Help with Yamaha CD-745 CD Player IR sensor - Page 1
Forum section: electronics / repair

author: serafis
author_rank: Contributor
timestamp: November 10, 2021, 01:27:09 am
content: 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.[ Specified attachment is not available ] [ Specified attachment is not available ]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.[ Specified attachment is not available ] [ Specified attachment is not available ]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.[ Specified attachment is not available ]So I'm a bit stuck and would appreciate any help or ideas as to where to go from here.

author: serafis
author_rank: Contributor
timestamp: November 10, 2021, 03:08:40 am
content: On further investigation, I think the IC is possibly a NEC PC2800A Preamplifier for Infrared Remote Control (https://pdf1.alldatasheet.com/datasheet-pdf/view/6733/NEC/UPC2800.html) or similar.Still stuck though as I don't think I'll be able to find one of these in New Zealand.

author: andy3055
author_rank: Super Contributor
timestamp: November 10, 2021, 04:59:20 am
content: I once had a problem with an IR sensor in an Onkyo amp. It turns out that when the unit is on standby for long periods of time, it does damage the LED. I hardly used the amp and it was not switched on regularly. In my case, the LED was by itself with no other components on the small board it was mounted on. Luckily, it was available on eBay (I think). I wonder if you can get an IR LED and try it as chances are that the rest of it is still good.

author: serafis
author_rank: Contributor
timestamp: November 10, 2021, 06:07:02 am
content: Worth a try - I will look through the parts bin and see if I can find one. Thanks.

author: Renate
author_rank: Super Contributor
timestamp: November 10, 2021, 01:29:34 pm
content: Maybe try an inversion of the data out?It's not clear what polarity it would be expecting. I would think that the original circuit would demodulate but not alter the protocol (besides maybe polarity).

author: fzabkar
author_rank: Super Contributor
timestamp: November 10, 2021, 09:13:35 pm
content: Suggested diodes are "PH302, 302C, 310, 320, etc".https://www.renesas.com/us/en/document/dst/upc2800a-data-sheet

author: serafis
author_rank: Contributor
timestamp: November 15, 2021, 12:56:56 am
content: I replaced the photodiode, but no success. I'm waiting for a replacement chip to arrive and will try that - otherwise I think this'll just have to be a remoteless player.

author: Renate
author_rank: Super Contributor
timestamp: November 15, 2021, 02:58:10 am
content: I meant to try a bog standard 3 pin receiver and see if the ouput when inverted worked correctly. Did you try that?

author: andy3055
author_rank: Super Contributor
timestamp: November 15, 2021, 04:40:00 am
content: I came across this site:https://www.yoycart.com/Product/19489211497/Not sure if that is helpful at all!

author: serafis
author_rank: Contributor
timestamp: November 28, 2021, 11:35:31 pm
content: I replaced the IR preamp IC and the photodiode, and signals are now getting through to pin 14 of the main servo control IC when a remote key is pressed, but it still doesn't actually respond. So I think that's about as far as I'm going to go with this one. Thanks everyone for your help.