Akai AA-5500 Fuse Question

damn i cant find the manual again . i am thinking its maybe capacitor coupled to the speakers and will show reading in volts at speaker terminals .
if it isn't you have problems .
will look again for manual now
 
are you sure its reading v and not mv ? .if mv that's ok . if v there is a common problem
did you power on with dbt ? if so did it dim ?
have you checked the bias ?
 
Here's a link to the service manual - it covers the 5200, 5500 and 5800 as you pointed out. http://www.hifiengine.com/manuals/akai/aa-5500.shtml

are you sure its reading v and not mv ? .if mv that's ok . if v there is a common problem
did you power on with dbt ? if so did it dim ?
have you checked the bias ?
Click to expand...

I'm pretty certain it's V not mV, the meter went overrange for anything in mV.

I powered it on with the DBT and the bulb glowed bright, then dimmed and alternated between brighter and dimmer until I turned it off.

I shall check the bias current next - is it safer to measure the voltage instead of the current and calculate the current from that (if so where would I measure the voltage?) or is it fine to connect an ammeter to the fuse terminals?
 
Ok I tried briefly measuring the current across the fuse terminals (F1 and F2) but I'm not sure if I'm damaging the multimeter - it seemed to make a click sound when I touched the terminal...

The voltage across both fuse holders is about 56V (60V is specified in the schematic). Not sure if that's relevant!
 
check voltage across emitter resistors . what wattage bulb in dbt ?
caught me at bedtime again ..but i think there are more adjustments to check in the manual ..if i am right check them but don't adjust anything yet .
will look again in morning . anyone else feel free to chirp in if you like .. i must get some sleep now its gone 1am .
 
check voltage across emitter resistors . what wattage bulb in dbt ?
caught me at bedtime again ..but i think there are more adjustments to check in the manual ..if i am right check them but don't adjust anything yet .
will look again in morning . anyone else feel free to chirp in if you like .. i must get some sleep now its gone 1am .
Click to expand...

Sorry to catch you at bedtime! I checked the voltage across the emitter resistors after the amp had been on for 10 minutes, and got:

Left:- R1: 39mV R2: 37mV
Right:- R1: 44mV R2: 46mV

If I'm correct that the emitter resistors are rated at 0.5 ohms, using V=IR this gives a bias current of:

Left:- R1: 78mA R2: 74mA
Right:- R1: 88mV R2: 92mA

The service manual says it should be idling at 40mA... :thumbsdn:

The manual gives instructions for output signal waveform and protection circuit adjustments as well as the idling current adjustment. There's also zero electrical potential adjustment but that seems to apply only to the AA-5800.

The bulb I put in the DBT was 60W, is it worth using a 100W bulb?
 
all i can suggest at the moment is check emitter resistors are measuring 0.5 ohms each .
if so try adjusting the idle current as per manual amps across fuse holder fuse removed .mark pots where set first ..turn pots very slowly . . make sure you turn the correct pots as you don't want to alter the others as you need the equipment to set correctly .
you could try 100 watt bulb in dbt to see if it stops pulsing .
 
all i can suggest at the moment is check emitter resistors are measuring 0.5 ohms each .
if so try adjusting the idle current as per manual amps across fuse holder fuse removed .mark pots where set first ..turn pots very slowly . . make sure you turn the correct pots as you don't want to alter the others as you need the equipment to set correctly .
you could try 100 watt bulb in dbt to see if it stops pulsing .
Click to expand...

I tested the resistors with the amp off and they all seem to measure about 2.0-2.5 ohms - could I be testing them wrong...?

I tried a 100W bulb in the DBT and it didn't light at all, so I tried the same 60W bulb again and it's changed completely - instead of going bright and then pulsing, it now lights dimly for a couple of seconds and then fades and seems to go out all together. Also the amp's power indicator now comes on when it's plugged into the DBT, whereas it didn't before (I assume because more current is going through). Is this good news or bad?

I'll see if I can get a direct reading on the bias and maybe try to adjust it next.
 
it seems to have fixed itself somehow .or fuses are blown or something you are not seeing .have you tried dc offset reading again now its behaving ?
ok them resistors don't seem right or its your meter .. touch meter leads together on ohms setting and see what it reads . this reading needs deducting from reading from resistor . this is assuming you got a good contact on resistors .
 
it seems to have fixed itself somehow .or fuses are blown or something you are not seeing .have you tried dc offset reading again now its behaving ?
ok them resistors don't seem right or its your meter .. touch meter leads together on ohms setting and see what it reads . this reading needs deducting from reading from resistor . this is assuming you got a good contact on resistors
Click to expand...

Checked the fuses, they're all fine. I checked the DC offset again and it's down to about 13V in the left channel after 10 minutes (it was 15V before), and 8V after 20 minutes; and 11V in the right channel after 10 mins (13V before) and 7.9V after 20 mins. A bit better than before but still pretty terrible!

The DC continues to decrease slowly even after 20 minutes, is this normal? Should I wait until it stops decreasing or does that matter?

Touching the meter leads together on ohms setting gives 1.5 ohms; 2.0Ω−1.5Ω=0.5Ω so it looks like the emitter resistors are roughly in spec...
 
ok i am suspecting some resistors have gone open or near open or transistors have gone bad . or its a bad ground ..more like a bad ground i think as its both sides . i cant remember seeing any fuse resistors marked in the manual . if there are any resistors installed like 5mm above the board that have coloured bands these are likely fuse resistors and need checking . never easy for me if it aint in front of me .even then things can be a tease .
thing that makes it harder to track down is its both channels so no reference point exept for voltage readings on schematic .
 
How would I check for a bad ground?

I can't see any resistors raised above the boards, although a lot of them are mounted vertically with a wire from the upper end running back down to the board.

Here's a pic of the left Main board:

qTakf.jpg


And the right Main board:

dA4N5.jpg


And the whole amp:

zrE1i.jpg


Don't know if these are useful! Thanks for all your help
 
they look like regular resistors to me .
there appears to be 4 replaced ones 2 on each board one looks like brown black brown .
be worth pulling the boards from sockets and clean connectors
 
I pulled the boards out and sprayed the connectors with contact cleaner, although they looked pretty good to begin with.

Here's the underside of both boards, the joints under the adjustment pots look discoloured - bad solder joint?

Left:

gMzE8.jpg


Right:

Ah7Dv.jpg
 
just thought you could check the resistors and transistors easy while boards are out . if any look wrong value in circuit you need to lift one leg on resistors and remove transistors completely or disconnect stuff they connect to .
 
Thanks I'll do that, is that just the resistance of each component? or do I need to check the voltages as well?

Also, I noticed the emitter resistors say '2W 0.5ΩK' on them and '2W 0.5Ω (K)' on the schematic - I assume that doesn't mean kilohms?
 
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