HI,
Trying to repair my boy’s Mitsubishi da-a10 amplifier.
Can anyone help me with a service manual and schematic?
Have looked on line and don't seem to find one to down load or buy?
This was a very good sounding amp and would like to repair it.
The right channel works OK, the left works at the very lowest input. When I turn it up the channel drops out until I cycle the AC power. The voltage on right rail to the power transistors case shows -59 volts, the left bad channel show -45 volts on the same test point. Each channel looks to be in two parts for the power transistors?
I have worked on my Ham Radios for 30 years but this is a different type of amplifier with lots of control.
So can anyone help me out?
Thanks Terry in North Dakota
Trying to repair my boy’s Mitsubishi da-a10 amplifier.
Can anyone help me with a service manual and schematic?
Have looked on line and don't seem to find one to down load or buy?
This was a very good sounding amp and would like to repair it.
The right channel works OK, the left works at the very lowest input. When I turn it up the channel drops out until I cycle the AC power. The voltage on right rail to the power transistors case shows -59 volts, the left bad channel show -45 volts on the same test point. Each channel looks to be in two parts for the power transistors?
I have worked on my Ham Radios for 30 years but this is a different type of amplifier with lots of control.
So can anyone help me out?
Thanks Terry in North Dakota
Did some more checking..........
Just compared the rectifier bridge from the right to the left channels. One pair of the bad channel diodes shows -45V with one pair showing -58V. On the good channel I have -58V on all 4 diodes. Might be a cap pulling down for my first thought, but to be two caps doing the same? Sure could use a schematic or service manual. Anyone have one?
Terry in North Dakota
Just compared the rectifier bridge from the right to the left channels. One pair of the bad channel diodes shows -45V with one pair showing -58V. On the good channel I have -58V on all 4 diodes. Might be a cap pulling down for my first thought, but to be two caps doing the same? Sure could use a schematic or service manual. Anyone have one?
Terry in North Dakota
Mitsubishi DA-A10DC Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
In German but the schematic is fine.
In German but the schematic is fine.
riotpack, tnx fer link to schematic.
I am down to the Diode 12 being pulled down to -44V complared to the other channel of -58V. So now what is doing that? I always look for a cap first? Enough for tonight.
I am down to the Diode 12 being pulled down to -44V complared to the other channel of -58V. So now what is doing that? I always look for a cap first? Enough for tonight.
One of the first places I would check would be the bridge rectifier since there is a separate rectifier and transformer for each channel. It is not uncommon for a bridge to fail partial short or one of the diodes to go completely open - which could explain the low voltage and the other behavior you have seen.
Measure the transformer secondary AC voltage at each bridge - if they are nearly identical the culprit will be the bridge, if the voltage is much lower this indicates there is a high current fault on that channel and further investigation is required. (It could be a partial short in the bridge or something worse.) If it is missing on one side or the other of the bridge it is probable the transformer has an open winding - this is fairly unusual in low voltage transformers. This list is not all inclusive..
If you get this amp sorted out it is time to replace the electrolytic caps. I remember these amps and this one is probably close to 30yrs old now.
Measure the transformer secondary AC voltage at each bridge - if they are nearly identical the culprit will be the bridge, if the voltage is much lower this indicates there is a high current fault on that channel and further investigation is required. (It could be a partial short in the bridge or something worse.) If it is missing on one side or the other of the bridge it is probable the transformer has an open winding - this is fairly unusual in low voltage transformers. This list is not all inclusive..
If you get this amp sorted out it is time to replace the electrolytic caps. I remember these amps and this one is probably close to 30yrs old now.
Does a relay click and both channels drop out when it happens? Or only the damaged channel and the other continues to work fine?
Test the AC output of the transformer then Desolder the leads to the bridge and test the individual diodes, also while disconnected test the output of the transformer again to see if it changes.
If something was loading it down dropping the rail by 14 volts it would get pretty hot so it may be an open diode. You mention -44 on the bad channel and -58 on the good one. What is the voltages on the other two output transistors (on the positive rail)?
Test the AC output of the transformer then Desolder the leads to the bridge and test the individual diodes, also while disconnected test the output of the transformer again to see if it changes.
If something was loading it down dropping the rail by 14 volts it would get pretty hot so it may be an open diode. You mention -44 on the bad channel and -58 on the good one. What is the voltages on the other two output transistors (on the positive rail)?
Kevinkr and riotpack
Thanks for the reply and help here. I am new on this form and forms for that matter. Both transformers have the 58 volts. I checked the bridge for the right channel and have +58 on 2 diodes and -58 on the other 2 diodes. Then on the left channel I have the +58 on 2 diodes but -44 on 2 diodes. I could see this and you helped me confirm it. It might be only 1 diode out of the low -44Volts. I will have to remove the diode. It is special package with the 2 diode and a heat sink. Will test them out of the board with the fluke.
The relay clicks after power is on a couple seconds. Only the damaged left channel drops out, the right keeps playing if I remember correct. Will check again when I get the left channel bridge repaired.
I was thinking a bad cap might be pulling down the –voltage side of the bridge, wasn’t thinking that only 1 of the 2 diodes out could drop the voltage about the 14 volts or so low.
Will get back when I find out some more. Thanks so much from the help. I enjoy working on amps but mostly old tube ham radio RF amps. Again thanks from Teran in North Dakota
Thanks for the reply and help here. I am new on this form and forms for that matter. Both transformers have the 58 volts. I checked the bridge for the right channel and have +58 on 2 diodes and -58 on the other 2 diodes. Then on the left channel I have the +58 on 2 diodes but -44 on 2 diodes. I could see this and you helped me confirm it. It might be only 1 diode out of the low -44Volts. I will have to remove the diode. It is special package with the 2 diode and a heat sink. Will test them out of the board with the fluke.
The relay clicks after power is on a couple seconds. Only the damaged left channel drops out, the right keeps playing if I remember correct. Will check again when I get the left channel bridge repaired.
I was thinking a bad cap might be pulling down the –voltage side of the bridge, wasn’t thinking that only 1 of the 2 diodes out could drop the voltage about the 14 volts or so low.
Will get back when I find out some more. Thanks so much from the help. I enjoy working on amps but mostly old tube ham radio RF amps. Again thanks from Teran in North Dakota
keep in mind that beyond the rectifier or diode pack either as you said it could be a capacitor issue that doesn't ""bring up ''' the voltage
in the weird case that you have more than one trouble wild guess can be a blown output transistor together with a dead capacitor that cannot produce power enough to blow the fuse this will also come with excessive heat somewhere so it will be easy to trace .
Did you notice excessive heat somewhere ? look at that also ...
Remark about capacitors is a must and all of them will need to be replaced ( small ones are by far more important to replace than the big ones )
in the weird case that you have more than one trouble wild guess can be a blown output transistor together with a dead capacitor that cannot produce power enough to blow the fuse this will also come with excessive heat somewhere so it will be easy to trace .
Did you notice excessive heat somewhere ? look at that also ...
Remark about capacitors is a must and all of them will need to be replaced ( small ones are by far more important to replace than the big ones )
OK, unsoldered the bridge diode and checked on my Fluke 87 to see it looks OK. Installed a couple new diode rectifirers. Still same voltage. Pulled the bad channel 4X power transistors and checked the voltage agian to find it still pulled low to -45V. the + side is at +57V. The good channel has + - 57 on all 4 diodes. Something is pulling the minus side down. When I power up the amp I get -50V untill the speaker relay kicks in,then it drops to -45V. I will try putting drive to the bad channel into the 8 ohm dummy load to see if it drops lower before it trips out and I have cycle AC power to bring it back up. It is looking more like a cap pulling it down. I am lost as where to start looking now? I don't smell or find anything hot? Hate to just shotgun the caps. Will think on it for a day and see if any more ideas are posted. Thanks Teran in North Dakota
Can you check C11 isn't open, or put a scope on that bad rail and check for excessive ripple? 58x.707 is around 41v which is around what you would measure if the filter cap had a high ESR or was open, I would expect a hum on the channel. Also look for dry joints around the PSU area. How are the terminals attached to those caps?
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Riotpack
Thanks for the tips on C11. I don’t do much of this type of trouble shooting so need all the help I can get HI HI. Having 2 channels is nice to do comparisons. Scope shows nice sign wave on the working channel and D11 of the bad channel. D12 shows a very spiked and choppy sign wave(saw tooth). Then I remembered to look at D12 with my Fluke in DC to get -45Volts, Then going to AC I get 8.5Volts AC! The good channel shows only a few mill volts AC. I see that C11 is 60 Volt- 10,000uf cap. I don’t have anything like that to sub in line to test the channel. Does this point to C11 not filtering the AC after the bridge diodes rectify it. Possibly pulling down the voltage from -58 to -45volts? I don’t know how to check any more without replacing the C11 cap. Now what? Thanks so much for the help with this amp I am learning lots about this amp from you and this form. Teran in North Dakota.
Thanks for the tips on C11. I don’t do much of this type of trouble shooting so need all the help I can get HI HI. Having 2 channels is nice to do comparisons. Scope shows nice sign wave on the working channel and D11 of the bad channel. D12 shows a very spiked and choppy sign wave(saw tooth). Then I remembered to look at D12 with my Fluke in DC to get -45Volts, Then going to AC I get 8.5Volts AC! The good channel shows only a few mill volts AC. I see that C11 is 60 Volt- 10,000uf cap. I don’t have anything like that to sub in line to test the channel. Does this point to C11 not filtering the AC after the bridge diodes rectify it. Possibly pulling down the voltage from -58 to -45volts? I don’t know how to check any more without replacing the C11 cap. Now what? Thanks so much for the help with this amp I am learning lots about this amp from you and this form. Teran in North Dakota.
Can you test the DC ripple directly on the cap to make sure it isn't simply a high resistance connection to the cap? it looks like there are two caps per cylinder package. Take a photo of the wires going to the cap, or note them down, and remove the cap and you can test it, a crude test would be a time constant test Capacitance and Uses of Capacitors
The caps are 10,000uF so 0.01 Farad. If you put a 1000 ohm resistor in series with the cap and apply 9 volts, you should get 5.7volts across the capacitor after 10 seconds (RxC) and 7.8V after 20 seconds (place a voltmeter directly across the cap and charge through a 1K res).
After 5 time cycles (50 seconds) we can say the cap is fully charged to 9V which would be 50 seconds. Now if you short the cap through the resistor, after 10 seconds the voltage should be 3.3V. This will not test ESR but will give you a rough idea if it is charging to its capacity, I would replace it anyway.
Remember this capacitor has two actual capacitors inside it, 3 pins, one is common to both caps. Test both capacitors (inside the single package, not the otehr channels cap) and compare readings. Make sure you get the polarity correct or it may explode.
The caps are 10,000uF so 0.01 Farad. If you put a 1000 ohm resistor in series with the cap and apply 9 volts, you should get 5.7volts across the capacitor after 10 seconds (RxC) and 7.8V after 20 seconds (place a voltmeter directly across the cap and charge through a 1K res).
After 5 time cycles (50 seconds) we can say the cap is fully charged to 9V which would be 50 seconds. Now if you short the cap through the resistor, after 10 seconds the voltage should be 3.3V. This will not test ESR but will give you a rough idea if it is charging to its capacity, I would replace it anyway.
Remember this capacitor has two actual capacitors inside it, 3 pins, one is common to both caps. Test both capacitors (inside the single package, not the otehr channels cap) and compare readings. Make sure you get the polarity correct or it may explode.
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Another test is the leakage test, where you put an ammeter in series with the discharged cap and the battery. The flowing current should start high (AMPS) and quickly fall to a very low value (a couple of milliamps) - If the flow rate doesn't go right down to milliamps and keeps flowing at tens or hundreds of milliamps then the capacitor is leaky.
Riotpack,
Just did a test of the C11 cap. I don’t have a correct cap to try but did put in a smaller sub and the -45 volts came right up to -58 and the trace looked good on the scope. So I think I need to recap this amp.
I don’t seem to find any dual 10000uf 60 volt caps. Not sure what to use or where to buy? I do want to get it up and run it for awhile before I recap it.
Any ideas from you or anyone on what to do about the C11 dual cap would be great. I am thinking to buy a single stage cap in 10000uf at 63 volts to start with. I might be able to tuck it in for some testing.
In the ham world with the old tube radios I would leave the old cap in place for looks and place the new under the chassis. Maybe not room with this amp. I have also placed 2 caps into the old cap tube. Guess I will have to remove the original and see what I am looking at as it has the black can cover over it.
Wish I had a cap to try and put a load on the amp to see if the channel still drops out?
Thanks for the help, will get back on here when I find parts and run the amp with a load.
Teran in North Dakota
Just did a test of the C11 cap. I don’t have a correct cap to try but did put in a smaller sub and the -45 volts came right up to -58 and the trace looked good on the scope. So I think I need to recap this amp.
I don’t seem to find any dual 10000uf 60 volt caps. Not sure what to use or where to buy? I do want to get it up and run it for awhile before I recap it.
Any ideas from you or anyone on what to do about the C11 dual cap would be great. I am thinking to buy a single stage cap in 10000uf at 63 volts to start with. I might be able to tuck it in for some testing.
In the ham world with the old tube radios I would leave the old cap in place for looks and place the new under the chassis. Maybe not room with this amp. I have also placed 2 caps into the old cap tube. Guess I will have to remove the original and see what I am looking at as it has the black can cover over it.
Wish I had a cap to try and put a load on the amp to see if the channel still drops out?
Thanks for the help, will get back on here when I find parts and run the amp with a load.
Teran in North Dakota
riotpack,
I also enjoyed reading on the cap web page you posted. Lots of good reading.
Teran in ND
I also enjoyed reading on the cap web page you posted. Lots of good reading.
Teran in ND
Well even without a substitute cap you know there is a problem and how to fix it so this should be done, and there is a very good chance all will be solved. In regards to finding a replacement, if you can fit say one in the chassis and one in the hollowed out old cap then by all means do it. Just make sure the capacitors are mounted away from the main heat sink and transformer. There are caps somewhere out there that are dual, but are expensive, and not required if you use a couple of single 10000uf caps. Most websites will tell you the dimensions so time to see what can be shoehorned in there I guess.
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OK, will see what I can come up with replacing the cap. Thanks for the help, I learned a lot on this one. Most I have used a scope in long time. Even had to think back to the theory I learned 30 years ago HI HI.............tnx and 73 KFØHR Teran in North Dakota
If it is still not working, the protection circuit might be the problem.
When you power on the Amp, it is supposed to make a "Tick" after about 5-8 seconds. If another "Tick" is heard afterwards, that means that the amplifier went into protection mode. And there is the problem.
The problem is caused by the two audio sides to be unbalanced and it might just be a difference of a couple of mV.
To solve this, you want to do the Idling Current Adjustment. This is found in the service manual. I recommend you use this Service Manual as it is in english and has all the schematics and procedures to help you along the way.
You'll have to adjust two variable resistances so that you gauge the voltage correctly for the protection circuit.
If you open the bottom panel of your DA-A10, you'll find the bottom of the main circuit, and you'll stop right there as the variable resistance access point is on the underside of the main circuit board. you'll find to holes that are about the same lateral position on the board, in which you should be able to see a flat screw head. These are VR103 and VR203, the current adjusting variable resistances.
Download the manual, the procedure is on page 15.
If you have any other questions let me know. I would also consider doing this test even if you don't hear the "Ticks", just in case.
Cheers !
When you power on the Amp, it is supposed to make a "Tick" after about 5-8 seconds. If another "Tick" is heard afterwards, that means that the amplifier went into protection mode. And there is the problem.
The problem is caused by the two audio sides to be unbalanced and it might just be a difference of a couple of mV.
To solve this, you want to do the Idling Current Adjustment. This is found in the service manual. I recommend you use this Service Manual as it is in english and has all the schematics and procedures to help you along the way.
You'll have to adjust two variable resistances so that you gauge the voltage correctly for the protection circuit.
If you open the bottom panel of your DA-A10, you'll find the bottom of the main circuit, and you'll stop right there as the variable resistance access point is on the underside of the main circuit board. you'll find to holes that are about the same lateral position on the board, in which you should be able to see a flat screw head. These are VR103 and VR203, the current adjusting variable resistances.
Download the manual, the procedure is on page 15.
If you have any other questions let me know. I would also consider doing this test even if you don't hear the "Ticks", just in case.
Cheers !
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