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Schematics for Power Mac 7600?
Posted by: Byte Knight on 2023-12-09 14:52:01
Does anyone have the schematics for the PowerMac 7600's logic board? I've got a modem port that doesn't work, but the printer port works fine.
Posted by: Phipli on 2023-12-09 15:27:09
Does anyone have the schematics for the PowerMac 7600's logic board? I've got a modem port that doesn't work, but the printer port works fine.
The 7500, 8500, 7300 and 8600 schematics should be very similar too. I think the 7500 and 8500 will be identical effectively, the 7300 and 8600 will only be a little different.
Posted by: Phipli on 2023-12-09 15:28:39
Truth be told though, if one of your serial ports doesn't work, it's only going to be a very small number of things, so I'm not sure you really need a schematic.
Posted by: Byte Knight on 2023-12-09 16:56:47
Truth be told though, if one of your serial ports doesn't work, it's only going to be a very small number of things, so I'm not sure you really need a schematic.
Ok, so here's the deal - the data in is fine as I can see my wifi modem booting up and connecting to wifi, but there's no data out as I can't type in any "at" commands. Everything works fine from the printer port. Continuity from the modem port lines to the DS8925M chip at U4 are good and match the printer port lines to the twin DS8925M chip. I just tried replacing the DS8925M chip without any luck. I'll replace the caps in the area next to see if that might fix it, but I'm not too optimistic since the printer port works fine...
Posted by: GRudolf94 on 2023-12-09 18:39:32
Modem ports are usually victims to lightning strikes. The 8925 was a good try anyway. Have you checked continuity from the jack pins, though? Sometimes the problem lurks inside the miniDIN itself.
Posted by: Byte Knight on 2023-12-09 20:29:52
Modem ports are usually victims to lightning strikes. The 8925 was a good try anyway. Have you checked continuity from the jack pins, though? Sometimes the problem lurks inside the miniDIN itself.
Interesting about the lightning strikes. And yes, I tested continuity through the port.
Posted by: Phipli on 2023-12-10 01:47:09
From the 8925 it likely just goes on to the Curio chip, but check for shorted or open circuit passives between the 8925 and the port and 8925 and Curio. Check the 8925 power as well.

But first, what cable are you using? The most basic setup is a straight serial mini DIN cable between two macs. Modem cables can be wired incorrectly, so I'd test the port using something else first. Just in case.
Posted by: Byte Knight on 2023-12-10 14:32:30
From the 8925 it likely just goes on to the Curio chip, but check for shorted or open circuit passives between the 8925 and the port and 8925 and Curio. Check the 8925 power as well.

But first, what cable are you using? The most basic setup is a straight serial mini DIN cable between two macs. Modem cables can be wired incorrectly, so I'd test the port using something else first. Just in case.
It's not the modem cable - it works fine with my other Macs and I tried another one just to be safe and got the same results.

Thanks for the suggestions, but without the schematics I'm not sure how I'm going to be able to check connections between those two chips, at least with my limited abilities...
Posted by: GRudolf94 on 2023-12-10 15:11:39
Measuring my 8100's serial ports against Curio - translating these to 8925 pinouts is gonna be up to you, but doable using the datasheet and beeping out ports against that, the 8100 unfortunately uses 26LS30/32

Curio pin | Signal name on miniDIN, converted to single-ended
130 REQ_A
131 DTR_A
132 RTS_A
133 HSKI_A
134 GPI_A
3 RTXC_A
4 RXD_ A
5 TRXC_A
6 TXD_A

136 RTS_B
137 HSKI_B
138 RTS_B
139 REQ_B
140 DTR_B
142 TXD_B
143 TRXC_B
144 RXD_B
145 RTXC_B

A on there is Modem, B is Printer, YMMV
Posted by: joshc on 2023-12-10 19:45:09
@Arbee do 7600 schematics happen to be ones you might have?
Posted by: Arbee on 2023-12-11 07:14:44
I have 6500, 7200, and 9600 for 60x PCI.
Posted by: Phipli on 2023-12-11 07:39:27
I have 6500, 7200, and 9600 for 60x PCI.
9600 would be close enough for them if you're happy to share it here Arbee.
Posted by: Byte Knight on 2023-12-11 12:15:45
Measuring my 8100's serial ports against Curio - translating these to 8925 pinouts is gonna be up to you, but doable using the datasheet and beeping out ports against that, the 8100 unfortunately uses 26LS30/32
Thank you for measuring all of those!
Posted by: Arbee on 2023-12-11 16:59:18
Here you go.
Posted by: Phipli on 2023-12-11 20:28:41
Here you go.
Thanks Arbee. @Byte Knight designations will likely be different, but the arrangement should be the same as this :

1000014673.jpg


1000014674.jpg
Posted by: Byte Knight on 2023-12-12 07:10:43
Thanks Arbee. @Byte Knight designations will likely be different, but the arrangement should be the same as this :
Awesome - thanks to both of you!
Posted by: Byte Knight on 2023-12-12 12:46:58
Thanks Arbee. @Byte Knight designations will likely be different, but the arrangement should be the same as this :
Voltage is good to the 8925, and all the lines to the Curio are good. I just can't figure out where the GCRTSA line from the 8925 goes from the schematics...
Posted by: Phipli on 2023-12-12 12:50:39
Voltage is good to the 8925, and all the lines to the Curio are good. I just can't figure out where the GCRTSA line from the 8925 goes from the schematics...
Goes to pin 149 on U16 "Grand Central".

Sheet 15. The numbers in brackets are the sheets the trace goes to, Sheet 25 and 26 are test points.
Posted by: Byte Knight on 2023-12-20 17:58:21
Goes to pin 149 on U16 "Grand Central".

Sheet 15. The numbers in brackets are the sheets the trace goes to, Sheet 25 and 26 are test points.
That checks out too.

So I got another working 7600 logic board and get the same results, so maybe it's not a serial port issue. If I fire up the latest PPC version of ZTerm v1.1b7, I can't select either one of the serial ports. If I use the 68k version of ZTerm v1.01, the modem port doesn't send but it can receive, and I can select the printer port which works completely fine with my WiModem232. White Knight works with the printer port only. Black Night doesn't work with either of the serial ports. Can anyone else confirm this behavior with their 7600 serial ports?
Posted by: jajan547 on 2023-12-20 23:52:07
I have 6500, 7200, and 9600 for 60x PCI.
can you drop the 7200 and 6500 too? Thanks in advance 🙂
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