Hey guys!
So, i got myself quite a task. Purchased a Burmester 933 amp, stated as defect, "doesn't function since some time, LED doesn't turn on". Price was good, so why not, let's give it a try. Came home, opened it up and discovered with great horror/surprise that 2 caps were missing on one side, so there was a previous repair attempt. Never a great sign, huh, of course with no disclosure from the seller. Popped in new 1.6A fast blow fuses and decided to turn it on in a bit of frustration (i understand that it is not the smartest thing to do, but what done is done). Both Power and Error lights on the front side lighted up, heard hum from inside and fuses blown after 1-2 seconds.
After a lot of googling and seeing so many clones, even especially scary ones that are basically 1:1 on the looks from the outside, i decided to send an email to Burmester to see what they can tell about this unit. Reply came back that from their information it left the factory in 1999. Cool. And then i started to look for schematics. I have spent close to 5 hours searching the most obscure websites for any hints, at the end found one on some chinese website that claimed to be of "authentic" Burmester. I will post it in that post, it is extremely sketchy, a lot of values for caps are just not stated and overall seems off. I still use it as some kind broad guideline, but won't go all the way referencing to it.
Now, to the unit itself. Disassembled bottom part and saw signs of fresh soldering. It seems to me that all caps were replaced and i am hoping that they were at least replaced with same values. Fresh solder on few transistors, though not on the output 2SA1216/2SC2922 pair. Based on the visual inspection the voltage regulators have sustained a lot of heat, so they will probably need to be replaced. There are few components without any markings between voltage regulators and output transistors, so i will definitely need some references as to what those parts are.
Since whole amp is built on one board without any connectors apart from the transformer ones, there is no possibility to disconnect stages one after another and check components in that way.
Since i heard some hum when i have turned the device on i have fear that the problem could start with the transformer. It has 4 black wires going to wall plug (important note that it could work on either 220V or 100V), 3 black wires going to one connector, 3 colored wires going to another connector and 1 colored wire going elsewhere into the board. What would be the best way to check if the transformer is faulty? Since i can't turn the device on to check voltages on the board do i need to look for the short between all those connectors one by one?
I have tried measuring output transistors without desoldering them, and get weird measurements B-C 0.52, B-E 0.045, C-E 0.52. Probably will need to desolder and check again to conclusively decide if they are dead.
Anyway, any help/advices would be of great appreciation. If someone somehow has a proper schematic it would be absolutely great as well. I will gladly take any advices on repair approaches. Is it coming down to checking every single component one by one or are there any particular spots i should point my attention first?
Thanks in advance and have a great day!
soillodge
So, i got myself quite a task. Purchased a Burmester 933 amp, stated as defect, "doesn't function since some time, LED doesn't turn on". Price was good, so why not, let's give it a try. Came home, opened it up and discovered with great horror/surprise that 2 caps were missing on one side, so there was a previous repair attempt. Never a great sign, huh, of course with no disclosure from the seller. Popped in new 1.6A fast blow fuses and decided to turn it on in a bit of frustration (i understand that it is not the smartest thing to do, but what done is done). Both Power and Error lights on the front side lighted up, heard hum from inside and fuses blown after 1-2 seconds.
After a lot of googling and seeing so many clones, even especially scary ones that are basically 1:1 on the looks from the outside, i decided to send an email to Burmester to see what they can tell about this unit. Reply came back that from their information it left the factory in 1999. Cool. And then i started to look for schematics. I have spent close to 5 hours searching the most obscure websites for any hints, at the end found one on some chinese website that claimed to be of "authentic" Burmester. I will post it in that post, it is extremely sketchy, a lot of values for caps are just not stated and overall seems off. I still use it as some kind broad guideline, but won't go all the way referencing to it.
Now, to the unit itself. Disassembled bottom part and saw signs of fresh soldering. It seems to me that all caps were replaced and i am hoping that they were at least replaced with same values. Fresh solder on few transistors, though not on the output 2SA1216/2SC2922 pair. Based on the visual inspection the voltage regulators have sustained a lot of heat, so they will probably need to be replaced. There are few components without any markings between voltage regulators and output transistors, so i will definitely need some references as to what those parts are.
Since whole amp is built on one board without any connectors apart from the transformer ones, there is no possibility to disconnect stages one after another and check components in that way.
Since i heard some hum when i have turned the device on i have fear that the problem could start with the transformer. It has 4 black wires going to wall plug (important note that it could work on either 220V or 100V), 3 black wires going to one connector, 3 colored wires going to another connector and 1 colored wire going elsewhere into the board. What would be the best way to check if the transformer is faulty? Since i can't turn the device on to check voltages on the board do i need to look for the short between all those connectors one by one?
I have tried measuring output transistors without desoldering them, and get weird measurements B-C 0.52, B-E 0.045, C-E 0.52. Probably will need to desolder and check again to conclusively decide if they are dead.
Anyway, any help/advices would be of great appreciation. If someone somehow has a proper schematic it would be absolutely great as well. I will gladly take any advices on repair approaches. Is it coming down to checking every single component one by one or are there any particular spots i should point my attention first?
Thanks in advance and have a great day!
soillodge
