Evening,
Hoping someone on this forum has some experience with Music Hall a15.3. Bought it non-working, knowing it had one channel blown. But after removing and replacing the outputs (I replaced original 2SA1186/2SC2837 with 2SA1386/2SC3519 - which seemed like an exact match but with higher voltage and amperage ratings, albeit slightly slower at 30MHz vs 60MHz). I also tested all other transistors with the DMM and they checked out good. Compared resistors, capacitors and diodes to each channel and those also checked out good.
Symptom(s) ---
Powering on the unit you can hear the two relays "click" but about 5 seconds later, you hear a third relay "click" on the input section and the front panel LEDs start blinking (tried to show in pictures below)
1) first pic is on power-up, volume control and selected input LEDs light up
2) after about 5 seconds from relays clicking in, all the front panel LEDs light up
3) all the front panel LEDs continue to flash every second until you turn the power off (powering up again, starts this process over again)
I cannot find anything wrong with either power amplifier section - both have about 15mV of bias, pre-drivers get warm (maybe 90-degree F) but nothing too hot to touch comfortably. I also get 12mV and 9mV DC on the outputs - so it doesn't appear to be amplifier related due to protection kicking in.
I get all the low voltages as listed on the board +/-45V, +/-15V, +5V and +9V. Gone through the entire board checking resistors, diodes and capacitors and I have not found anything out of spec. (anything suspect, has been removed and tested out of circuit - with all testing good and soldered back in)
Anything you could suggest I try, or might know as a problem on these integrated amplifiers? I have had this sitting around for 2-3 months, working on it off and on - generally getting frustrated because I can't seem to find a faulty part.
Could it be one of the input "chips" or maybe the front panel "chip"? Not the best at reading a datasheet and circuit design and knowing how to confirm if it's working. I did check all the resistors and capacitors on the front panel and they seem in good working order and all measurements seem logical.
Could not find a schematic, so if someone has one would appreciate you sharing it with me.
Hoping someone on this forum has some experience with Music Hall a15.3. Bought it non-working, knowing it had one channel blown. But after removing and replacing the outputs (I replaced original 2SA1186/2SC2837 with 2SA1386/2SC3519 - which seemed like an exact match but with higher voltage and amperage ratings, albeit slightly slower at 30MHz vs 60MHz). I also tested all other transistors with the DMM and they checked out good. Compared resistors, capacitors and diodes to each channel and those also checked out good.
Symptom(s) ---
Powering on the unit you can hear the two relays "click" but about 5 seconds later, you hear a third relay "click" on the input section and the front panel LEDs start blinking (tried to show in pictures below)
1) first pic is on power-up, volume control and selected input LEDs light up
2) after about 5 seconds from relays clicking in, all the front panel LEDs light up
3) all the front panel LEDs continue to flash every second until you turn the power off (powering up again, starts this process over again)
I cannot find anything wrong with either power amplifier section - both have about 15mV of bias, pre-drivers get warm (maybe 90-degree F) but nothing too hot to touch comfortably. I also get 12mV and 9mV DC on the outputs - so it doesn't appear to be amplifier related due to protection kicking in.
I get all the low voltages as listed on the board +/-45V, +/-15V, +5V and +9V. Gone through the entire board checking resistors, diodes and capacitors and I have not found anything out of spec. (anything suspect, has been removed and tested out of circuit - with all testing good and soldered back in)
Anything you could suggest I try, or might know as a problem on these integrated amplifiers? I have had this sitting around for 2-3 months, working on it off and on - generally getting frustrated because I can't seem to find a faulty part.
Could it be one of the input "chips" or maybe the front panel "chip"? Not the best at reading a datasheet and circuit design and knowing how to confirm if it's working. I did check all the resistors and capacitors on the front panel and they seem in good working order and all measurements seem logical.
Could not find a schematic, so if someone has one would appreciate you sharing it with me.
Attachments
Thought I'd bring this back up to see if anyone has a clue of what I can try? Should I try replacing the IC (STC12C5A32AD) on the front panel? I'm at a loss but willing to try anything - start throwing out ideas I can try.
Back Again - possibly wishful thinking, but I've made some ground, still need some assistance.
I replaced (3) NPNs (STS8050) and (1) PNP (STS8550) in the output relay section and 10V output switching ICs circuit. 1 PNP and 1NPN tested way different than the others, so I went ahead and replaced them all to be safe. Also replaced the surface mount caps on the front panel board and checked all resistors and fuses (everything checks out as good)
- that fixed the relay tripping and no music
still have the issue that after about 10 seconds from power-up, the front panel LEDs starting flashing (all of them) and I can no longer change the volume or the input, the remote will work for that initial 10-seconds but not the panel buttons or volume knob. After the 10-secs when the LEDs start flashing the remote no longer controls anything (front panel buttons/knobs never work)
What appears to be the issue is something on the front panel
- there is a STC chip (40-pin) thru-hole 12C5A32AD --- it gets warm and I ordered 2 replacements from AliExpress (neither work, amp won't even come on with either of them installed, highly likely they are fakes)
- there is a 16-pin SMD IC chip 74HC595D (8-bit shift register/Latch (3-state)) according to the datasheet. Took voltage measurements, but not sure what I'm looking for to confirm it works. It has the correct 5.0 Vdc on pin-16 (VCC) and GND on pin-8
Any ideas which one of these might be the IC causing my issue? the SMD 74HC595D is available at Mouser, but can't find the STC chip except in SMD square package and I haven't found a conversion board to go from 40-pin TH to SMD yet, if it would even fit, because the chip site at the top of the front panel, so a taller chip wouldn't allow the cover to go on.
Any insights would be appreciated.
I replaced (3) NPNs (STS8050) and (1) PNP (STS8550) in the output relay section and 10V output switching ICs circuit. 1 PNP and 1NPN tested way different than the others, so I went ahead and replaced them all to be safe. Also replaced the surface mount caps on the front panel board and checked all resistors and fuses (everything checks out as good)
- that fixed the relay tripping and no music
still have the issue that after about 10 seconds from power-up, the front panel LEDs starting flashing (all of them) and I can no longer change the volume or the input, the remote will work for that initial 10-seconds but not the panel buttons or volume knob. After the 10-secs when the LEDs start flashing the remote no longer controls anything (front panel buttons/knobs never work)
What appears to be the issue is something on the front panel
- there is a STC chip (40-pin) thru-hole 12C5A32AD --- it gets warm and I ordered 2 replacements from AliExpress (neither work, amp won't even come on with either of them installed, highly likely they are fakes)
- there is a 16-pin SMD IC chip 74HC595D (8-bit shift register/Latch (3-state)) according to the datasheet. Took voltage measurements, but not sure what I'm looking for to confirm it works. It has the correct 5.0 Vdc on pin-16 (VCC) and GND on pin-8
Any ideas which one of these might be the IC causing my issue? the SMD 74HC595D is available at Mouser, but can't find the STC chip except in SMD square package and I haven't found a conversion board to go from 40-pin TH to SMD yet, if it would even fit, because the chip site at the top of the front panel, so a taller chip wouldn't allow the cover to go on.
Any insights would be appreciated.
Attachments
Possibly available thru LCSC, which I have found to be generally reputable:
https://www.lcsc.com/products/Microcontrollers-MCU-MPU-SOC_11329.html?keyword=12C5A32AD PDIP40
Does this uC need to be flashed to operate?
https://www.lcsc.com/products/Microcontrollers-MCU-MPU-SOC_11329.html?keyword=12C5A32AD PDIP40
Does this uC need to be flashed to operate?
Thanks for the link, when I searched a few weeks back, I only found the SMD version.
I not 100% sure about the programming and if it's required, the circuit sems like a basic comparator H/L voltage, but you could be right, which means it's not going to be very useful if I have to look at blinking lights to listen to music.
I not 100% sure about the programming and if it's required, the circuit sems like a basic comparator H/L voltage, but you could be right, which means it's not going to be very useful if I have to look at blinking lights to listen to music.
That sucks if it is the uPC , it most likely needs a bootloader for whatever coding that it uses.
Then you would have to flash "music hall's" code.
I going to build a preamp with remote volume input switching , I want some standard arduino based
firmware on a hobby standard uPC.
Then you would have to flash "music hall's" code.
I going to build a preamp with remote volume input switching , I want some standard arduino based
firmware on a hobby standard uPC.