Akai AA-5500 Fuse Question

M

mallardice

New Member
I recently bought an Akai AA-5500 integrated amp which is dead in the left channel. The protector fuse that feeds the left Main Amp board is blown, and is rated at 4A 125V, but there is no indication of whether it is slow-blow, fast-blow, normal, etc.

There are no letters on the holder, and the service manual/schematic only specifies the amp rating. The other (intact) fuse for the right channel looks like it has one straight filament with another one wound around it.

The blown fuse is a SOC ST2, which isn't listed in the SOC catalogue, but all the other SOC ST fuses listed (ST3-ST6) are described as 'inrush-withstand'. This suggests a slow fuse to me, but would it be rated T or TT (or M, F, etc.)?

Many thanks!
 
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Thank you! The fuses are on the way, and I've built a dim bulb tester following the numerous sites and threads that mention it. However, I'm relatively inexperienced when it comes to wiring so I thought I'd make sure I've got this right - does this look correct?

http://i.imgur.com/GbSHM.jpg

This is using UK plugs and sockets but I assume the principle is the same as elsewhere.
 
if the earth pin is at bottom of pic in socket swap the blue wires if at top its good to go assuming the brown to plug is live
 
Dim bulb test looked ok (bulb lit bright for a second then dimmed), so I powered it up and the Protector light came on. Switched it off and back on again and it's been fine ever since, both channels working. The Protector light has come on once more since, but when I turned it off and back on it was fine again. Is this a sign of an impending component failure?
 
Well the fuse blew again, so I assume there's a failed component somewhere. Any ideas for troubleshooting this? This is my first attempt at fixing electronics so I'm not entirely sure what to look for.

Does the fact it's the fuse serving the left Main Amp board mean the fault is on that board?

Thanks
 
first check the output transistors for shorts .tr1/2 ..then tr4/7 it looks like there is 2 fuses one for + and one for - .. not too relevant though as you need to test all them transistors first .then depending if any are short its a matter of working out what else will have stressed and needs checking .
service manual here that's easy to read ..http://www.hifiengine.com/manuals/akai/aa-5500.shtml
free sign up ..
 
first check the output transistors for shorts .tr1/2 ..then tr4/7 it looks like there is 2 fuses one for + and one for - .. not too relevant though as you need to test all them transistors first .then depending if any are short its a matter of working out what else will have stressed and needs checking .
Click to expand...

I checked the output transistors according to this thread using what looks like the diode function on a multimeter, and got the following results - which would suggest all the transistors are failed in various ways. The meter seems to use '1.' to indicate no conduction.

cn3fj.jpg


Are the results realistic or is it worth removing the transistors and testing them out of circuit? I identified the base as the wire on the left and the emitter as the brown wire on the right on the back of the transistors:

HEmfB.jpg


Is this correct?
 
these look like you tested in circuit .. none appear shorted though . so should be ok to power up .
something is blowing the fuse though i will look at schematic again to see what to check next .
in the meantime pull the transistors and retest out of circuit to be sure they are ok .
do them one by one so they go back where they came from ..also check the fuse holder is holding the fuse tight and soldered in solid .a bad connection here will melt the fuse .rather than blow it .
i cant see anything that would take out a 4amp fuse without first burning up is maybe shorted speaker connection as the transistors don't appear shorted .which one of the fuses blew ? or was it both for left channel ?
 
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There are just two fuses apart from the main fuse on the back, one connected to the left Main board and one to the right (I think), and named F1 and F2 in the schematic. The main fuse is named F5, but F3/4 don't seem to exist either in the amp or on the schematic. F1 is the fuse that's blown twice, the others are still intact. The holder seems tight and I can't see signs of a bad connection.

These are F1 and F2, on the underside of the amp, with the Main board connections top and bottom right:

bDVPw.jpg
 
ok i see the confusion ..the manual i have covers the 5800 5500 and 5200.
i am guessing its the positive side that's fused then .
 
ok i am now looking at correct diagram .
i think you need to compare voltages on main amp boards to try and track it down
. junctions 2 .4 .5 .and 7 . referenced to chassis ground
 
Any idea what could have caused it?

i cant see anything that would take out a 4amp fuse without first burning up is maybe shorted speaker connection as the transistors don't appear shorted .
Click to expand...

Do you mean a short between the speaker wires or something internal?

Thanks
 
i think you need to compare voltages on main amp boards to try and track it down . junctions 2 .4 .5 .and 7 . referenced to chassis ground
Click to expand...

Could you explain the procedure for doing this with a multimeter? What kind of readings should I be looking for?
 
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60v at fuse or collector tr1 / 27.5v at terminal 4 or base of tr1/ 27v at terminal 5 and 6 / . all referenced to chassis ground .
that should keep you busy for a while .
there are more voltages as well as these on the schematic .
 
60v at fuse or collector tr1 / 27.5v at terminal 4 or base of tr1/ 27v at terminal 5 and 6 / . all referenced to chassis ground .
that should keep you busy for a while .
there are more voltages as well as these on the schematic .
Click to expand...

I haven't tried this yet as I've been busy for a while, but I'm ready to give it a go now. I'm pretty new to all this - I assume the amp has to be powered up while doing these voltage tests (and therefore a new fuse put in), should I plug it into the DBT?

Thanks!
 
Update

I put a new fuse in, powered up the amp and tested junctions 1-8 on both Main boards, and compared them with the values on the schematic:

SYgCB.jpg


Am I right in thinking these all look pretty much OK?

However, I also tested the DC offset at the speaker terminals according to the sticky - and after letting each channel settle for 10 minutes or so, got about 15V in the left and 13V in the right!

This seems very unrealistic - am I doing something wrong or is this a symptom of a serious fault?
 
Anyone know what my next move should be? Does the very high DC at the speaker terminals mean some of the transistors on the Main boards are bad, or could it be something else entirely?

Any info appreciated!

Thank you
 
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