Strange Fuse Situation

Eldin

Active Member
So I have an Akai Aa-810 i'm working on (service manual is non existent). The left channel works for a while then gets random power surges (could see the fuse swaying) and then it just blows. Any help? Thanks
 
Never seen one so going by the symptoms.

Is it discrete outputs or power packs?

It reminds me of a bad bias system.
If it uses a thermistor, that may be flaky.
Is there a blob type thing on the heat sink?

It may be a flacky driver or pre-driver transistor.

Start using a dim bulb tester to save fuses.
Start checking voltages side to side.
Hopefully you can match parts one side to the other to see if voltages match. Do this on a dim bulb tester. Look for places on the bad side where voltages are not matching the good side.
 
There are two but they are near it, not on it. IT uses discrete outputs (if by that you mean induvidual transistors). I replaced most of the transistors on the amplifier board because just about all of them were known to be problematic (doing this cured by bad left channel early on). How would I go about fixing the bias if that would be the problem? I just can't find a manual for this thing so it makes it all that more exciting :crazy:
 
Currently unavailable to download? Something related to server issues .-. The fuse that goes to the left channel. Not one of the power fuses but the 1.5A fuse. It's so strange. The channel sounds fine while listening to but over a bit of time it starts to present audible power surges, then the fuse blows.
 
It still blew without a speaker attached. Just tested that. Mind you it still didn't instant blow. It blew after a bit of time. My best guess is a thermistor or something overheating somewhere. I just don't know what it could be
 
Currently unavailable to download? Something related to server issues .-. The fuse that goes to the left channel. Not one of the power fuses but the 1.5A fuse. It's so strange. The channel sounds fine while listening to but over a bit of time it starts to present audible power surges, then the fuse blows.
First entry at top of list - NO affiliation other than being satisfied customer
http://www.stereomanuals.com/man/rep/akai/akai_manuals_aa-810_xx.htm
 
It still blew without a speaker attached. Just tested that. Mind you it still didn't instant blow. It blew after a bit of time. My best guess is a thermistor or something overheating somewhere. I just don't know what it could be
wont be a speaker fuse then . maybe its the rail fuse for that bad channel .
 
Not sure. I don't think the output transistors are getting too hot because the right channel maintains normal operation. Upon checking dc offset I got 18vdc (not a typo) on the bad channel. I can double check when I get home.
 
p.s i had an amp doing just about same thing . it was a long time ago now and my memory is bad . the fuse wire was dancing to the music then pop .
i do seem to remember it was incorrect rating or it was fast blow i used instead of slow blow . will report back if i remember fully .
you could see whats written on the other channels fuse ..if it has a T its time delay or slow blow ..others call them motor rated .
 
Hey that's why i'm asking here, I know there is something wrong just no idea what it could be. My best guess so far is a thermistor failing once it warms up. Allowing too much power to go through maybe?
 
Hey that's why i'm asking here, I know there is something wrong just no idea what it could be. My best guess so far is a thermistor failing once it warms up. Allowing too much power to go through maybe?
That's why you need a schematic and a DVOM at minimum
Fuses blow for one of two reasons
They "see" a current or a voltage that exceeds their rating, OR a short
You need to determine where the problem is using a schematic and checking voltages
A PTC (Positive Temperature Coefficient), if it were equipped with one (highly unlikely but I'll never say never), would reset after the receiver cooled down, not cause a fixed value fuse to blow
You have a basic power supply, power amp, pre-amp transistor or short problem
Even possible you have a thermal problem with an output device (another unlikely but never say never)
A schematic (which I don't have) will help you to eliminate all of the "could bes" and allow you to focus your diagnosis in a more meaningful way rather than guessing
 
I'm still trying to locate a schematic. I don't think it could be a short right? The fuse visibly slowly bent and blew. I'll try to add a few pics when I get home to see if that helps understanding. This thing was butchered at some point (someone replaced the output transistors without reattaching them to the heat sink:thumbsdown:) I started using my multimeter to compare channels (measurments here vs there) but i had to leave.
 
I'm still trying to locate a schematic. I don't think it could be a short right? The fuse visibly slowly bent and blew. I'll try to add a few pics when I get home to see if that helps understanding. This thing was butchered at some point (someone replaced the output transistors without reattaching them to the heat sink:thumbsdown:) I started using my multimeter to compare channels (measurments here vs there) but i had to leave.
I gave you the link to a manual with schematics in post #8
19 bucks + 3 bucks for First Class Mail
 
That's why you need a schematic and a DVOM at minimum
Fuses blow for one of two reasons
They "see" a current or a voltage that exceeds their rating, OR a short
You need to determine where the problem is using a schematic and checking voltages
A PTC (Positive Temperature Coefficient), if it were equipped with one (highly unlikely but I'll never say never), would reset after the receiver cooled down, not cause a fixed value fuse to blow
You have a basic power supply, power amp, pre-amp transistor or short problem
Even possible you have a thermal problem with an output device (another unlikely but never say never)
A schematic (which I don't have) will help you to eliminate all of the "could bes" and allow you to focus your diagnosis in a more meaningful way rather than guessing

Ditto.
 
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