Hi, I'm repairing / restoring an old Yamaha multi CD player, model CDC-745. One of the faults is that it doesn't respond to the IR remote control. Using an Arduino-based IR sniffer, I've determined that the remote is sending valid NEC protocol codes, and therefore the problem is in the player rather than the remote. The player's schematic shows the IR sensor as 'U401', a 3-pin package (VO, VC and G). Physically, it's a small metal-encased unit with a photo diode on one side and three pins on the other.
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VC and VO both measure approx 4.9V, as per the schematic. VC goes to the 5V supply, G goes to ground, and VO goes directly to pin 14 on the player's main control IC. However, pressing a remote key doesn't trigger any pulses in VO or VC, so it appears that this sensor is dead. Plugging it into my Arduino sniffer also shows no change in VO or VC when a remote key is pressed; neither does the 'scope show any output.
I'd hoped this would be a simple swap-out for a standard 38KHz IR sensor such as TSOP4838, VS1838 or similar (which is what I use in the IR sniffer). But on removing U401 and undoing its metal case, I found a small circuit board with a photo-diode, an 8-pin IC marked on two lines '2800' and '427', two smd capacitors and an smd resistor. A DMM and 'scope test show that the photo diode seems to be OK (i.e. the DMM reads a forward voltage drop, and the 'scope shows some pulses when a remote key is pressed), so I'm assuming it's the IC that has failed.
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I tried installing a VS1838 anyway, just to see if it would work. The 'scope shows the expected pulses at VO and at pin 14 of the control IC when a remote key is pressed; unfortunately the player doesn't actually respond to the signal, so I assume that the IC in U401 translates to a different protocol or timing.
The service manual parts list shows U401 as part number "VK498900 - LT. DETECT" but Google hasn't been any help in tracking this down any further, other than identifying it as "YAMAHA VK498900 LIGHT DETECT MODULE". I've traced the schematic of U401 as per the image below, but I don't know what the IC is or what it does, nor do I know the value of the smd capacitors.
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So I'm a bit stuck and would appreciate any help or ideas as to where to go from here.