Hello all,
I have an integrated ampfiler Technics SU-A700 Mk2 . It has been working well for many years but now when connected to mains it remains in stand-by and does not want to power up. Sometimes it turns on normaly and works normaly but it looks to be absolutely randomly. I did not observe any systematic behavior in this. There is the same behavior when trying to turn it on with POWER button on a panel or using remote control. Also the same with connected inputs and speakers and disconnected.
I have done a very basic diagnostic. I have checked if the speakers are not shorted - they were not, I have opened the cover hoping I'll see something evident but I haven's seen any burned parts or blown-out capacitors. I have tried to measure the voltages on the power supply's output but not aware if they are correct (34 V, 34 V, 6.5 V, 6.3 V all AC against ground). I have also checked the switch with a beeper.
So before I start a complex diagnostics and do crazy things I would like to ask here if ti's not an "old pain" of these units being so long in service or if someone had the same issue and has already resolve it. I have downloaded a service manual which shows mainly how to operate and disassemble the unit and schematics and PCBs layouts.
Thanks all in advace.
Regards
Kamil
I have an integrated ampfiler Technics SU-A700 Mk2 . It has been working well for many years but now when connected to mains it remains in stand-by and does not want to power up. Sometimes it turns on normaly and works normaly but it looks to be absolutely randomly. I did not observe any systematic behavior in this. There is the same behavior when trying to turn it on with POWER button on a panel or using remote control. Also the same with connected inputs and speakers and disconnected.
I have done a very basic diagnostic. I have checked if the speakers are not shorted - they were not, I have opened the cover hoping I'll see something evident but I haven's seen any burned parts or blown-out capacitors. I have tried to measure the voltages on the power supply's output but not aware if they are correct (34 V, 34 V, 6.5 V, 6.3 V all AC against ground). I have also checked the switch with a beeper.
So before I start a complex diagnostics and do crazy things I would like to ask here if ti's not an "old pain" of these units being so long in service or if someone had the same issue and has already resolve it. I have downloaded a service manual which shows mainly how to operate and disassemble the unit and schematics and PCBs layouts.
Thanks all in advace.
Regards
Kamil
Suspect dried capacitor all small caps must g😵r dry solder joint. Inspect and resolder all joints under board and after that check how it's going the amp prior to replace caps.
Q814 is a relay drive; its base is driven by IC801 pin 26.
Also, IC801 pin 18 (the reset pin, normally low) has two states:
1. Floating 5V
2. Low, when the Q815 is conducting
... you should check that as well... IC802 controls the reset function
Good luck.
Also, IC801 pin 18 (the reset pin, normally low) has two states:
1. Floating 5V
2. Low, when the Q815 is conducting
... you should check that as well... IC802 controls the reset function
Good luck.
Thank you Extreme_Boky.
According to your advice it looks like something holds the unit in reset.
On IC801 pin 18 has 4.7 V and pin 26 has 2.4 V. Q814's and Q815's bases have about 2.5 V.
Please do you have any idea where to get a datasheet of M37470M2232S (IC801)? I tried to google but everytime I get it's not available for my country.
Thanks.
According to your advice it looks like something holds the unit in reset.
On IC801 pin 18 has 4.7 V and pin 26 has 2.4 V. Q814's and Q815's bases have about 2.5 V.
Please do you have any idea where to get a datasheet of M37470M2232S (IC801)? I tried to google but everytime I get it's not available for my country.
Thanks.
I'd do basic checks first, like voltages (bulging capacitors, overheated spots on the PCB where the voltage regs are, cold solder joints). Check the X801 (most likely a ceramic rezonator) clock signal... and in general -> make sure all switch contacts are clean, all PCB ground connectivity is sound. Make sure the case panels are properly interconnected (rust/oxidation) to keep the whole case potential at ground. Here's the schematics. The ICs are most likely okay.
IC802 properly initialises the IC801 after the power-up from cold.. see here:
IC802 properly initialises the IC801 after the power-up from cold.. see here:
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2.5 V on the base of Q815?! You have a bad (leaky) C806 if nothing else. That might be even the entire problem. This cap needs to do its job properly for power-on reset to work. ("Bad electrolytic in the reset circuit" is an absolute classic fault.)