I'm hoping I finally found the right people to help me tackle this project. I am Currently building a Raspberry Pi/DigiAmp+/Volumio based system with touchscreen into an old Harmon Kardon CD101 tape deck. I replaced the Tape section with the touchscreen and the rest of the system is essentially gutted. The large input level knob has a new rotary encoder behind it for tactile hardware inputs rather than just touchscreen controls. I will utilize other buttons and encoders just to make use of and integrate as much of the face plate as possible. I am going as far as removing some labels and making decals that match the design when a function has been repurposed.
One function that was #1 on my list to repurpose was the level meter in the faceplate. This particular model has a little standalone circuit board running LCD display (Level Meter) The meter is connected to the little board via a small a harness and the little board is connected to the main deck through a ribbon cable. I didn't need to figure out wire usage from small board to LCD as both units were retained and plug into each other and only each other.
I had to figure out what the 6 wires (5 in a ribbon +1 standalone) were. I'm the type of person who will learn anything to achieve a goal but electronics give me a run for my money. Especially when it comes to reading diagrams and calculations and that kind of stuff.
I have figured out this boards 5 wires going in are +VCC which is 12.7, Then V-, Then Ground, Then 2 audio signals, and the standalone wire was the hardest to figure out but I believe its another +Vcc (The standalone wire is the one at the bottom of the LCD picture below traced in blue) Through metering different things and reading component numbers I figured out which wire is which in this 5 cable ribbon.
This image below is the two signal lines going into the board.
This last image is the blue standalone wire that goes to a few capacitors and such then the power supply.
I hooked it all up and it doesn't work.
My only idea is one thing I questioned all along.... I don't know what kind of audio signal this is running off of. Its internal in a tape deck from a bookshelf system so it is not amplified. It also appears to cut in with the headphone jacks so I figured it was some type of analog basic R+ and L+. For testing purposes I hooked it up to my amplified speaker positives but had the volume down almost to zero.
NOTHING! I am hoping you guys can look at these pictures from the service manual and help me figure out what kind of signal I need to get this meter working. I would like to stay with the original HK meters instead of something more modern just for aesthetic reasons.
I am at work right now and cannot test things but I did have the idea come across my mind today that when I did these tests I did NOT have speakers plugged in and that may be why the meters didn't work, with no load on the amplifier, no current coming through the wires? This troubleshooting shows my weakness in this project.
If you guys could give me any pointers to getting these control board the signal it needs that would be awesome.
One last point of information is, yes, I know the LCD's DO work. In some of my troubleshooting when I was plugging the LCD harness in it was on an angle so not all pins were making contact and the LCD would light up constant to full meter.
No magic smoke has been let out and all components looks to be in good operation condition, I'm confident with the right "Signal" this should work.
One function that was #1 on my list to repurpose was the level meter in the faceplate. This particular model has a little standalone circuit board running LCD display (Level Meter) The meter is connected to the little board via a small a harness and the little board is connected to the main deck through a ribbon cable. I didn't need to figure out wire usage from small board to LCD as both units were retained and plug into each other and only each other.
I had to figure out what the 6 wires (5 in a ribbon +1 standalone) were. I'm the type of person who will learn anything to achieve a goal but electronics give me a run for my money. Especially when it comes to reading diagrams and calculations and that kind of stuff.
I have figured out this boards 5 wires going in are +VCC which is 12.7, Then V-, Then Ground, Then 2 audio signals, and the standalone wire was the hardest to figure out but I believe its another +Vcc (The standalone wire is the one at the bottom of the LCD picture below traced in blue) Through metering different things and reading component numbers I figured out which wire is which in this 5 cable ribbon.
This image below is the two signal lines going into the board.
This last image is the blue standalone wire that goes to a few capacitors and such then the power supply.
I hooked it all up and it doesn't work.
My only idea is one thing I questioned all along.... I don't know what kind of audio signal this is running off of. Its internal in a tape deck from a bookshelf system so it is not amplified. It also appears to cut in with the headphone jacks so I figured it was some type of analog basic R+ and L+. For testing purposes I hooked it up to my amplified speaker positives but had the volume down almost to zero.
NOTHING! I am hoping you guys can look at these pictures from the service manual and help me figure out what kind of signal I need to get this meter working. I would like to stay with the original HK meters instead of something more modern just for aesthetic reasons.
I am at work right now and cannot test things but I did have the idea come across my mind today that when I did these tests I did NOT have speakers plugged in and that may be why the meters didn't work, with no load on the amplifier, no current coming through the wires? This troubleshooting shows my weakness in this project.
If you guys could give me any pointers to getting these control board the signal it needs that would be awesome.
One last point of information is, yes, I know the LCD's DO work. In some of my troubleshooting when I was plugging the LCD harness in it was on an angle so not all pins were making contact and the LCD would light up constant to full meter.
No magic smoke has been let out and all components looks to be in good operation condition, I'm confident with the right "Signal" this should work.
Here is a link to the service manual for the specific model if it helps any.
https://elektrotanya.com/the_harman_kardon_cd101.pdf/download.html#dl
https://elektrotanya.com/the_harman_kardon_cd101.pdf/download.html#dl
Hi Brian,
I like your project--- sounds like fun.
I'll describe how the circuit works, assuming it's working properly. The "PCB-3" is driven by two audio signals corresponding to the two channels being monitored. Signals would have an amplitude of a few volts peak-to-peak, roughly preamp line out levels as a guess. Q401 is a unity-gain buffer and drives a diode rectifier that converts the AC signal to DC (D401 and C405). The detected voltage is calibrated via VR401 and passes to the display sub-module; the larger the positive detected voltage the larger display amplitude. The other channel has duplicate circuitry. The signal in blue appears to be an enable control that that activates the display, i.e. an electronic power switch.
Your description mentions a LCD display, but the schematic claims a LED display. In any case, I imagine there's a display driver IC controlling the display elements. If there a type number visible, that might be insightful re sensitivity of control inputs.
I can provide more detail where needed. Can you elaborate what you'd like to do with the meter section?
Steve
I like your project--- sounds like fun.
I'll describe how the circuit works, assuming it's working properly. The "PCB-3" is driven by two audio signals corresponding to the two channels being monitored. Signals would have an amplitude of a few volts peak-to-peak, roughly preamp line out levels as a guess. Q401 is a unity-gain buffer and drives a diode rectifier that converts the AC signal to DC (D401 and C405). The detected voltage is calibrated via VR401 and passes to the display sub-module; the larger the positive detected voltage the larger display amplitude. The other channel has duplicate circuitry. The signal in blue appears to be an enable control that that activates the display, i.e. an electronic power switch.
Your description mentions a LCD display, but the schematic claims a LED display. In any case, I imagine there's a display driver IC controlling the display elements. If there a type number visible, that might be insightful re sensitivity of control inputs.
I can provide more detail where needed. Can you elaborate what you'd like to do with the meter section?
Steve