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Old 26th May 2022, 9:31 am   #161
ajgriff
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Default Re: Perth PET

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Originally Posted by SiriusHardware View Post
That's up to you, you know our philosophy was always to try to establish reasonable doubt before replacing something ....
I think you've put forward the case in favour of 'reasonable doubt' very succinctly. Given that a spare chip plus socket are to hand it's got to be worth a try.

Alan
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Old 26th May 2022, 12:27 pm   #162
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Default Re: Perth PET

The official documentation for this scope is (to put it politely) sparse.

OpenHantek has better docs - here:

https://github.com/OpenHantek/OpenHa...ser_Manual.pdf

But I can find no mention in there of any external triggers. There is a port on the device marked USBXI but Goggle isn't helping me much with that, nor is it mentioned in any of the documents.

Colin.


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That's up to you, you know our philosophy was always to try to establish reasonable doubt before replacing something but those buffers have a poor reputation for reliabilty so it might not be a bad idea to make it easy to rule that chip out on this and any future occasions. When UE10 had failed last time around, it did so in a way which was only affecting data coming from the buffered data bus to the unbuffered data bus - the unbuffered data bus was not affected by the fault on UE10 so it didn't stop the test code from running.

The conjecture this time is that a fault on one of UE9's CPU-side elements could be interfering with the databus on the unbuffered side, corrupting the data flowing from the PROMs to the CPU and preventing code in the PROMs from being run.

I was thinking we might try scoping the data bus in a more scientific way before replacing UE9, can you say whether your scope only has two inputs, does it by any chance have an EXT TRIG input in addition to the channel 1 / channel 2 inputs? I'll check back in for the answer tomorrow.
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Old 26th May 2022, 12:42 pm   #163
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Default Re: Perth PET

I think USBXI provides a means of networking devices so won't help much in this instance. As far as I know the Hantek has two channels but no external trigger facility.

Alan
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Old 26th May 2022, 3:53 pm   #164
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Default Re: Perth PET

Dammit. UE9 replaced and no change.

Colin.
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Old 26th May 2022, 4:16 pm   #165
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Default Re: Perth PET

Never mind, it was worth a shot and at least narrows down the possibilities. Will make future fault finding easier too.

Alan
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Old 26th May 2022, 5:30 pm   #166
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Default Re: Perth PET

I think we are going to have to look more closely at the data bus but before we do let's just check that the address lines are going all the way to the PROM pins. We have only followed them to the outputs of the UE9 / UE10 buffers so far.

Reinstall the original PROMs and refit the NOP rig.

Scope the following PROM pins, check that the frequencies on them are as given below and also check that all of the waveforms going to these pins are clean and full height.

Code:
on UD6, UD7, UD8, UD9, pin 8, 250Khz
on UD6, UD7, UD8, UD9, pin 7, 125Khz
on UD6, UD7, UD8, UD9, pin 6, 62.5Khz
on UD6, UD7, UD8, UD9, pin 5, 31.25Khz
on UD6, UD7, UD8, UD9, pin 4, 15.63Khz
on UD6, UD7, UD8, UD9, pin 3, 7.813Khz
on UD6, UD7, UD8, UD9, pin 2, 3.096Khz
on UD6, UD7, UD8, UD9, pin 1, 1.953Khz
on UD6, UD7, UD8, UD9, pin 23, 976.6Hz
on UD6, UD7, UD8, UD9, pin 22, 488.3Hz
on UD6, UD7, UD8, UD9, pin 19, 244.3Hz
on UD6, UD7, UD8, UD9, pin 18, 122.1Hz
If that's all OK then remove the NOP rig and fit the CPU directly. With power off, measure continuity between the following pairs of IC pins, directly on the IC pins themselves.

Code:
CPU pin		UD9 pin	
33		9
32		10
31		11
30		13 * note UD9 pin 12 is skipped
29		14
28		15
27		16
26		17
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Old 26th May 2022, 6:00 pm   #167
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Default Re: Perth PET

Continuity first - all checks out. Would a resistance reading be useful?

Colin.
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Old 26th May 2022, 6:39 pm   #168
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Default Re: Perth PET

Not generally, as 'continuity' implies very low or no resistance. If the resistances are <2 ohms including the resistance of your meter leads, that would be a pass. Anything higher would be 'a measurement of interest'
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Old 26th May 2022, 6:49 pm   #169
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Default Re: Perth PET

I must admit that I rarely use a meter's continuity feature for this sort of thing, preferring to measure the actual resistance. As long as the reading is less than a couple of Ohms everything should be fine allowing for lead and contact resistance. Posts crossed.

Alan
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Old 26th May 2022, 6:54 pm   #170
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Default Re: Perth PET

True, there are pros and cons for using the 'continuity' feature of a meter depending on whether it is stand-alone or combined with something else.

Continuity on a switch position on its own usually indicates the resistance anyway and buzzes as long as the resistance is below a certain ohms figure but that threshold can be quite high, so I always look at the reading in addition to listening for the buzz.
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Old 26th May 2022, 6:56 pm   #171
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Default Re: Perth PET

All less than 2 ohms so that seems to be ok.

This flippin NOP device falls apart every time I look at it. You'll have to wait a little while I'm afraid.
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Old 26th May 2022, 7:00 pm   #172
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Default Re: Perth PET

My first meter (analogue then of course) didn't have a continuity/diode function so I've never bothered with such things since!

Alan
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Old 26th May 2022, 7:04 pm   #173
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Default Re: Perth PET

OK - if you are reworking it anyway, the power pickup leads you currently have going from the NOP rig to UG4 pads - your life might be easier if you took those to the NOP rig's CPU socket pin 8 (for +5V) and the NOP rig's CPU socket pin 1 (for 0V). That would make it easier to insert or completely remove the NOP rig.
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Old 26th May 2022, 7:35 pm   #174
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Default Re: Perth PET

Have to disappear for the evening, sorry - SWMBO has a technical emergency which requires my assistance - 70 miles away!
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Old 26th May 2022, 9:51 pm   #175
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Default Re: Perth PET

That's OK. I'll try to get some kind of report back later on.

Don't ever ask for a photo of my NOP device. Even I'm embarrassed.

And it's my birthday tomorrow so don't expect anything too coherent tomorrow.

Colin.
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Old 26th May 2022, 10:25 pm   #176
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Default Re: Perth PET

OK - all ROMs are showing the frequencies as above on all pins.

Couple of questions:

1) what voltage should the pins be showing when powered on with the NOP device fitted?
2) Pin 12 on UD9 does not connect to earth as the schematics say it should (page 4) but to a capacitor - C9; is there a reason that the schematics don't show this?

Colin.
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Old 26th May 2022, 10:51 pm   #177
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Default Re: Perth PET

Pin 12 on UD9 should be connected to ground. The capacitor is probably a decoupling capacitor connected between ground and 5v.

Check continuity between Pin 12 on UD9 and pin 12 on the other proms, or some other known 0v ground.
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Old 26th May 2022, 10:59 pm   #178
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Default Re: Perth PET

IC decoupling capacitors are quite often omitted from complex schematics. Their presence is just assumed. I think you'll find that there is continuity between Pin 12 and earth even though you can't see the connection to the PCB ground plane. Have a good day tomorrow Colin!

Alan
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Old 26th May 2022, 11:10 pm   #179
ScottishColin
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Default Re: Perth PET

This is what's confusing me. I get continuity to the one of the capacitor legs, but not to either ground or any of the other pin 12s.

Colin.


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Pin 12 on UD9 should be connected to ground. The capacitor is probably a decoupling capacitor connected between ground and 5v.

Check continuity between Pin 12 on UD9 and pin 12 on the other proms, or some other known 0v ground.
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Old 26th May 2022, 11:24 pm   #180
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Default Re: Perth PET

Then you might have found a fault. Add a wire link from the capacitor pin that connects to UD9 pin 12 and pin 12 of one of the other proms.
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