Hi all,
I try to repair this Kenwood L-A1 japanese version 100V/50Hz as it is very often not come out of protection from standby mode.
Hi all,
I try to repair this Kenwood L-A1- a japanese version 100V/50Hz as it is very often can not come out of protection from standby mode.
This amp uses a uCOM to control the whole amp and has also a inrush current limiter circuit with soft start relay etc.
I have tried to replaced all electrolytic caps excerpt two large PS cans but it just sometimes come out of protection if i press the amp on/off several times, most of the case the standby led flickers as long as after you press again the power on knob.
If it comes out of protection i can meassure dc offset just about 18mV from
Speaker both channels and can adjust the idle current 6mV as it describes in the service manual and it runs very good.
All voltages at protection IC 13/uPC1237HA are in manufacturers specs while it comes out of protection and runs well.
But next time in the same day you want to use it it again stays in protection like bollows:
If I press the power on button i hear the power relay clicks, then rush relay clicks, power led flickers, shortly further i hear the the speaker relays clicks or power/rush relays click off i do not know and so it further stays in protection as power led flickers until you must power it off.
For my seeking of reason and my repair purpose i have checked the standby board/circuit there is + 5,6V available for the uCOM as well as + 11 V for the power relay, -12V for the rush relay is also OK, relay driver transistors for power relay, rush relay are OK by DMM diode test.
No components look like burnt, or smoked .
Looking the service manual by protection portion i get 0V or mV at pin 1 of the protection IC uPC1237HA from NEC while the unit in standby or while the led flickers
Now i wants to get the voltage at pin 2 but before I will do it I find on my actual L-A1 kenwood obmits 2 resistors R178 and R179 each 390K ohm it does shows on the service manual so i wonder is it the reason for the protection mode of my amp?
Since I do not understand much from the protection circuit from NEC uPC1237HA so I do not know whether its is Ok with it order not.
Maybe someone of you can explain me that-Thank you in advance!
Here are the links for service manual downloads
KENWOOD LA-1, Service Manual, Repair Schematics
or
Kenwood | Hifi Manuals Free: page 12
I try to repair this Kenwood L-A1 japanese version 100V/50Hz as it is very often not come out of protection from standby mode.
Hi all,
I try to repair this Kenwood L-A1- a japanese version 100V/50Hz as it is very often can not come out of protection from standby mode.
This amp uses a uCOM to control the whole amp and has also a inrush current limiter circuit with soft start relay etc.
I have tried to replaced all electrolytic caps excerpt two large PS cans but it just sometimes come out of protection if i press the amp on/off several times, most of the case the standby led flickers as long as after you press again the power on knob.
If it comes out of protection i can meassure dc offset just about 18mV from
Speaker both channels and can adjust the idle current 6mV as it describes in the service manual and it runs very good.
All voltages at protection IC 13/uPC1237HA are in manufacturers specs while it comes out of protection and runs well.
But next time in the same day you want to use it it again stays in protection like bollows:
If I press the power on button i hear the power relay clicks, then rush relay clicks, power led flickers, shortly further i hear the the speaker relays clicks or power/rush relays click off i do not know and so it further stays in protection as power led flickers until you must power it off.
For my seeking of reason and my repair purpose i have checked the standby board/circuit there is + 5,6V available for the uCOM as well as + 11 V for the power relay, -12V for the rush relay is also OK, relay driver transistors for power relay, rush relay are OK by DMM diode test.
No components look like burnt, or smoked .
Looking the service manual by protection portion i get 0V or mV at pin 1 of the protection IC uPC1237HA from NEC while the unit in standby or while the led flickers
Now i wants to get the voltage at pin 2 but before I will do it I find on my actual L-A1 kenwood obmits 2 resistors R178 and R179 each 390K ohm it does shows on the service manual so i wonder is it the reason for the protection mode of my amp?
Since I do not understand much from the protection circuit from NEC uPC1237HA so I do not know whether its is Ok with it order not.
Maybe someone of you can explain me that-Thank you in advance!
Here are the links for service manual downloads
KENWOOD LA-1, Service Manual, Repair Schematics
or
Kenwood | Hifi Manuals Free: page 12
Attachments
The question is over current or over voltage on the output stage.
Check the DC voltage on the output emitters, ensure it is 0volts. I suspect it will not be.
This amplifier is from 1993 and will probably need replacement of the coupling capacitors first. You may be lucky and pin point the leaky one or two.
Check the DC voltage on the output emitters, ensure it is 0volts. I suspect it will not be.
This amplifier is from 1993 and will probably need replacement of the coupling capacitors first. You may be lucky and pin point the leaky one or two.