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Anyone have service manual or schematic for dead BOSE amp?!
Thanks in advance .
Regards zeoN_Rider
Anyone have service manual or schematic for dead BOSE amp?!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Thanks in advance .
Regards zeoN_Rider
No, but you can usually repair it without one.
I don't know your level of expertise so I will outline the entire fix it blind procedure for a solid state audio power amplifier built with discrete semiconductors.
It has a linear power supply, so you don't need to start there.
You will need to build a light bulb box to test your work as you go. This should be a 40W or so light bulb in series with the ac power line.
The next step is to make sure all the fuses are good and then power up the speaker through the light bulb.
The bulb should flash bright when it is first powered up, then settle to a dim glow.
If it stays bright then remove all of the output transistors and check then for dead shorts. If they are good reinstall them and check the driver transistors. After you replace the bad transistor(s) you can try powering it up again. If that doesn't do it it you should check the input transistors again for short or open.
To test the transistors all you need is an ohm meter. You will need to do all six possible connections. All the good transistors will measure the same as their like types (NPN or PNP) the bad output transistors normally show a dead short, inputs often will have an open lead.
If all the outputs, drivers and inputs are good, but it still isn't right, replace the current sources to the input stage.
Most likely is one bad output transistor. If the unit has a protection relay the light bulb will flash and go dim but the relay will not close. Repair is the same.
I don't know your level of expertise so I will outline the entire fix it blind procedure for a solid state audio power amplifier built with discrete semiconductors.
It has a linear power supply, so you don't need to start there.
You will need to build a light bulb box to test your work as you go. This should be a 40W or so light bulb in series with the ac power line.
The next step is to make sure all the fuses are good and then power up the speaker through the light bulb.
The bulb should flash bright when it is first powered up, then settle to a dim glow.
If it stays bright then remove all of the output transistors and check then for dead shorts. If they are good reinstall them and check the driver transistors. After you replace the bad transistor(s) you can try powering it up again. If that doesn't do it it you should check the input transistors again for short or open.
To test the transistors all you need is an ohm meter. You will need to do all six possible connections. All the good transistors will measure the same as their like types (NPN or PNP) the bad output transistors normally show a dead short, inputs often will have an open lead.
If all the outputs, drivers and inputs are good, but it still isn't right, replace the current sources to the input stage.
Most likely is one bad output transistor. If the unit has a protection relay the light bulb will flash and go dim but the relay will not close. Repair is the same.
The problem with classic troubleshooting is that all the voltages will be at one or the other power supply rail, with a single bad device!
Good luck.
Hi,
I am repairing one of these at present.
The fault I have found so far is an almost invisible crack in the soldered joint on one of the fifteen volt regulators.
Does anyone know if the mains power relay is controllable ?
Mine is energised all the time and the control wire does not seem to make a difference.
The analogue supplies look good ( plus and minus 40 and plus and minus 20) but all is quiet, so I guess there is a mute circuit that I have issues with.
I shall try to trace this out later tonight.
All the Best
RadioJohn
I am repairing one of these at present.
The fault I have found so far is an almost invisible crack in the soldered joint on one of the fifteen volt regulators.
Does anyone know if the mains power relay is controllable ?
Mine is energised all the time and the control wire does not seem to make a difference.
The analogue supplies look good ( plus and minus 40 and plus and minus 20) but all is quiet, so I guess there is a mute circuit that I have issues with.
I shall try to trace this out later tonight.
All the Best
RadioJohn
Hi Simon,
Thanks for the reply.
The box was scrapped by a musical instrument design lab (the UK facility of a state side organisation) I can't mention who, but you see their name on the credits of lots of feature films. The fault was low frequency instability and it was brought into our workshop for repair some years ago, but I couldn't face throwing it onto the junk pile.
I have made some progress with the electronics, I decided to trace out the power devices on the heat sink, and found that each of the three channels appears to have a bi-polar complementary arrangement with two emitters connected to the mid-point output, it has a kinda "totempole" arrangement with two more power devices to bring in the plus and minus forty rails (one top and one bottom) I haven't figured out how these two devices servo.
Most "stage amps" that I am used to seeing/repairing have just just two larger devices with small value resistors in the emitters feeding the mid point.
The DC voltage at the mid point with respect to common is a few millivolts measured on the bench DVM, that disappears when a load is connected.
I wonder if that was the DC voltage you mentioned in your post ?
The power relay eventually powers down, provided no signal is applied, but it does take a couple of minutes. If a signal is fed into the input the relay energises again. So that was a red herring.
The three amplifiers have six off 6K8 resistors that are arranged in two phases, I think they go back to the power up / protection block.
Having decided it should really work I connected an audio generator to the lead that I had removed from the damaged 5pin DIN socket, and traced the audio through to the LM351, it was at this point I decided it was "working" and that I should re-assemble the board onto the heatsink and have a test with the original loudspeakers, having spread the white compound onto the mating surfaces I put the screws back and connected the internal loudspeaker plus one of the external channels.
At this point I had a hiss - too loud to be max gain hiss, which disappeared when I connected the other L/S.
It works on all three channels but could well have an RF instability, causing distortion at particular (lowish) input signal levels.
I shall leave it for now, and have a 'scope around another day, I need to set up for a village cinema in 7.1 so will find some other means of providing my extra two channels than using a dubious Acoustimass, mine is currently an acousti-mess. ;-)
All the best
John
Thanks for the reply.
The box was scrapped by a musical instrument design lab (the UK facility of a state side organisation) I can't mention who, but you see their name on the credits of lots of feature films. The fault was low frequency instability and it was brought into our workshop for repair some years ago, but I couldn't face throwing it onto the junk pile.
I have made some progress with the electronics, I decided to trace out the power devices on the heat sink, and found that each of the three channels appears to have a bi-polar complementary arrangement with two emitters connected to the mid-point output, it has a kinda "totempole" arrangement with two more power devices to bring in the plus and minus forty rails (one top and one bottom) I haven't figured out how these two devices servo.
Most "stage amps" that I am used to seeing/repairing have just just two larger devices with small value resistors in the emitters feeding the mid point.
The DC voltage at the mid point with respect to common is a few millivolts measured on the bench DVM, that disappears when a load is connected.
I wonder if that was the DC voltage you mentioned in your post ?
The power relay eventually powers down, provided no signal is applied, but it does take a couple of minutes. If a signal is fed into the input the relay energises again. So that was a red herring.
The three amplifiers have six off 6K8 resistors that are arranged in two phases, I think they go back to the power up / protection block.
Having decided it should really work I connected an audio generator to the lead that I had removed from the damaged 5pin DIN socket, and traced the audio through to the LM351, it was at this point I decided it was "working" and that I should re-assemble the board onto the heatsink and have a test with the original loudspeakers, having spread the white compound onto the mating surfaces I put the screws back and connected the internal loudspeaker plus one of the external channels.
At this point I had a hiss - too loud to be max gain hiss, which disappeared when I connected the other L/S.
It works on all three channels but could well have an RF instability, causing distortion at particular (lowish) input signal levels.
I shall leave it for now, and have a 'scope around another day, I need to set up for a village cinema in 7.1 so will find some other means of providing my extra two channels than using a dubious Acoustimass, mine is currently an acousti-mess. ;-)
All the best
John
It seems you have it well in hand. My bet would be something simple failed and someone not quite up to it tried to fix it. Something floating in the back of my mind says bridged class H amps may be there.
Hi zeonrider,
you might find something here;
Service manual, eprom result list | ElektroTanya | Service manuals and repair tips for electronics experts
Sandy.
you might find something here;
Service manual, eprom result list | ElektroTanya | Service manuals and repair tips for electronics experts
Sandy.
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