Yes, thanks, I've done a complete recap, apart from the massive beer can reservoirs. Sounds amazing now! I got quite a few hours out of it before the zener/regulator failed again.
This issue with the regulator seems to be a known problem to this amp.
http://www.audiotecnico.it/riparazi...s/immagini/Krell_KSA50s_regolatore_driver.JPG
Call Krell service department, I`m sure they will give you guidance...
http://www.audiotecnico.it/riparazi...s/immagini/Krell_KSA50s_regolatore_driver.JPG
Call Krell service department, I`m sure they will give you guidance...
Label them to 4
Amp1
Burnt: 484024 x2, 0.5ohm E resistor had some mark
Pre-drive E resistor was 1ohm + 5.6ohm (others was 1ohm + 3.3ohm)
Amp2
Burnt: 10ohm, but don't know that was for +-45V' power or pre-drive transistor B.
Both channel had the D3, D12 burnt mark on board, but measured Diodes are good.
Amp3
Burnt: 484002 x1
Amp4
Burnt: 484002 x1 and related 0.5ohm, 3.3ohm, one 0.5ohm was broken.
-----------------
All pre-drive transistors are measured in good condition.
investigated so far
-----------------
Will do:
Re-caps all
Replace for:
all +-45V' 10 ohm power resistors from 2W to 7W
all +-18v zener 1N4740 & 1N4743 to 1N5349 (11.4V 5w), (get idea from earlier post of your guys)
all pre-drive B resistor 10ohm
all pre-drive E resistors 1ohm + 3.3 ohm
all power drive E resistor 0.5ohm to Dale or CadDock, because the time tells, RCD isn't that good.
-----------
Hope some one can give me any advise, please
-----------
Those amps are mine, they work for my active crossover, and separate speakers and speaker drivers for stereo channel etc...
Amp1
Burnt: 484024 x2, 0.5ohm E resistor had some mark
Pre-drive E resistor was 1ohm + 5.6ohm (others was 1ohm + 3.3ohm)
Amp2
Burnt: 10ohm, but don't know that was for +-45V' power or pre-drive transistor B.
Both channel had the D3, D12 burnt mark on board, but measured Diodes are good.
Amp3
Burnt: 484002 x1
Amp4
Burnt: 484002 x1 and related 0.5ohm, 3.3ohm, one 0.5ohm was broken.
-----------------
All pre-drive transistors are measured in good condition.
investigated so far
-----------------
Will do:
Re-caps all
Replace for:
all +-45V' 10 ohm power resistors from 2W to 7W
all +-18v zener 1N4740 & 1N4743 to 1N5349 (11.4V 5w), (get idea from earlier post of your guys)
all pre-drive B resistor 10ohm
all pre-drive E resistors 1ohm + 3.3 ohm
all power drive E resistor 0.5ohm to Dale or CadDock, because the time tells, RCD isn't that good.
-----------
Hope some one can give me any advise, please
-----------
Those amps are mine, they work for my active crossover, and separate speakers and speaker drivers for stereo channel etc...
It looks like no one interesting for my request.
Never mind, this amp is too old for everyone I believe.
All four amps have modified, re-caped and restored now, all work good.
The way to fix below:
They've had this common issue as all KSA-50S:
1. Two Zenners was not enough to drop the voltage down to lower than 35v, and they were running too hot then get break thru.
2. Then, the titan cap will be blowed, two of the amps had this issue.
3. Then, the regulator will be blowed, one of the amps has changed regulator before me.
Solution:
1. Change Zener to three 1N5340BG (10v, 5w), drop the voltage to 30v.
2. Change C6, C8 to 33UF/63v, that never blow up again even Zener over heat and get break thru.
3. Change regulators to NJM7818FA & NJM7918FA, they are 1.5A, higher than normal one 1A, and they have over voltage protection, tested, connect to 60v, output is 0v.
4. Change C7, C9 to 100UF/25v, stop the surge as much as it can. (may not need, but I like to do this)
5. The T-Cap in drive board, those don't need to change, unless died, my case one of the amps was.
6. Soldering:
All Zeners and regulators, soldered to the opposite side of PCB as before,
Zenners raise up 1.5mm from PCB.
Added a 3mm thick silicon conduct pad, between the Zeners, regulators and heat sink, let the heat sink spread the heat.
And that is all, hope they never get problem again.
All amps are working now, all drive board did not have problem, they are all good and reliable.
They are good amp accepted this common issue.
The pictures and procedures, posted to
review33.com - 影音天地
Never mind, this amp is too old for everyone I believe.
All four amps have modified, re-caped and restored now, all work good.
The way to fix below:
They've had this common issue as all KSA-50S:
1. Two Zenners was not enough to drop the voltage down to lower than 35v, and they were running too hot then get break thru.
2. Then, the titan cap will be blowed, two of the amps had this issue.
3. Then, the regulator will be blowed, one of the amps has changed regulator before me.
Solution:
1. Change Zener to three 1N5340BG (10v, 5w), drop the voltage to 30v.
2. Change C6, C8 to 33UF/63v, that never blow up again even Zener over heat and get break thru.
3. Change regulators to NJM7818FA & NJM7918FA, they are 1.5A, higher than normal one 1A, and they have over voltage protection, tested, connect to 60v, output is 0v.
4. Change C7, C9 to 100UF/25v, stop the surge as much as it can. (may not need, but I like to do this)
5. The T-Cap in drive board, those don't need to change, unless died, my case one of the amps was.
6. Soldering:
All Zeners and regulators, soldered to the opposite side of PCB as before,
Zenners raise up 1.5mm from PCB.
Added a 3mm thick silicon conduct pad, between the Zeners, regulators and heat sink, let the heat sink spread the heat.
And that is all, hope they never get problem again.
All amps are working now, all drive board did not have problem, they are all good and reliable.
They are good amp accepted this common issue.
The pictures and procedures, posted to
review33.com - 影音天地