hallo.
with the search button you will find some threads for mf b1.........
e.g.
Index of /pdf/Service Manuals/Musical Fidelity
and so on.........
einfach search am ende der seite unten benützen
grüsse
with the search button you will find some threads for mf b1.........
e.g.
Index of /pdf/Service Manuals/Musical Fidelity
and so on.........
einfach search am ende der seite unten benützen
grüsse
B1 Hot resistor
Hi,
I just "achieved" the same condition during tuning by creating a short circuit. Are all 8 transistors getting hot or only one line(4pcs) ? (of course aside of hot resistor) I think in my case I have to exchange all 8 transistors after 20 years of operation.
Have a nice weekend.
Goetz
Hi,
I just "achieved" the same condition during tuning by creating a short circuit. Are all 8 transistors getting hot or only one line(4pcs) ? (of course aside of hot resistor) I think in my case I have to exchange all 8 transistors after 20 years of operation.
Have a nice weekend.
Goetz
Hi,
I just "achieved" the same condition during tuning by creating a short circuit. Are all 8 transistors getting hot or only one line(4pcs) ? (of course aside of hot resistor) I think in my case I have to exchange all 8 transistors after 20 years of operation.
Have a nice weekend.
Goetz
I have to switch off the power before the transistors have time to get hot but I'm thinking of changing the transistors, just don't want the problem to be still there if I do
Output transistor failure is indeed the main problem with these amps. The 2n3055's fitted (Pecor if I remember correctly) are a cheap and nasty type and you would do well to replace them with better quality devices
They are pecor I have easy access to some ST (ON?) types seem cheap tho! and would a blown transistor cause that resistor to over heat? thanks
Yes it would indeed cause r68 to smoke...
ST and ON Semi are different companies. ON used to be Motorola.
Any reputable brand should be ok but watch for fakes and try and get all 8 from the same batch. Best go to the likes of R.S, Farnell, Digikey etc to ensure the above criterion.....
If you can get non fake ST micro made in morocco they usually live up to their datasheets specs. I've tortured a lot of different ST power transistors and they have all held out really well. Even their plastic case tip35c's I've ran at nearly twice their dissipation limit for hours at a time and I believe I still have a few of them in working order.
any ideas?R68 smoking up could only be caused by a short across the + side of the psu to ground. The output devices having failed is by far the most likely problem but if you have replaced all of these, and you are sure the new parts are all OK, check C31 (smoothing cap 4700uF). If this has failed short it would cause the fault you describe.
More likely..... a fault further up stream that's causing T20, T22 to turn hard on. In which case R64,66 (0R47) will be getting hot also but probably not hot enough to smoke after just a second or two.
Check T18 (BD140) and R58 (100R 1W) as likely culprits.
If the original fault was still present after you switched the amp on with the new 3055s then it is of course possible that you have blown outputs once again.....
A check with a multimeter on the outputs should sort that out.
More likely..... a fault further up stream that's causing T20, T22 to turn hard on. In which case R64,66 (0R47) will be getting hot also but probably not hot enough to smoke after just a second or two.
Check T18 (BD140) and R58 (100R 1W) as likely culprits.
If the original fault was still present after you switched the amp on with the new 3055s then it is of course possible that you have blown outputs once again.....
A check with a multimeter on the outputs should sort that out.
R68 smoking up could only be caused by a short across the + side of the psu to ground. The output devices having failed is by far the most likely problem but if you have replaced all of these, and you are sure the new parts are all OK, check C31 (smoothing cap 4700uF). If this has failed short it would cause the fault you describe.
More likely..... a fault further up stream that's causing T20, T22 to turn hard on. In which case R64,66 (0R47) will be getting hot also but probably not hot enough to smoke after just a second or two.
Check T18 (BD140) and R58 (100R 1W) as likely culprits.
If the original fault was still present after you switched the amp on with the new 3055s then it is of course possible that you have blown outputs once again.....
A check with a multimeter on the outputs should sort that out.
I noticed R69 also getting hot but no smoke
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