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Post by serafis on May 9, 2022 19:45:43 GMT -5
With IC152 removed, pins 83 and 84 of IC151 still both go to approx 3.3V when first turned on and no change when the main relay clicks
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Post by serafis on May 10, 2022 16:22:38 GMT -5
I also tested crystal X705 (10MHz) on IC154 pins 72 and 74. I get is around 3.28V on one leg, 3.02V on the other each leg (wrt GND), but no meaningful oscillation frequency on either leg or across the legs.
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Post by mastertech on May 10, 2022 18:32:59 GMT -5
Sorry about the delay. Weather has been nice here finally and I have lots to do outside. Anyways.
Ic151 seems to be dead. Crystals look to be running fine. USB CPU looks to be trying to communicate with it but with no response, hence the reset line constantly cycling.
But, it does not appear to be shorted like most failures usually seem to be. So it could just be locked up, possibly by something else.
Which now comes to that crystal not working on ic154 that you found. I would try swapping that crystal with the one from ic151 to rty to determine if it is the crystal or ic154.
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Post by serafis on May 10, 2022 18:54:05 GMT -5
Edit: I tried resetting the IC154 (SUB_MCU) by putting a 100 ohm resistor between CN11 Pin 4 (Reset) and Pin 1 (GND), after which the X705 correctly reads 10MHz (screenshot below). However, powering off and on again returns the crystal to its previous non-correct state. So maybe something wrong around IC154, or it's not getting its reset signal from IC151?  |
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Post by mastertech on May 10, 2022 19:12:26 GMT -5
Well that makes sense. IC151 is not resetting ic154.
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Post by serafis on May 10, 2022 19:12:58 GMT -5
There is continuity between Pin 61 of IC151 and Pin 82 of IC154 (SUB_MCU_RESET), as expected. On power up, this goes high (around 3.25V) once the mains relay clicks, but X705 measures incorrectly as described earlier. Jumping CN11 Pins 4 and 1 with 100 ohm resistor while powered on immediately makes X705 measure 10MHz correctly; Pins 82 of IC154 and 61 of IC151 remain high. If I jump IC164 to reset the unit, the same behaviour happens as if I power off and on again.
I don't know whether this tells us anything useful though!
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Post by serafis on May 10, 2022 19:19:50 GMT -5
I wonder what order IC151 is supposed to reset the various other ICs, e.g. Torino, DSP1, DSP2, DIR etc... and whether this happens before resetting IC154, and whether a failure in one of those ICs (maybe some of which are on the HDMI board) could cause IC151 to 'hang'... Just shooting in the dark here! And very hard to test the HDMI board in situ as it's mounted component-side down.
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Post by mastertech on May 10, 2022 19:57:22 GMT -5
At this point it is hard to say whether ic151 has failed or something else locking it up. About the only thing I can think of now would be to take your ohm meter and test every pin on ic151 looking for a short to gnd or close to short and then investigate if any show up. But you would have to check almost all pins except power and ground.
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Post by mastertech on May 10, 2022 20:28:20 GMT -5
I've been thinking about this some more. IC151 appears to be dead, however the crystals are running. So that is something. So then I was thinking about that reset line for ic151 cycling up and down and then I thought, it has to stop cycling for ic151 to run. So the constant cycling is probably preventing it from running properly. So now, 1) if this is incorrect, which I would think it is, which one is causing the problem? ic151 or ic162 which sends the reset signal. So the line in between the 2 must be severed to see. RN60, pins 1 or 5 looks to be the best way to sever that line if you can possibly lift a leg.
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Post by serafis on May 10, 2022 20:29:47 GMT -5
Only pins 3,13,63,73,75 and 81 show short to ground (as they should). Do you think this is a lost cause?
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Post by serafis on May 10, 2022 20:32:40 GMT -5
Snap, so was I. I'm thinking what might be happening is that when the USB is plugged in, IC162 sends a pull-down to TCN5_RESET (pin 82 on IC151) to reset it for a firmware update, waits for a correct response, doesn't get it so sends the reset pull-down again etc...
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Post by mastertech on May 10, 2022 20:35:50 GMT -5
Actually I am hoping c767 is bad and causing the cycling. Hoping.  |
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Post by serafis on May 10, 2022 20:59:24 GMT -5
Not sure how to test it - it's a tiny SMD. I could probably remove it but would have difficulty in putting it back! or to lift a leg of RN60 - it's even tinier!
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Post by mastertech on May 10, 2022 21:12:13 GMT -5
I was afraid of that. I would remove the cap first then. If it still cycles then maybe cutting the trace would be an option. You could later bridge solder the trace. Try to cut between resistor and ic162.
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Post by serafis on May 10, 2022 21:21:28 GMT -5
In the meantime.... I scraped and exposed the trace between IC151 Pin 82 and C767, and severed it in a way that I can (hopefully) rejoin it later with a blob of solder. I did the same for the trace between RN60 and C767. So IC162 Pin 21 is isolated from both C767 and IC151 Pin 82, which is also isolated from C767.
The scope shows Pin 82 of IC151 high, whether USB is plugged in or not, and pin 21 of IC162 high when no USB, and cycles when USB plugged in just as USB LED stops flashing. C767, now isolated, shows 1.07uF on the capacitance meter.
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