Search found 45 matches

by mikeb
Tue Mar 19, 2019 6:36 pm
Forum: Technical questions
Topic: Oric Atmos Won't Initialise
Replies: 14
Views: 358

Re: Oric Atmos Won't Initialise

Just to be clear ... the tracks I was talking about cutting are large, easy to cut, easy to repair, GND voltage rails, and purely for the purpose of isolating the fault, so that chip replacement can be targetted to the (hopefully single) faulty chip. To remove even a single 14 pin DIP chip from a bo...
by mikeb
Mon Mar 18, 2019 6:50 pm
Forum: Technical questions
Topic: Oric Atmos Won't Initialise
Replies: 14
Views: 358

Re: Oric Atmos Won't Initialise

Probably not entirely with a logic probe (which will only tell you low, high, high-Z (floating) or pulsing). Again, unless you get lucky :) Oscilloscope might be handy if you have access to one? With the DRAM, you have 8 "identical" chips. You can compare the states of the corresponding legs on each...
by mikeb
Sun Mar 17, 2019 6:46 pm
Forum: Technical questions
Topic: Oric Atmos Won't Initialise
Replies: 14
Views: 358

Re: Oric Atmos Won't Initialise

Same thing had happened to my Oric in the past. The reason was a failed ram chip. I replaced it and it worked fine.. Maybe you could consider this.. It's likely it is -- but finding which one is hard. If you get lucky, the failed one heats up. We've already established that the memory chips aren't ...
by mikeb
Sat Mar 16, 2019 6:48 pm
Forum: Technical questions
Topic: Oric Atmos Won't Initialise
Replies: 14
Views: 358

Re: Oric Atmos Won't Initialise

+1 on the repair guide link ... ;) The RESET switch (NMI) is edge-triggered, isn't it? So if it was stuck, open or closed, it wouldn't stop oric working. It just wouldn't warm-reset. The reset circuit (power up, cold boot) is a different thing, and I've found before that an Oric that is powered up w...
by mikeb
Thu Mar 14, 2019 6:07 pm
Forum: Technical questions
Topic: Replace XT1 and XT2 crystals
Replies: 8
Views: 326

Re: Replace XT1 and XT2 crystals

Repair shop with really big soldering irons :) I don't have a highlighted 5v rail, and that's connected to the letters -- it was a picture borrowed from my Oric Repair notes. It indicates good places to cut the 0v rail to isolate faulty parts that are overloading the power rail. It's a hand-annotate...
by mikeb
Wed Mar 13, 2019 6:38 pm
Forum: Technical questions
Topic: Replace XT1 and XT2 crystals
Replies: 8
Views: 326

Re: Replace XT1 and XT2 crystals

The underside of XT2 looks like someone has desoldered/replaced this XTAL using an inappropriately large soldering iron, and failed to clean the flux up. It's messy as anything, lots of scraping about :) The extra solder blobs/pads you mention -- I'm guessing, but if you mean the two silver pads at ...
by mikeb
Mon Mar 11, 2019 6:48 pm
Forum: Technical questions
Topic: Replace XT1 and XT2 crystals
Replies: 8
Views: 326

Re: Replace XT1 and XT2 crystals

You mention different types but the service manual simply states 'XTAL 12MHz' so I'm guessing it would be the most common option I did look in the service manual to see if there was a hint or a part number. But no :( As @iss says, go with an easily available small part and try it. Once you've got t...
by mikeb
Sun Mar 10, 2019 8:59 pm
Forum: Technical questions
Topic: Oric Microdisc: Master/Slave selection
Replies: 11
Views: 312

Re: Oric Microdisc: Master/Slave selection

FYI: The cable-partial-twisting thing was mostly only used on PCs, where the Shugart spec was slightly bodged/ignored, and it meant that you jumpered both drives the same -- the twist in the cable swapped over the drive selects/motor on lines between drive A and B. In the process, it meant you could...
by mikeb
Sun Mar 10, 2019 8:44 pm
Forum: Technical questions
Topic: Replace XT1 and XT2 crystals
Replies: 8
Views: 326

Re: Replace XT1 and XT2 crystals

Oh yes. XT1 (12 MHZ) is the main oscillator, from which all other clocks derive. No CPU, no ULA, nothing of any use. XT2 is only needed IF you want a PAL colour output on the UHF modulator. It does have to be exactly 8.8672375 MHz or the colour carrier frequency will be wrong. Edit to add: It is twi...
by mikeb
Wed Feb 27, 2019 6:12 pm
Forum: Technical questions
Topic: Dead oric 1
Replies: 48
Views: 1769

Re: Dead oric 1

Might be a silly suggesteion but have you tested the multimeter to check that it isnt showing eratic values. New batteries perhaps. I'm not sure how it would be possible to get 7v from the 7905 otherwise. I did mention to check the multimeter in my first post. Previously it was reading 4.2v on 5v r...
by mikeb
Mon Feb 25, 2019 5:53 pm
Forum: Technical questions
Topic: Dead oric 1
Replies: 48
Views: 1769

Re: Dead oric 1

@ibisum -- you don't "give things amps". You give things volts. They draw whatever amps they feel like, up to the point the power supply expires or shuts down under overload. It's an original Oric power supply, so it should be capable of powering an Oric. No wait, it is capable, as it powers another...
by mikeb
Sun Feb 24, 2019 9:33 pm
Forum: Technical questions
Topic: Dead oric 1
Replies: 48
Views: 1769

Re: Dead oric 1

It's not about whether the PSU works on your other Oric (although that's good to know!) -- it's about how much current is drawn by the faulty Oric when connected to a power supply. If excessive current is being drawn, that could well be the reason your 5v line is low, and changing the regulator woul...
by mikeb
Sat Feb 23, 2019 7:33 pm
Forum: Technical questions
Topic: Dead oric 1
Replies: 48
Views: 1769

Re: Dead oric 1

Oh well, sometimes you get really lucky and find one DRAM chip is toasting! The question (further above) asking you to check the current drawn -- that's useful information, so let us know when you measure it! If you do unbolt and unsolder the regulator, make sure to fold the legs correctly to hit th...
by mikeb
Fri Feb 22, 2019 6:31 pm
Forum: Technical questions
Topic: Dead oric 1
Replies: 48
Views: 1769

Re: Dead oric 1

I can confirm that your 4.2v is too low -- make sure your multimeter has a fresh battery though, as a lot of handheld DMMs read funny when the battery is going off! It is possible that something is holding the 5v rail down (have you checked to see if any of the 8 DRAM chips (4164) get warm when it's...
by mikeb
Fri Feb 15, 2019 5:57 pm
Forum: General Discussion
Topic: Free ICs , CPLDs to good home !
Replies: 6
Views: 2355

Re: Free ICs , CPLDs to good home !

lezanderson wrote:
Fri Feb 15, 2019 12:33 pm
Anyone Building their own DIY ORIC / ATMOS ??
...
7805 5V Regulator
I wouldn't, if I were you ;) ...