channel loss and amp chips!!!

My best mini boomer has been playing up a little on one channel (popping every so often) but today turned her on and nothing from the left channel! tried some other speakers no good! also the wires and terminals nothing still dead!So I put a volt meter on the output from the terminals on the board and i get no volts from the left side!(not sure whether thats the way to do it).Anyhow i think it's blown the amp chip (well it is 30 years old) now is it as easy as getting one from another box which has the same amount of pins(as i have one but different make) or do i have to find a new one from somewhere!!

Like you say, it's probably a bad amp chip. Are you trying to take a measurement on the DC scale? The output won't read very high anyhow, and likely be low.

Anything on headphones?

Might be the function switch acting flakey - I had a similar 'popping' problem on my Pioneer which was attributed to the function selector solder joints.

super I did do it on DC and the voltage was very low on one (good one) and nothing on the other! It is the same on headphones and i have messed about with the selector switch ( has never been a problem before) ! sorry for these questions time and time again but i'm gonna try to learn everything to fix my machines!!

Looks like there is only 1 amp chip. You could try changing it out. But before you do, you should see if the boombox will output a normal signal from both sides via the line-outs. If you still only get 1 channel, then the issue is before the amp.

right i have check the line out and it works ok!! sooooo is it ok for me to put a chip from another box in it !!! they look the same, but one is toshiba and the box is hitachi !?I don't really know what i'm doin, but i'm not tooo bothered about the box as it's a mini but it is handy for festival and such! And i'd rather learn on this than anything else as it's easy to get to and simple also it will be a nice project to a degree!!!I would love to get a new one but not much chance of that is it!

Have you tried smacking it to get the channel back? It could be a that a break in contact developed on the circuit board over the years. Maybe it was a cold solder joint, stress to the circuit board from getting dropped, or who knows? It might also be a poorly connected speaker on the bad channel either at the speaker itself or on the circuit board. If you smack it and it works again it would tend to point to a mechanical connection issue rather than an electronic problem.

believe me i've tried that!! LOL bibox thanks for the surgestion tho

Reheat all the solder joints on and around the amp module too, they can look good at first glance but still be bad.

saxonman said:

i have check the line out and it works ok!!

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Missed that the first time through.

This is where a schematic would come in handy. Line-outs usually come from the preamp section. If that is true here (likely) it does focus the repair on the amp section. The suggestion to reflow solder on the amp chip pins is solid. Use a light touch with the iron too. You don't want to lift traces off the circuit board or you will introduce a whole new set of problems to deal with.

I have now checked all the solder joints still the same so i have removed the chip and have ordered a new one !! I found one on line for £8 quid brand new original hitachi part would you believe it!!! sooooo i will know later in the week if it's that!!!!! don't mind doin it!! so now i'm going to renew all the speaker wires and bath the whole box as well strip it down to it's bare bones!!!!! I will get this thing going whatever i have to do!! thanks for all the advice off you guys,it's forums like this which keep these box's going

saxonman said:

right i have check the line out and it works ok!! sooooo is it ok for me to put a chip from another box in it !!! they look the same, but one is toshiba and the box is hitachi !?I don't really know what i'm doin, but i'm not tooo bothered about the box as it's a mini but it is handy for festival and such! And i'd rather learn on this than anything else as it's easy to get to and simple also it will be a nice project to a degree!!!I would love to get a new one but not much chance of that is it!

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OK. So if your boombox is outputting a normal line-out signal, then the issue is 90% the amp module. I say 90% because there is still a little bit of circuitry routed between the line-out and amp. However, the amp is the primary suspect.

DO NOT put another chip from another box in it unless it's the exact same part number. Many amp modules look the same -- it's not likely they would be pin compatible. Also, unless you have sophisticated desoldering equipment, the module will probably be damaged beyond repair by the desoldering. IC's don't handle heat very well. Finally, before reinstalling the new amp chip, make sure th speaker is not shorted. If the speaker is shorted, it will burn out the new amp too.

i was thinking the volume pot if it dual or even the balance even thou they dont go bad often but that might be good to check those also,, i had a box that had a dead left channel and it turned out to be the volume slider so its always good to check those just to be sure and like norm said any part you change should be the exact part num of the part you are changing......

Superduper said:

Finally, before reinstalling the new amp chip, make sure th speaker is not shorted. If the speaker is shorted, it will burn out the new amp too.

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Great point, very few of the early chip amps had hort-circuit protection. What a b*tch that would be to go to the trouble of ordering the part only to croak it.

bibox said:

very few of the early chip amps had hort-circuit protection.

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must be an old technology, I don't think hort-circuit protection is used anymore.

MasterBlaster84 said:

bibox said:

very few of the early chip amps had hort-circuit protection.

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must be an old technology, I don't think hort-circuit protection is used anymore.

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Oops, I meant short!

like i said I'll replace all the speaker wires just to make sure even tho they look ok !! I'm gonna have to be mega quick on the resolder of the new chip to avoid over heating as I can't get anything in there to direct the heat any advice!! by the way super i have a great desolder it works so good !!I'll keep ya posted on the results once i get the chip should be later in the week!!!

oh yer nearly forgot is it best to use lead solder instead of lead free i do believe it needs a lower heat!! I have both!!

saxonman said:

I'm gonna have to be mega quick on the resolder of the new chip to avoid over heating as I can't get anything in there to direct the heat any advice!!!

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When soldering the pins, stagger them instead of going straight down the row. That will help keep heat from being too focused in one location. Of course if you can wait a bit between pins, it will help a bunch too. Just make sure the tip is well tinned before heating because it will solder much faster. A poorly tinned tip will require the connection to be heated to death.

saxonman said:

oh yer nearly forgot is it best to use lead solder instead of lead free i do believe it needs a lower heat!! I have both!!

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For hi-fi applications, I have heard that silver blend solder gives superior results. However, for lo-fi applications such as boomboxes, I think lead solder will work perfectly fine and costs a ton less too.

saxonman said:

like i said I'll replace all the speaker wires just to make sure even tho they look ok !! I'm gonna have to be mega quick on the resolder of the new chip to avoid over heating as I can't get anything in there to direct the heat any advice!! by the way super i have a great desolder it works so good !!I'll keep ya posted on the results once i get the chip should be later in the week!!!

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You want to check the speaker too. Use your meter and measure the resistance of it and compare that to the other one.