my mistake clear once i dug down and saw the labels for dc.

this does have input voltage switching on the PS board but was set correctly, not sure if wired correctly but once i re-test with the correct dc setting, i will know.

it will probably end up being a loose wire somewhere else. the guy i got it from was obviously inside due to the wild arrangement and tangles of wire and cracked board

again thanks for the great advice and for passing along some wisdom to a fellow enthusiast.

 

[blah blah]

norm- the reading going in to the main PCB is 15V dc. frustrating giving advice to a person with the wrong setting!

so i guess power supply is ok. would you think i should check the readings on the amp chip even though i don't have specs to see if something is just dead?

 

[monchito]

well i am happy to see only 15v i was about to have box attack norm i was thinking that maybe a bad volume pot low volume ok until you get to the bad spot then it not working correctly and thats only a possibility maybe.....

 

[Superduper]

Sorry I can't be of more help. So many issues and distractions on my mind lately I think I'm burned out. Only thing I can think of that would be simple is maybe the function selector but I think BlahBlah said he already deoxit'd everything.

Blah Blah, are you getting 15v at the circuit board with the radio operating? Sometimes, a weak PS can show 15v with everything off but craps out with any kind of a load. Well, anyway, there is just so many different possibilities I don't know where to begin. Where are you located? Maybe another member close by with a little bit more technical ability can look at it for you?

 

[monchito]

Sorry I can't be of more help. So many issues and distractions on my mind lately I think I'm burned out. Only thing I can think of that would be simple is maybe the function selector but I think BlahBlah said he already deoxit'd everything.

Blah Blah, are you getting 15v at the circuit board with the radio operating? Sometimes, a weak PS can show 15v with everything off but craps out with any kind of a load. Well, anyway, there is just so many different possibilities I don't know where to begin. Where are you located? Maybe another member close by with a little bit more technical ability can look at it for you?

norm a weak transformer ,but still so much could be wrong i have seen with just a recap takes care of most problems right away... take care my good friend ...

 

[blah blah]

Norm and Monchito- No problem guys i appreciate all the input and suggestions . i will let you know if i discover a solution. if the box is even powered up on radio the speakers just pop and pop. must be a short or as monchito suggested a cap problem. I am in utah so pretty isolated will update if i get anywhere. thanks again, this is the best thing about this site.