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KrisBlueNZ
Sadly passed away in 2015
Haha, that's great Pete! I would cover all of it, apart from the fusible resistor, in hot melt glue or similar, to give it some structural strength and prevent it from touching other parts. But you've got it, and you even replaced the bicolour LED with two red ones in anti-parallel. I thought you said you were a novice!
OK, do you have a multimeter? What make and model?
You can start by measuring the output transistors. The basic test is collector-emitter resistance. Transistors should measure open circuit from collector to emitter. So set your multimeter to the highest resistance range (probably 20 MΩ) (or if it's an auto-ranging meter, just set it to the resistance range) and connect the probes between the collector (case) and emitter of a transistor. Try the multimeter both ways round. If the multimeter reading changes from "0L" (or whatever the multimeter shows on resistance range when the probes aren't connected to anything), the transistor is probably faulty. Although a very high resistance may be acceptable for a power transistor.
Don't touch both multimeter probes while you're making this measurement, otherwise the multimeter will measure the resistance of your body. This isn't dangerous at all, but it will affect the measurement. You can touch ONE probe - the one you're holding to the transistor's metal can - but only hold the plastic part of the other probe.
Here is the pinout for this package, which is called a TO-3.
Let me know the results, and also the make and model of your multimeter.
Also, keep track of whether there are any plastic or mica insulating pieces used with the transistors or the bolts that hold them. You will need to get new ones, and fit them the same as the old ones were fitted. Also keep track of where the white heatsink compound was previously spread.
OK, do you have a multimeter? What make and model?
You can start by measuring the output transistors. The basic test is collector-emitter resistance. Transistors should measure open circuit from collector to emitter. So set your multimeter to the highest resistance range (probably 20 MΩ) (or if it's an auto-ranging meter, just set it to the resistance range) and connect the probes between the collector (case) and emitter of a transistor. Try the multimeter both ways round. If the multimeter reading changes from "0L" (or whatever the multimeter shows on resistance range when the probes aren't connected to anything), the transistor is probably faulty. Although a very high resistance may be acceptable for a power transistor.
Don't touch both multimeter probes while you're making this measurement, otherwise the multimeter will measure the resistance of your body. This isn't dangerous at all, but it will affect the measurement. You can touch ONE probe - the one you're holding to the transistor's metal can - but only hold the plastic part of the other probe.
Here is the pinout for this package, which is called a TO-3.
Let me know the results, and also the make and model of your multimeter.
Also, keep track of whether there are any plastic or mica insulating pieces used with the transistors or the bolts that hold them. You will need to get new ones, and fit them the same as the old ones were fitted. Also keep track of where the white heatsink compound was previously spread.
Ok tested the first transistor with the meter set to 20k and results are
Black probe on point B
Red probe on point E
Reading is 5.84
Red probe on point C
Black probe on point B
Reading 5.55
No reading from any other combinations
This is the multi meter it am using
Just bought it from napkin electronics yesterday
N19BW digital multi meter
Black probe on point B
Red probe on point E
Reading is 5.84
Red probe on point C
Black probe on point B
Reading 5.55
No reading from any other combinations
This is the multi meter it am using
Just bought it from napkin electronics yesterday
Being stupid you already said collector and emitter
KrisBlueNZ
Sadly passed away in 2015
The diode range is marked with the red circle, but I'm interested in measuring leakage. Your results in post #24 are good, but it's better if you use the 2000k range, marked with the green circle. Use the black lead in the COM socket and the red lead in the VΩmA socket, as normal.
The meter should read 0L (or something like that). Touch the probes together. It should read 0000 or some low number. If that's OK, you're set.
The MJ15003s are NPNs. For them, put the red probe on the collector (case) and the black probe to the base, and then to the emitter. The meter should continue to read 0L in both cases.
The MJ15004s are PNPs. For them, do the same but with the red and black probes reversed.
There's no need to measure any other combinations of pins.
KrisBlueNZ
Sadly passed away in 2015
That's right. The MJ15003s are NPNs and the MJ15004s are PNPs. There should be two of each. Each channel has one NPN and one PNP.
Second transistor NPN MJ15003 with the red probe on the collector
I get 0000 from base and emitter
Third transistor PNP MJ15004
Black probe on the collector
No reading from base
No reading from emitter
Transistor number 4 NPN MJ15003
Red probe on collector
No reading from base
No reading from emitter
Hope I am doing this right .
I get 0000 from base and emitter
Third transistor PNP MJ15004
Black probe on the collector
No reading from base
No reading from emitter
Transistor number 4 NPN MJ15003
Red probe on collector
No reading from base
No reading from emitter
Hope I am doing this right .
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If I had to replace the 504, would these be correct ?
http://www.digikey.co.uk/product-search/en?x=21&y=7&lang=en&site=uk&KeyWords=MJ15004
http://www.digikey.co.uk/product-search/en?x=21&y=7&lang=en&site=uk&KeyWords=MJ15004
KrisBlueNZ
Sadly passed away in 2015
When you say "no reading", do you mean that the meter shows 0L, just like it does when nothing is connected to the probes? If so, then those transistors are probably OK.
The second transistor, MJ15003, that reads 0000 to the emitter and to the base, is definitely dead.
When you tested the first MJ15004, in post #33, you say the number was around 1200 with some variation. Is it possible you were touching the red probe with your finger? So your body would have been connected to both probes? This will affect the reading. You can have your fingers in contact with one probe, but not both. Try the measurement again.
Next, can you upload some fairly close-up photos of the part of the circuit board close to the heatsinks. Take the photos from directly above the board, in natural light if possible, no flash, no direct sunlight. See https://www.electronicspoint.com/resources/how-to-take-photos-of-circuit-boards.6/
The second transistor, MJ15003, that reads 0000 to the emitter and to the base, is definitely dead.
When you tested the first MJ15004, in post #33, you say the number was around 1200 with some variation. Is it possible you were touching the red probe with your finger? So your body would have been connected to both probes? This will affect the reading. You can have your fingers in contact with one probe, but not both. Try the measurement again.
Next, can you upload some fairly close-up photos of the part of the circuit board close to the heatsinks. Take the photos from directly above the board, in natural light if possible, no flash, no direct sunlight. See https://www.electronicspoint.com/resources/how-to-take-photos-of-circuit-boards.6/
KrisBlueNZ
Sadly passed away in 2015
Hi again. Sorry for the delay.
Yes, those pictures are very good, thanks.
I'm asking a lot of questions in this post. Can you go through it point by point and respond to all of them please.
When you said in post #18 that you had accidentally connected positive and negative voltages backwards, what exactly did you do? And did you make the same mistake on both channels?
And the four fuses in a row that blew, that you replaced with the fusible resistor things, they're F1, F2, F3 and F4, right?
And one of the output transistors is short, but the other three are OK, right? The meter on the 2000 kΩ range shows "1" (same as when probes aren't touching anything) when you measure from collector to emitter?
Yes, the transistor you linked in post #35 is the MJ15004. I'm not sure whether to suggest that you replace all four of the output transistors, or just the faulty one. The other ones may have been stressed, and that multimeter test is good but doesn't guarantee that they're OK. They're not very expensive. How do you feel about replacing them all?
Can you please unclip the four metal clips that are holding the driver transistors onto the sides of the heatsinks, and tell me the markings on those transistors. There's an error in the schematic and I need to know the actual part numbers.
Yes, those pictures are very good, thanks.
I'm asking a lot of questions in this post. Can you go through it point by point and respond to all of them please.
When you said in post #18 that you had accidentally connected positive and negative voltages backwards, what exactly did you do? And did you make the same mistake on both channels?
And the four fuses in a row that blew, that you replaced with the fusible resistor things, they're F1, F2, F3 and F4, right?
And one of the output transistors is short, but the other three are OK, right? The meter on the 2000 kΩ range shows "1" (same as when probes aren't touching anything) when you measure from collector to emitter?
Yes, the transistor you linked in post #35 is the MJ15004. I'm not sure whether to suggest that you replace all four of the output transistors, or just the faulty one. The other ones may have been stressed, and that multimeter test is good but doesn't guarantee that they're OK. They're not very expensive. How do you feel about replacing them all?
Can you please unclip the four metal clips that are holding the driver transistors onto the sides of the heatsinks, and tell me the markings on those transistors. There's an error in the schematic and I need to know the actual part numbers.
this is what colour should have went where, i had them reversed by mistake !!
yes
yes
depending on cost, i dont mind replacing all four to be on the safe side
numbers on the smaller transisters under the clips is
D1763
F 952
and
B1186
E 939
soorry i dont know how to use the quote function lol, YET!
(KrisBlueNZ: I've fixed the quoting in this post. Click Edit to see how to do it.)
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