An acquaintance of a friend came to me and asked if I could look at this for him. He said he was using it, and then all of a sudden, both channels dropped out, he was using the digital coax in. I checked the optical input and it functions perfectly with both balanced and unbalanced output, there are three ICs that both the optical and coax feed into, a bit of switching circuitry. My gut tells me it’s one of these chips that has failed. I can’t find some of these at all and was hoping that maybe some of you could point me into a direction of a chip that would be sufficient. Sadly, I do not have a schematic so I can’t present its operation.
Here are the three chips that the two digital sources feed into.
The coax enters and goes through a coupling cap, the red Wima you see there and then goes into the SN75ALS195J.
There is this switch mounted to the front panel that has you switch between coax and optical
The switch goes to those two solder points I have circled in red. The one on the right is ground. So when you switch to optical what it does is it grounds out the trace that goes up between the ICs.
Since optical still functions perfectly it’s telling me it has to be one of these.
I went ahead and measured the voltages on all of the pins of the IC that the coax goes into.
Pin 1: ground
Pin 2: 1.9282 Vdc.
Pin to happens to be the input from the coax. The coax goes into the coupling and the coupling goes to pin two. Not sure if it supposed to be DC voltage there.
Pin 3: 3.6502 Vdc
Pin 4: 5.0946 vdc
Pin 5: 3.8087 vdc
Pin 6: 2.5982 vdc
Pin 7: 2.6592 vdc
Pin 8: ground
Pin 9: 2.2719 vdc
Pin 10: 2.5933 vdc
Pin 11: 3.8251 vdc
Pin 12: 0.0751 Vdc
Pin 13: 3.8299 vdc
Pin 14: 2.5883 vdc
Pin 15: 2.2645 vdc
Pin 16: 5.0947 Vdc
This is the pinout of that IC. This one is a bit over my head, having a hard time seeing what each pin is. Really wish I had a schematic.
It seems like my options are eBay, does anyone know of a chip that will replace this one? I see several SN75ALS194 or 193 for sale.
The other two ICs are available from Mouser or Digikey so no problem with those.
Do you think I am on the right track? Suggestions for that IC?
Thank you
Dan
Here are the three chips that the two digital sources feed into.
The coax enters and goes through a coupling cap, the red Wima you see there and then goes into the SN75ALS195J.
There is this switch mounted to the front panel that has you switch between coax and optical
The switch goes to those two solder points I have circled in red. The one on the right is ground. So when you switch to optical what it does is it grounds out the trace that goes up between the ICs.
Since optical still functions perfectly it’s telling me it has to be one of these.
I went ahead and measured the voltages on all of the pins of the IC that the coax goes into.
Pin 1: ground
Pin 2: 1.9282 Vdc.
Pin to happens to be the input from the coax. The coax goes into the coupling and the coupling goes to pin two. Not sure if it supposed to be DC voltage there.
Pin 3: 3.6502 Vdc
Pin 4: 5.0946 vdc
Pin 5: 3.8087 vdc
Pin 6: 2.5982 vdc
Pin 7: 2.6592 vdc
Pin 8: ground
Pin 9: 2.2719 vdc
Pin 10: 2.5933 vdc
Pin 11: 3.8251 vdc
Pin 12: 0.0751 Vdc
Pin 13: 3.8299 vdc
Pin 14: 2.5883 vdc
Pin 15: 2.2645 vdc
Pin 16: 5.0947 Vdc
This is the pinout of that IC. This one is a bit over my head, having a hard time seeing what each pin is. Really wish I had a schematic.
It seems like my options are eBay, does anyone know of a chip that will replace this one? I see several SN75ALS194 or 193 for sale.
The other two ICs are available from Mouser or Digikey so no problem with those.
Do you think I am on the right track? Suggestions for that IC?
Thank you
Dan
You are on the right track... by the way, that IC was already replaced previously. Or, you may have touched the solder joints with an iron..??
For a genuine part, try here... contact them to see if the part will indeed be available... Oct2024
https://au.mouser.com/ProductDetail/Texas-Instruments/SN75ALS195N?qs=8yeEWhuAOtPy%2B6AzryLKmg==
From what I see from the PCB underside, they paralleled the two differential buffers, to gain a better drive capability...
For a genuine part, try here... contact them to see if the part will indeed be available... Oct2024
https://au.mouser.com/ProductDetail/Texas-Instruments/SN75ALS195N?qs=8yeEWhuAOtPy%2B6AzryLKmg==
From what I see from the PCB underside, they paralleled the two differential buffers, to gain a better drive capability...
You are on the right track... by the way, that IC was already replaced previously. Or, you may have touched the solder joints with an iron..??
For a genuine part, try here... contact them to see if the part will indeed be available... Oct2024
https://au.mouser.com/ProductDetail/Texas-Instruments/SN75ALS195N?qs=8yeEWhuAOtPy%2B6AzryLKmg==
From what I see from the PCB underside, they paralleled the two differential buffers, to gain a better drive
I don’t know what happened above, but I appreciate your response. Yes I did actually remove the chip, but just put it back in as I had no way of really measuring and getting any useful data from it. I actually retouched all of the joints in the area just in case, but that IC is the only one to have the old solder removed and get new solder. I did see that Mouser was going to be getting some next fall, which was why I was curious if there was any other devices that would be able to fill-in and be equal or better.
What do you think of Arrow Electronics? I have ordered from them a few times and surprisingly loved their next day shipping, but as for authentic parts, are they good? I wouldn’t suspect them buying counterfeits, but just curious.
It shows that they have 66 in stock, and they are cheaper than both Mouser and Digikey.
If you all think that, yeah, you’re gonna be getting an authentic part then I will buy them tonight.
Dan
What do you think of Arrow Electronics? I have ordered from them a few times and surprisingly loved their next day shipping, but as for authentic parts, are they good? I wouldn’t suspect them buying counterfeits, but just curious.
It shows that they have 66 in stock, and they are cheaper than both Mouser and Digikey.
If you all think that, yeah, you’re gonna be getting an authentic part then I will buy them tonight.
Dan
I suppose you could try that part... The ICs are line receivers, differential line drivers/buffers - with enable... so I do not see any reason to make fakes... plus, they are obsolete and a very low demand part (no demand... apart from you needing one)
I'd install a DIL16 socket.. easy to try different ICs... sourced from different vendors... if you go down that path.
I'd install a DIL16 socket.. easy to try different ICs... sourced from different vendors... if you go down that path.
It looks to me like they enabled all four line receivers, but use only line receiver 1.
By the way, an inelegant solution might be to connect the AC coupled coaxial input to one of the other three line receivers. It will require some PCB trace cutting.
Pretty much dead on, 74.55 ohms. Yeah, I thought that should be as close to zero volts as possible.
Dan
I figured as much they being not a high demand part. I definitely plan on placing sockets into any place I remove a chip.
Dan
Moved to digital line level per forum policy.