I have an old unbranded DAC from the early 90's (possibly DIY), where the SPDIF has stopped working. No signal lock. Optical however works perfect and DAC sounds great. I would like to get SPDIF going again. Any help would be appreciated.
The coax RCA jack (ground floating, not touching chassis) on the DAC is connected to the board via a 5" Belden RG179 75 Ohm cable. The center conductor goes directly to the primary of a 1:1 pulse transformer (Coilcraft WB1010). The shield is connected to the same transformer, but through a 10uF (electrolytic) and 0.1uF (ceramic in parallel) capacitors.
The secondary of the pulse transformer is connected/shunted by a 75 Ohm resistor. I measured the DCR of the primary and secondary windings with an Ohm meter and they were 0.4 Ohm, similar to the 0.3 Ohm listed in the datasheet.
I also replaced the 10uF electrolytic capacitor, as well as all electrolytic capacitors in the DAC with no change.
Passed the 75 Ohm resistor, the digital signal goes to pins 1 and 2 of a DS34C86N quad line receiver and then to a PC74HC86P Philips microchip.
I have this suspicion that possibly the quad line receiver has failed. But I'm not sure on how to test it. It's being fed by a present 5VDC. Is this something that's likely, or should I be looking elsewhere?
Any ideas, or suggestions are greatly appreciated. Also, if anyone has these chips as spares and is willing to sell them I would be interested in trying.
The coax RCA jack (ground floating, not touching chassis) on the DAC is connected to the board via a 5" Belden RG179 75 Ohm cable. The center conductor goes directly to the primary of a 1:1 pulse transformer (Coilcraft WB1010). The shield is connected to the same transformer, but through a 10uF (electrolytic) and 0.1uF (ceramic in parallel) capacitors.
The secondary of the pulse transformer is connected/shunted by a 75 Ohm resistor. I measured the DCR of the primary and secondary windings with an Ohm meter and they were 0.4 Ohm, similar to the 0.3 Ohm listed in the datasheet.
I also replaced the 10uF electrolytic capacitor, as well as all electrolytic capacitors in the DAC with no change.
Passed the 75 Ohm resistor, the digital signal goes to pins 1 and 2 of a DS34C86N quad line receiver and then to a PC74HC86P Philips microchip.
I have this suspicion that possibly the quad line receiver has failed. But I'm not sure on how to test it. It's being fed by a present 5VDC. Is this something that's likely, or should I be looking elsewhere?
Any ideas, or suggestions are greatly appreciated. Also, if anyone has these chips as spares and is willing to sell them I would be interested in trying.