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b500 problem
b500 problem
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Old 23rd May 2019, 10:12 PM   #1
karachay is offline karachay
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Default b500 problem

hi friends i try make b500 from apex. i get alot of problems this amp steal my 3weekends i know its easy but i dont know why i still get problems. i finally make it work. but after 2 3 times close and open, one resistor get flame and burnd. when i check it i see my 5200 transistors get short too and fuse blow.

the resistor is R21 on schematic. 100R.

any idea why it can happen? it was working really nice and not getting hot
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Old 24th May 2019, 12:20 PM   #2
karachay is offline karachay
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15032 and 15033 burned and 1943 transistors all is burned too.

i think i find the problem. it can be the small peace leave there when i open holes on heatsink and it drop on board and short the HV.

is there any thing else can be a reason?
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Old 26th May 2019, 06:37 AM   #3
karachay is offline karachay
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problem fixed. inside my 10 ne5532 only one of them was working but i think they are not good or fake so it get burn too. i put tl072 and all problems go away.

so if any one make b500 use tl072...
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Old 26th May 2019, 06:18 PM   #4
Ian Finch is offline Ian Finch  Australia
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Or buy genuine NE5532 from an authorized agency. Don't forget that there are bad copies of TL072 that are sold very cheap too. I know because I foolishly bought a bag full since they cost so little.
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Old 27th May 2019, 08:39 PM   #5
Mark Tillotson is offline Mark Tillotson
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Note the NE5532 and 34A need 100nF ceramic cap between +/- rails right at the chip, not inches away on the pcb. Not that this explains the fail mode.
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Old 28th May 2019, 12:20 AM   #6
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Mark Tillotson View Post
Note the NE5532 and 34A need 100nF ceramic cap between +/- rails right at the chip, not inches away on the pcb. Not that this explains the fail mode.
Unless the 5532 was oscillating.
Some of these high speed op amps can be a bit touchy.
1mm of pcb track = 1nH inductance.
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Old 28th May 2019, 01:56 AM   #7
karachay is offline karachay
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ty friends.

i get another problem again

positive side zener 2v. negative side is 15v. and at signal output have 67vdc any advice?

i change 4k7 5w resistor and the 10uf 100v capacitor but still same. now i am changing 100n my board turn to a trash cause of the repair
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Old 28th May 2019, 02:16 AM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by karachay View Post
ty friends.

i get another problem again

positive side zener 2v. negative side is 15v. and at signal output have 67vdc any advice?

i change 4k7 5w resistor and the 10uf 100v capacitor but still same. now i am changing 100n my board turn to a trash cause of the repair
Not much point changing random components.
You need to get your meter out and start measuring components for shorts.
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Old 28th May 2019, 02:35 AM   #9
karachay is offline karachay
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Quote:
Originally Posted by nigelwright7557 View Post
Not much point changing random components.
You need to get your meter out and start measuring components for shorts.
i did my friend its look like they are working and stop working and start again now i changing zener and i will test again.
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Old 28th May 2019, 02:39 AM   #10
nigelwright7557 is offline nigelwright7557  United Kingdom
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Originally Posted by karachay View Post
i did my friend its look like they are working and stop working and start again now i changing zener and i will test again.

If its intermittent first thing to do is do a good visual inspection for unsoldered or bad joints.
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