Help with two Orics

If you want to ask questions about how the machine works, peculiar details, the differences between models, here it is !
How to program the oric hardware (VIA, FDC, ...) is also welcome.
User avatar
iss
Wing Commander
Posts: 1258
Joined: Sat Apr 03, 2010 5:43 pm
Location: Bulgaria
Contact:

Re: Help with two Orics

Post by iss »

Congrats for all your success - two working Orics is real treasure!
About the power-on failure: there should be difference depend on what you first plug.
For better results try first to plug the PSU adapter in the AC mains and then plug the barrel jack in Oric.
Next try also in opposite order (first plug the jack in Oric and then plug the PSU adapter in AC) to compare the number of the successful boots ;).

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

^I’d say it varies, but with after being shut down for a longer period like overnight, it is more likely that the TV can’t sync with the Oric’s signal when turned on from the mains side than when it’s been turned on from the DC side. If it warms up, also mains side power cycle can produce a stable picture.

There are times when TV shows a blank picture at bootup, instead of a rolling garble and there’s just a buzz from the internal speaker of the Oric.

I measured the voltage from the reset pin of the CPU and it went from 0 to 4,96 V.

User avatar
mikeb
Flight Lieutenant
Posts: 282
Joined: Wed Sep 05, 2018 8:03 pm
Location: West Midlands, UK
Contact:

Re: Help with two Orics

Post by mikeb »

protek wrote:
Thu Jun 04, 2020 7:39 pm
I forgot to tell where I got the reset pin being high. I used my logic probe for that. I didn’t see any change in that during the power cycle.
First observation, where did the processor come from? It looks like a "6502" (which is 1MHz part and doesn't work in Oric, needs a 6502A!) so try swapping that for an actual 6502A. Your 6522 is an A, which is good. This is because although Oric is a 1MHz machine, the clock is run at an unusual duty cycle, meaning the 6502 has to work at an equivalent to about 1.5MHz, to leave space for the ULA to dive in.

Your logic probe won't show the reset at power up -- if the probe is powered from the board, it will be "stunned" by the power being applied and never notice it. It probe is externally powered, it should at LEAST report the line going from floating or low, to high -- otherwise, when Oric is not powered, how can the line be high? :)

Re: your tynemouth link, "and after a second or so" -- no -- far faster than that on the reset. The circuit may be basic, but throwing extra inverters and 555 chips and all sorts is not necessary. Using a microcontroller just to create a reset pulse is either insane, or showing off :) either way totally unnecessary. Sure, you could engineer a better reset circuit. But remember, this one capacitor, one resistor worked on every Oric ever made, and for most of them, still does :)

User avatar
mikeb
Flight Lieutenant
Posts: 282
Joined: Wed Sep 05, 2018 8:03 pm
Location: West Midlands, UK
Contact:

Re: Help with two Orics

Post by mikeb »

protek wrote:
Fri Jun 05, 2020 5:51 am
I measured the voltage from the reset pin of the CPU and it went from 0 to 4,96 V.
That's your reset, right there :)

Of course what you can't see is that it goes from 0 to 4.96V a little slower than the 5v rail does it.

That's the point though, while held low, the 6502 is stopped and does not run, and is released at this crosses some threshold (as any digital signal behaves when it is ambiguously ramping up from 0 to 1).

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

mikeb wrote:
Fri Jun 05, 2020 6:12 pm

First observation, where did the processor come from? It looks like a "6502" (which is 1MHz part and doesn't work in Oric, needs a 6502A!) so try swapping that for an actual 6502A. Your 6522 is an A, which is good. This is because although Oric is a 1MHz machine, the clock is run at an unusual duty cycle, meaning the 6502 has to work at an equivalent to about 1.5MHz, to leave space for the ULA to dive in.
The CPU is the same that was soldered directly onto the mainboard previously. I do apologize about the low resolution of the pictures, but it does say 6502AP on the top row.

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

mikeb wrote:
Fri Jun 05, 2020 6:15 pm
protek wrote:
Fri Jun 05, 2020 5:51 am
I measured the voltage from the reset pin of the CPU and it went from 0 to 4,96 V.
That's your reset, right there :)

Of course what you can't see is that it goes from 0 to 4.96V a little slower than the 5v rail does it.

That's the point though, while held low, the 6502 is stopped and does not run, and is released at this crosses some threshold (as any digital signal behaves when it is ambiguously ramping up from 0 to 1).
So, basically, in an ideal situation, should the the 6502 wait just a little bit longer before crossing that threshold? Or should I just simply try another 6502A?

User avatar
mikeb
Flight Lieutenant
Posts: 282
Joined: Wed Sep 05, 2018 8:03 pm
Location: West Midlands, UK
Contact:

Re: Help with two Orics

Post by mikeb »

protek wrote:
Fri Jun 05, 2020 6:49 pm
The CPU is the same that was soldered directly onto the mainboard previously. I do apologize about the low resolution of the pictures, but it does say 6502AP on the top row.
Ah, you got me there :) I could only read the longer middle line ending in 6502-I3, and did not process the top line being AP (Version A, plastic)!
protek wrote:
Fri Jun 05, 2020 6:49 pm
So, basically, in an ideal situation, should the the 6502 wait just a little bit longer before crossing that threshold?
Sort of -- for reset problems, usually the power supply is still not fully stable when the 6502 attempts to start, causing it to misbehave/crash. Either :-

1) The power supply is TOO SLOW in getting stable -- as posted in a previous message, it can be the difference between whether you switch on the PSU at the wall, THEN connect Oric, or connect Oric, then switch on at the wall. Or finding a power supply that doesn't sag when Oric is first connected!

2) ... or the reset circuit is TOO FAST in releasing the processor -- usually the capacitor is old and has reduced in value, allowing it to charge too fast, so going off early.

(Or both!)

The threshold when "low becomes high" is fixed in the 6502, it's a digital input being fed with an analog (rising) signal. I doubt changing processor would vary that behaviour much, and if you really want to extend the reset pulse, I suppose a 10uF capacitor would *really* make sure :)

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

^So, the manual reset pulls it momentarily low and it then goes high again, right?

A 10 uF capacitor takes longer to charge, I assume? I have to see, if I have a 10 uF lying around.

User avatar
mikeb
Flight Lieutenant
Posts: 282
Joined: Wed Sep 05, 2018 8:03 pm
Location: West Midlands, UK
Contact:

Re: Help with two Orics

Post by mikeb »

protek wrote:
Sun Jun 07, 2020 2:12 pm
^So, the manual reset pulls it momentarily low and it then goes high again, right?

A 10 uF capacitor takes longer to charge, I assume? I have to see, if I have a 10 uF lying around.
Yes, much like the circuit for the other (NMI) reset button. That is a switch (to ground) and a pullup resistor (to 5V).

For the power on/cold reset, the discharged capacitor acts as a short circuit at power on, and as it charges, it becomes an open circuit. So like a slowly opening switch.

Shorting the reset line to ground just forcibly discharges the capacitor, and drags the line low, allowing it to repeat the process.

To test, you can just add the 10uF in parallel (get the positive and negative legs the same way round!) which will give you 11uF :)

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

I tested with a (used) 10 uF capacitor. That unfortunately didn’t help with the boot issue, although I can see that it takes more time to boot when I force the reset.

I think I need to address the other boot issue, before I continue with the reset line. Regardless, whether I do a cold reboot from the mains or the DC side, board #2 is only able to produce a picture that the TV is able to synch with maybe 1 out of 5 times. Most of the times the TV just receives the blanking signal, but no stable picture. I really haven’t been able to come up with a reason. Many times, there’s an audible buzz from the board’s loudspeaker when it can’t synch. Getting a stable garbled image just seems to be completely random. I really can’t think of anything else than a bad solder joint somewhere.

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

I reflowed the solder joints for the sockets I have installed previously. No help. I tried the diagnostic ROM for a change. The board wouldn’t synch with the TV at all. I changed the Basic ROM back. Same thing. Can’t get a picture out of it. Just buzzing.

User avatar
mikeb
Flight Lieutenant
Posts: 282
Joined: Wed Sep 05, 2018 8:03 pm
Location: West Midlands, UK
Contact:

Re: Help with two Orics

Post by mikeb »

A loss of vertical sync at the TV, "rolling garble" as you called it, can be normal (the ULA has picked up a 60Hz attribute by accident) and this should clear when BASIC starts. This seems to be more likely when DRAM chips have been replaced with non-originals, but is harmless.

A completely blank/black screen is weird. This always corresponds with a buzzing sound from the Oric speaker?

Can you tell if this buzzing is the sort of 50Hz/100Hz buzz you get from mains hum (like if you accidentally touch an amplifier input with a finger).

If it is, then I'd be wary that the power supply has a big ripple in it for some reason, and it's getting through into the voltage rail/LM386 amplifier chip.

But otherwise, when you get the blank screen/buzz, it would be useful to know if the 12MHz clock into the ULA (and 1MHZ out) are present and correct -- the ULA pretty much HAS to output some kind of picture, a blank screen takes work :) So no power, no clock ... (and no amount of resetting the CPU can get you out of that one, as you note!)

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

I tried measuring the clock frequencies with my el cheapo handheld oscilloscope, but apparently it is not up to the task.

I did notice that if I short pin 13 of the hex inverter, I can get the stable carbage picture on TV and then force the boot by shorting the reset line. I think the 74HC04 that is currently on board #2 isn’t the best choice for generating the clock signal for the ULA. I’ve already ordered a 74LS04 to replace it.

User avatar
mikeb
Flight Lieutenant
Posts: 282
Joined: Wed Sep 05, 2018 8:03 pm
Location: West Midlands, UK
Contact:

Re: Help with two Orics

Post by mikeb »

protek wrote:
Thu Jun 11, 2020 11:29 am
I tried measuring the clock frequencies with my el cheapo handheld oscilloscope, but apparently it is not up to the task.
That's poor, it's not like it's super high frequency -- is it an "audio grade" one or something? Alternatively, it could be there's nothing there to measure ...
protek wrote:
Thu Jun 11, 2020 11:29 am
I did notice that if I short pin 13 of the hex inverter, I can get the stable carbage picture on TV and then force the boot by shorting the reset line. I think the 74HC04 that is currently on board #2 isn’t the best choice for generating the clock signal for the ULA. I’ve already ordered a 74LS04 to replace it.
Short pin 13 to ... what? Ground? Another pin? Either way, sounds like you kicked the oscillator into action, which is a good sign.

Original part was SN74LS04, so this might help.

It's electronics. Amplifiers oscillate, and oscillators won't. I think you just found the 2nd part to be true :

User avatar
protek
Pilot Officer
Posts: 100
Joined: Wed May 23, 2018 9:10 pm
Location: Oulu, Finland

Re: Help with two Orics

Post by protek »

^To ground, yes. The RF modulator case to be exact.

Post Reply