• Hello MLAers! We've re-enabled auto-approval for accounts. If you are still waiting on account approval, please check this thread for more information.

Anyone up for some IIcx troubleshooting assistance? We have clocks but no activity...

GRudolf94 said:
Macs are crap for POST output: you either have the debug connector, which relies on the serial port/SCC, plus some via signals to indicate factory mode, or sound. You don't have sound hooked up, I'd plug that in because even glitching noises may help.
Click to expand...
I have had the speaker hooked up it does make a very faint click sound when i power up the board.
 
Thanks for the help everyone. I'm going to step away and take a nap.. Let me know if you get any ideas and ill jump back in when I am rested up.
 
I don't have a NuBus Mac II handy to check if they run hot at idle so no reference frame, but UC9 thru 12 being warm sounds kind of concerning. Those are the NuBus transceivers. If they were bad they could clamp the address and data lines low. What's on the pins?

ROMs are not the issue because the CPU isn't doing anything, and that includes trying to access the ROM. Unless of course they were all very bad and clamped all the data/address lines low.
 
GRudolf94 said:
I don't have a NuBus Mac II handy to check if they run hot at idle so no reference frame, but UC9 thru 12 being warm sounds kind of concerning. Those are the NuBus transceivers. If they were bad they could clamp the address and data lines low. What's on the pins?

ROMs are not the issue because the CPU isn't doing anything, and that includes trying to access the ROM. Unless of course they were all very bad and clamped all the data/address lines low.
Click to expand...
I’ll jump back on it and check again. I think they were all high any specific pins to check?
 
They can't all be high if the CPU lines are low. I mentioned tristate drivers earlier, those are the only ones the IIcx has, but they aren't what I was thinking of (some machines have drivers inbetween the CPU bus and the machine-side address/data buses). In any case, UD13-9 are what stick the CPU data into NuBus and vice-versa, and UC13-9 do the same for addresses (NuBus is multiplexed, i.e. it uses the same pins to provide address and data, at separate times).

The NuBus side can and should be high, but the machine-side should read the same as the CPU pins.
 
They are just slightly warm. About the same as the two oscillators y2 and y3.

Pin one of uc9 and uc10 both have 10mhz freq. all the rest are either high or floating.
 
Uc12 and 13 do not have a 10mhz clock on pin 1 hmmm. We have two more broken traces at pin 1 of UC 12 and UC 13.
 
To be clearer: the pins we care on these particular ICs are 13-20 (B side, facing CPU), and maybe 4-11, which is the A-side, facing NuBus. You have a broken trace/via there, UC12 and 13 have to be triggered off the same selection signals as 9 and 10. That signal on pin 1 is certainly correlated to the 10MHz NuBus clock.

However, those transceivers should not be selected at this moment, and so it's normal that things on the A-side be floating (and appear high because they're pulled up). NuBus uses negative logic, so asserted signals are low. UC/UD13-9 are inverting devices, so if one side is low, the other will be high.
 
GRudolf94 said:
To be clearer: the pins we care on these particular ICs are 13-20 (B side, facing CPU), and maybe 4-11, which is the A-side, facing NuBus. You have a broken trace/via there, UC12 and 13 have to be triggered off the same selection signals as 9 and 10. That signal on pin 1 is certainly correlated to the 10MHz NuBus clock.

However, those transceivers should not be selected at this moment, and so it's normal that things on the A-side be floating (and appear high because they're pulled up). NuBus uses negative logic, so asserted signals are low. UC/UD13-9 are inverting devices, so if one side is low, the other will be high.
Click to expand...
Yes I found the broken traces.
 
do you want me to map out each of the pins we care about? Most of them are high some are floating or just barely above zero.

I’ll fix these two broken traces
 
Do it on a couple ICs for a test. I still find it weird these devices would be hot/warm if not actually driving anything. Depending on what we see I may ask you to check a few of the control signals.

(theory: if the transceivers have broken traces on the control signals, they might be seeing themselves as selected in 'put inverted A on B' mode, and attempting to drive the machine side low from the pulled-high A side.)
 
GRudolf94 said:
Do it on a couple ICs for a test. I still find it weird these devices would be hot/warm if not actually driving anything. Depending on what we see I may ask you to check a few of the control signals.

(theory: if the transceivers have broken traces on the control signals, they might be seeing themselves as selected in 'put inverted A on B' mode, and attempting to drive the machine side low from the pulled-high A side.)
Click to expand...
GRudolf94 said:
Do it on a couple ICs for a test. I still find it weird these devices would be hot/warm if not actually driving anything. Depending on what we see I may ask you to check a few of the control signals.

(theory: if the transceivers have broken traces on the control signals, they might be seeing themselves as selected in 'put inverted A on B' mode, and attempting to drive the machine side low from the pulled-high A side.)
Click to expand...
Ok I’ll fix the broken traces and then tell you the state of each lower side pin on a couple. They are Definately not hot. Just a bit warm to the touch. Warmer than anything else on the board. I would say it’s a normal level of warmth but yes odd that they are warm at all.
 
Uc9

pin 13 - low
pin 14- low
pin 15- low
pin 16- low
pin 17- low
pin 18- low
pin 19- low
pin 20- low
pin 21- high
pin 22- low
pin 23- low
pin 24- high



Uc13

pin 13 - high
pin 14- high
pin 15- high
pin 16- high
pin 17- low
pin 18- high
pin 19- high
pin 20- low
pin 21- high
pin 22- low
pin 23- low
pin 24- high
 
You must log in or register to reply here.

Similar threads

davidg5678
No address/data bus activity. Is there a dead CPU in my Mac II?
Replies
2
Views
970
Addicted
A
David Cook
Sonnet Doubler Allegro for Mac II
2
Replies
23
Views
4K
ObeyDaleks
ObeyDaleks
K
SE/30 CPU only works when ROM isn't installed
Replies
2
Views
908
Kepler64Bit
K
J
Mac IIsi with no address or data bus activity. Strange signal on all ram data pins
Replies
11
Views
3K
JohnR
J
David Cook
Macintosh IIcx - Won't Power Down, then Won't Power Up, and SuperMac ColorCard is bad?
Replies
8
Views
2K
MacOSMonkey
M
Back
Top