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RE: dead modem? - psypher - 05-23-2020

(05-23-2020, 05:11 PM)admin Wrote: There are two chips that handle serial and SCSI.  The 85C30 just does the serial.  The 53C80 is the SCSI controller.  It's funny that these two chips have these numbers, and they are often confused between each other.
so should i be looking for a different chip? the AM85C80 datasheet says its a combined SCSI Controller and Serial Communications Controller and with the number close to 85C30 I thought that would be it but if its not (and that would be great because that chip looks like a pain to get off) would you know where I should be looking?


RE: dead modem? - admin - 05-24-2020

Ah... I thought it was a 85C30 (not a C80).  I had not seen that chip before!  Typically every Mac I have ever worked with uses a separate 53C80 and 85C30 chips.

Yeah, that is going to be tough to get off the board without the proper equipment.  Did you make a new 8 pin serial cable for the loop back test or use the same cable you had?  Maybe your cable is bad?


RE: dead modem? - psypher - 05-24-2020

(05-24-2020, 12:39 AM)admin Wrote: Ah... I thought it was a 85C30 (not a C80).  I had not seen that chip before!  Typically every Mac I have ever worked with uses a separate 53C80 and 85C30 chips.

Yeah, that is going to be tough to get off the board without the proper equipment.  Did you make a new 8 pin serial cable for the loop back test or use the same cable you had?  Maybe your cable is bad?
i didnt make a new 8 pin cable but i did test mine with  multi meter and it seems ok. by proper equipment do you mean a hot air rework station? i dont have one but i have been thinking of getting one. of course then there is the whole not having a spare chip, i have one on a parts board but that board had some major battery leakage so its not a 100% if it would be good.


RE: dead modem? - admin - 05-24-2020

Yeah, you need an IR or hot air pencil to be able to remove that chip. Battery leakage won't affect the chips, just the PCB itself. You might want to try to find a new cable just in case your cable has an intermittent connection and it just so happens to tone out with our multi meter while you are testing it. Extra cables are cheap compared to going through the process of replacing a chip that might be good. You could also try to locate the Rx and Tx lines on the motherboard itself and jumper those together.


RE: dead modem? - psypher - 05-24-2020

(05-24-2020, 10:51 AM)admin Wrote: Yeah, you need an IR or hot air pencil to be able to remove that chip.  Battery leakage won't affect the chips, just the PCB itself.  You might want to try to find a new cable just in case your cable has an intermittent connection and it just so happens to tone out with our multi meter while you are testing it.  Extra cables are cheap compared to going through the process of replacing a chip that might be good.  You could also try to locate the Rx and Tx lines on the motherboard itself and jumper those together.
couldnt i just use some legs of an old part, say a capacitor, and stick it into the port in the back of the machine and jump them there. at least i would know my cable is ok.


RE: dead modem? - admin - 05-25-2020

Yes, if you can do that make and sure there is good continuity that would work.


RE: dead modem? - psypher - 05-27-2020

(05-25-2020, 11:30 AM)admin Wrote: Yes, if you can do that make and sure there is good continuity that would work.
so i haven't got around to doing further testing yet, but i just wanted to say thank you for all the help. this is way more support than i was expecting. thanks again!


RE: dead modem? - admin - 05-27-2020

Well, it stinks that it worked fine for months. Really I hope it was my product that failed (there is a lifetime warranty) as that would be a simple solution compared to what you could be facing! Let me know what you find.


RE: dead modem? - psypher - 06-01-2020

ive been doing more testing with my classic ii logic board and the schematic and everything is checking out, which is good, but in my testing I rechecked the cable and it seems that pins 6 (TxD+) and 8 (RxD+) are not getting tone from the 25 pin end. this was a new cable I bought at the same time I got the modem is it possible that it would have failed and what kind of failure are we talking about? just curious as I havent seen a cable, aside from physical damage fail. also would that explain the snooper test fail? when I ran the test I tried it with the modem plugged in and with out the modem plugged in. in both cases it failed, if nothing is plugged in would it fail regardless? I thought I read something that said it could do loop back in software but not sure if that was correct.


RE: dead modem? - admin - 06-01-2020

If the cable does not tone out to the DB25 then that is an issue for sure! I have seen cheap cables fail just from bending the cable back and forth over time.

Snooper requires a loopback cable (TxD connected to RxD).