Search found 33 matches

by kfro
Fri Aug 07, 2020 11:13 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Read through the last few posts and realised I'd missed you say that the reset to the CPU was good, so sorry about that. I agree, that tricky's ROM sounds like the best option. We could also try a very short looping program. I also read https://ist.uwaterloo.ca/~schepers/MJK/6502.html#2 that it's po...
by kfro
Fri Aug 07, 2020 5:24 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

I think we do not have a reliable reset to the CPU. Shorting the reset has proved that the 555 is working but I think we are not getting the reset from IC33 pin 4. Can we quickly test if this is going low when the reset switch is shorted.
by kfro
Thu Aug 06, 2020 10:08 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Thank Kazzie that will be useful IC6 is the video processor and it does get, hot, my machine has had a heat sink fitted for example. When you short the reset switch pad does IC16 pin 3 go high. I still think you have intermittent IC socket connections. My IC16 is in a socket and assuming yours is to...
by kfro
Thu Aug 06, 2020 9:16 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

If you do not have +5V on pins 4 and 8 you've lost the supply voltage.
by kfro
Thu Aug 06, 2020 9:11 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

You should have +5V on IC16 pins 4 and 8
pin 2 should go low when you press BREAK
pin 7 and 6 should go low when you press BREAK
pin 1 should be ground
pin 3 should go high when you press BREAK
by kfro
Thu Aug 06, 2020 7:34 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

So it looks like IC16 the 555 is the problem or one of it's passives, back in a bit need to have dinner
by kfro
Thu Aug 06, 2020 5:01 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

LOL, this machine is obviously a survivor if it's been through all that. We should do all we can you get it running again :D
by kfro
Thu Aug 06, 2020 10:37 am
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Agreed! I'm thinking that the clock issue maybe due to poor connections, either between scope probe and crusty pin or the normal dry joint, broken trace, IC socket contact, etc.. At some point all the socketed ICs need to be pulled and pins and sockets cleaned and some suitable contact clearer / pro...
by kfro
Wed Aug 05, 2020 10:58 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

ok, I'm fairly sure that pressing break etc should cause not reset on the CPU to go low momentarily. So what do you get on IC33 pin 3 if you press break?
by kfro
Wed Aug 05, 2020 8:49 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

sorry pin 5 should have been pin 6, pin 5 is not connected :shock:

The reset seems a little bit odd, it's not out of spec as such, but I'd really expect to see +5V. Can you check that it goes low when you press the BREAK key on the keyboard.
by kfro
Wed Aug 05, 2020 6:27 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Ok, IC7 is another ULA for the serial / Cassette interface. Make sure that the divided clocks on IC6 are there consistently. You could try flexing the board slightly and power cycling a few time. Once you are happy that they are good we should move on to seeing if the CPU (IC1) is running. Pin 8 - V...
by kfro
Wed Aug 05, 2020 5:13 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Yep, just found it, it's fed into the clock of IC86 pin 1 if S27 is in the north position. Also I suspect that we need to recheck pins 4, 5, 6 and 7 on IC6 for the divided clocks. We should see 1, 2, 4 and 8 meg clocks respectively.
by kfro
Tue Aug 04, 2020 10:32 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

So thinking about a clean input signal, I was thinking that this arrangement would shorten the duty signal, though I could not think why that would be required. For noise, I wonder if there is any reason why +ve noise would be more likely than -ve clocks like this suffer from problems like ringing ...
by kfro
Tue Aug 04, 2020 10:22 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

oh hang on the video ULA is IC6 not IC7
by kfro
Tue Aug 04, 2020 10:05 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Sorry, been in and out tonight. Yes try adding a link between IC40 pin 11 and pin 8 on the ULA.
by kfro
Tue Aug 04, 2020 9:10 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Yes this become the 16MHZ signal which goes to IC42 pin 2 See the resistor R102 and the capacitor C42. When the clock goes high, the cap will be charged up via the resistor. The time it takes the cap to charge is related to the capacitance times the resistance. The rule of thumb for the time it take...
by kfro
Tue Aug 04, 2020 7:56 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Yes, 13 will be difference because it's fed from an RC network. So that means there's a break somewhere between IC40 pin 11 and pin 8 on the ULA. Look for a dry joint, broken trace or if the chips are in sockets dirty pins or sockets.
by kfro
Tue Aug 04, 2020 7:03 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

That's good, it means it's probably not the ULA! What have you got on pins 11, 12 and 13 on IC40.

Yes I did mean connected to a PC via USB
by kfro
Tue Aug 04, 2020 5:34 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Just on my way out, but make sure you have 16MHz on pin 8 of the video ULA.
by kfro
Mon Aug 03, 2020 10:19 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Wow that was quick, I take ages to make up my mind of stuff like that. It will be interesting to see how it does. Yes a scan with a good magnifying glass is would probably be in order.
by kfro
Mon Aug 03, 2020 2:04 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

This looks interesting. The reviews are very good. https://www.amazon.co.uk/DOS1102-oscilloscope-Professional-Oscilloscope-Bandwidth/dp/B0833X3RFK/ref=sr_1_4?dchild=1&keywords=RIGOL+DS1054Z&qid=1596455939&sr=8-4 Yes looks ok at a glance, except for the mains cable issue, though that would be easy t...
by kfro
Mon Aug 03, 2020 12:51 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

When I started doing electronics again about two years ago after about a 35 year hiatus I looked at a bunch of different scopes. I ended up rejecting the PC based ones mainly because I wanted a dedicated instrument, that I could pick up and move around. In the end I bought the RIGOL DS1054Z. It's no...
by kfro
Mon Aug 03, 2020 12:25 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

ok, we are expecting to see 5 volts peak to peak. You get a lower reading on your meter because it's averaging, sorry should have explained that.
by kfro
Mon Aug 03, 2020 12:23 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

...and one other thing the little pot on the probe that you mentioned is not for vertical deflection (voltage) calibration it's for compensation. The idea is that you connected the prob to the "prob adj" test point and tweak the pot so that you have a nice square wave.
by kfro
Mon Aug 03, 2020 12:08 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

sorry done it again, at least we agree :-) I don't think there is much wrong with your scope to be honest. I think the main problem is that trying to look at a 16MHz square wave is right at the limit of what it can do, even when it was brand new. Here's the problem... A guy called Fourier managed to...
by kfro
Sun Aug 02, 2020 10:44 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

hehe just typed all this an then realised that Kazzie had already answered, but thought you may as well read it anyway... Ok, so you clearly have a 16MHz clock. There's a couple of things to check re the voltage readings you are getting. Your probe will have built in attenuation. Have a look at the ...
by kfro
Sun Aug 02, 2020 7:46 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Ah sorry, I completely missed that we where looking at the the IRQ and thought we where still looking at the 16MHz clock. I'm glad someone is awake! :oops:
by kfro
Sun Aug 02, 2020 6:11 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Ok, you have your time base (horizontal) set to 1 millisecond/div, you need to wind that clockwise 5 steps to 20 microseconds.

1 millisecond = 0.001 seconds
1 microsecond = 0.000,001 seconds

I think your scope is working fine :D
by kfro
Sun Aug 02, 2020 2:50 pm
Forum: 8-bit acorn hardware
Topic: Silent, nothing visible
Replies: 130
Views: 2826

Re: Silent, nothing visible

Is it the 9020P you have, only there seem to be a whole series of that scope dating over some time.
by kfro
Sun Aug 02, 2020 1:07 pm
Forum: 8-bit acorn hardware
Topic: Fastest way to arrange data on disc for database-type applications?
Replies: 7
Views: 374

Re: Fastest way to arrange data on disc for database-type applications?

Hi, From memory, and this is a very long time ago, both heads will be loaded at the same time. The reason being that in a floppy drive the head is in contact with the media. The media is a thin mylar sheet that would deform if not supported. On a double sided drive support is provided by the other h...

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