Search found 10861 matches

by 1024MAK
Tue Aug 03, 2021 7:20 pm
Forum: 8-bit acorn hardware
Topic: Is there any need to re-cap a second processor PSU?
Replies: 2
Views: 65

Re: Is there any need to re-cap a second processor PSU?

I’ve not done anything to my 6502 second processor. Keep in mind that the PSU in the 6502 second processor is a traditional type. It uses a mains frequency transformer and a series pass regulator system. It does not have any of the Rifa capacitors (they are the ones that smoke in a BBC Micro PSU). S...
by 1024MAK
Sun Aug 01, 2021 1:01 pm
Forum: 8-bit acorn software: other
Topic: Why was BBC BASIC so fast?
Replies: 233
Views: 16076

Re: Why was BBC BASIC so fast?

Richard has a point that is worthwhile expanding a little. Until systems started loading the BASIC interpreter from a disk file into RAM, and the available RAM was reasonably large (for a home computer), all the BASIC interpreters for home computers were limited in the available size of the ROM chip...
by 1024MAK
Sat Jul 31, 2021 3:27 pm
Forum: 8-bit acorn hardware
Topic: Electron Screen dodgy when warm
Replies: 20
Views: 498

Re: Electron Screen dodgy when warm

Okay, so the program runs fine. That means the digital circuitry is okay. You said you can get a colour picture using the RF/UHF TV out. That tells me that most of the video circuitry is working okay. LK4 is not fitted, so the composite video output should be monochrome. But you are getting colour p...
by 1024MAK
Wed Jul 28, 2021 9:27 pm
Forum: 8-bit acorn hardware
Topic: Electron Screen dodgy when warm
Replies: 20
Views: 498

Re: Electron Screen dodgy when warm

If you disable the colour output on the composite video output by removing jumper shunt/link LK4, is the picture more stable (it will be grey scale or black white depending on what ‘colours’ are being shown). LK4 does not have a jumper on my board It may be a wire link. If so you can cut it. If you...
by 1024MAK
Wed Jul 28, 2021 12:29 pm
Forum: 8-bit acorn hardware
Topic: Electron Screen dodgy when warm
Replies: 20
Views: 498

Re: Electron Screen dodgy when warm

If you disable the colour output on the composite video output by removing jumper shunt/link LK4, is the picture more stable (it will be grey scale or black white depending on what ‘colours’ are being shown).

Mark
by 1024MAK
Wed Jul 28, 2021 12:02 pm
Forum: 8-bit acorn hardware
Topic: Electron Screen dodgy when warm
Replies: 20
Views: 498

Re: Electron Screen dodgy when warm

dominicbeesley wrote:
Wed Jul 28, 2021 10:42 am
Are you connecting via uhf or composite? It might just be going out of tune. You could try an rgb to scart cable
He replied earlier saying composite video.

Mark
by 1024MAK
Tue Jul 27, 2021 8:48 pm
Forum: 8-bit acorn hardware
Topic: Electron Screen dodgy when warm
Replies: 20
Views: 498

Re: Electron Screen dodgy when warm

So the first thing to do, assuming you have not already done it, is to measure the +5V and the -5V supplies on the main board. Where the wires come from the PSU board is fine. Are they within specification (+5V should be between 4.75V and 5.25V, the -5V is less critical)? If they are okay, now probe...
by 1024MAK
Tue Jul 27, 2021 7:20 pm
Forum: 8-bit acorn hardware
Topic: Electron Screen dodgy when warm
Replies: 20
Views: 498

Re: Electron Screen dodgy when warm

citizenfish wrote:
Tue Jul 27, 2021 4:30 pm
Sadly a remove, clean and replace has not fixed the problem. The ULA seating pins look ok as does the base of the ULA
What test gear do you have or have access to?

Mark
by 1024MAK
Mon Jul 26, 2021 4:12 pm
Forum: 8-bit acorn hardware
Topic: Electron Screen dodgy when warm
Replies: 20
Views: 498

Re: Electron Screen dodgy when warm

Electrons don’t normally need recapping… In fact, capacitor failure is relatively rare.
The most common problem is poor electrical contacts between the ULA and its socket.

How are you connecting to your display?

Mark
by 1024MAK
Sun Jul 25, 2021 12:12 pm
Forum: 8-bit acorn hardware
Topic: Faulty BBC
Replies: 7
Views: 216

Re: Faulty BBC

DRAM often can retain data for longer than the specification timings given in data sheets (as Sinclair discovered with a design error in the refresh circuitry for the ‘lower’ 16k DRAM in the ZX Spectrum). But if the time interval is too long, when next read, the DRAM will return garbage. Also the ti...
by 1024MAK
Sun Jul 25, 2021 10:24 am
Forum: 8-bit acorn hardware
Topic: Faulty BBC
Replies: 7
Views: 216

Re: Faulty BBC

Do you really mean IC2, the 6845 CRTC?

As without this you will not get a video picture and the RAM will not be properly refreshed.

Mark
by 1024MAK
Sat Jul 24, 2021 9:20 pm
Forum: 8-bit acorn hardware
Topic: Electron ULA Documentation Updates
Replies: 72
Views: 12820

Re: Electron ULA Documentation Updates

Acorn Electron Advanced User Guide
jms2 wrote:
Sun Apr 30, 2017 8:32 pm
OK - here's Draft 2 of Issue 3 of the Electron Advanced User Guide.
Budgie wrote:
Wed Jan 27, 2021 9:41 pm
Just curious as to whether a "final" document has been produced yet just in case I ever want to get a copy printed ?

Thanks

Andy
Bump! :mrgreen:

Mark
by 1024MAK
Fri Jul 23, 2021 8:20 pm
Forum: 8-bit acorn hardware
Topic: Beeb: Intermittent Keyboard Fault
Replies: 3
Views: 106

Re: Beeb: Intermittent Keyboard Fault

The BREAK key is not part of the keyboard matrix, it’s completely independent. The two SHIFT keys and the CONTROL key are connected slightly differently to the rest of the keys. All remaining keys are part of the (normal) keyboard matrix. Have you tried each key? Including the number keys, symbol ke...
by 1024MAK
Fri Jul 23, 2021 5:34 pm
Forum: 8-bit acorn hardware
Topic: 14-inch monitor in unknown condition - worth the risk of plugging it in?
Replies: 6
Views: 193

Re: 14-inch monitor in unknown condition - worth the risk of plugging it in?

It depends on what you mean by tripping… The only way to prevent a faulty item from tripping a RCD or RCBO is to use a isolation transformer. But these are large and heavy, and not cheap… For a fuse board, normally the fuse in the 13A plug will blow first (as long as it’s actually a proper legitimat...
by 1024MAK
Mon Jul 19, 2021 10:21 pm
Forum: 8-bit acorn hardware
Topic: Plus3 problem
Replies: 22
Views: 603

Re: Plus3 problem

Definitely worth changing IC3. But before you do, forgive me, but I have to ask the obvious question, have you cleaned the edge-connector contacts and check the edge-connector female sockets for bent or misshapen contacts?

Mark
by 1024MAK
Sun Jul 18, 2021 11:00 am
Forum: 8-bit acorn hardware
Topic: Most common BBC IC failures?
Replies: 7
Views: 286

Re: Most common BBC IC failures?

IC14 (74LS245) is worked hard, and it is one of the critical components. Hence it is a ‘stock fault’. And occasionally the 6522 system VIA or user VIA fail. Hence the common advice to remove the system VIA (IC3), put it to one side, then swap the user VIA (IC69) over to replace IC3. But the most com...
by 1024MAK
Sun Jul 18, 2021 10:39 am
Forum: 8-bit acorn hardware
Topic: Dead Elk, repairs ongoing
Replies: 66
Views: 1369

Re: Dead Elk, repairs ongoing

The only way to try to win when against a sniper (auto bidding software) is to also use a sniper system and to give it the range to put in a silly high bid… Then hope that your maximum is higher than the maximum of the other sniper…

Mark
by 1024MAK
Sun Jul 18, 2021 10:09 am
Forum: 8-bit acorn hardware
Topic: RAMAMP ROM6S expansion board and strange ROM?
Replies: 4
Views: 214

Re: RAMAMP ROM6S expansion board and strange ROM?

The signal at IC77 pin 8 is suitable for the /WR input on peripheral chips that are designed to work with Z80/8080/8085 processors. Or where the circuitry needs the phi2 signal to be gated in to the read/write signal.

Mark
by 1024MAK
Fri Jul 16, 2021 11:30 pm
Forum: 8-bit acorn hardware
Topic: Renovating a partly upgraded Model A
Replies: 37
Views: 969

Re: Renovating a partly upgraded Model A

More likely it’s due to the Beebs master 16MHz clock and the way that Acorn derived the clock for the Teletext chip (IC5). But I thought Ian & Dave's RGB2HDMI adapter specifically worked around that timing hack to produce stable output on Mode7? The RGB2HDMI adapter tries to. Hence why there ar...
by 1024MAK
Fri Jul 16, 2021 11:22 pm
Forum: 8-bit acorn hardware
Topic: Renovating a partly upgraded Model A
Replies: 37
Views: 969

Re: Renovating a partly upgraded Model A

More likely it’s due to the Beebs master 16MHz clock and the way that Acorn derived the clock for the Teletext chip (IC5).
Somewhere in this topic, there are more details. But you may want to search for ‘asymmetric’

Mark
by 1024MAK
Fri Jul 16, 2021 10:19 pm
Forum: 8-bit acorn hardware
Topic: Renovating a partly upgraded Model A
Replies: 37
Views: 969

Re: Renovating a partly upgraded Model A

…but at 30 mins in, the "new" VideoProc is already very warm. I do wonder if some heatsinks and a small fan might not be a wise idea in the long term... The VTi versions don’t need heatsinks. Silicon chips have an operating temperature much higher than people expect. The internal maximum ...
by 1024MAK
Fri Jul 16, 2021 10:06 pm
Forum: general
Topic: Anti unravel plastic
Replies: 6
Views: 293

Re: Anti unravel plastic

there are purpose designed tapes, e.g. this type that should last even longer. Ooo I thought £5.29 not bad, whats the £9.95 handling charge :-& I did ponder clear wide heatshrink, I will have to play around with stuff. It would be nice to see all the colours. Ashley. In common with suppliers th...
by 1024MAK
Fri Jul 16, 2021 1:20 pm
Forum: general
Topic: Anti unravel plastic
Replies: 6
Views: 293

Re: Anti unravel plastic

Good quality insulation tape would be better than sellotape. But cheap stuff may over time suffer from the same problem as sellotape. The adhesive in some good types does last a long time.
However, there are purpose designed tapes, e.g. this type that should last even longer.

Mark
by 1024MAK
Fri Jul 16, 2021 12:32 pm
Forum: 8-bit acorn hardware
Topic: Strange BBC Micro Issue 3 motherboard addition
Replies: 8
Views: 433

Re: Strange BBC Micro Issue 3 motherboard addition

C42 is part of the ‘clean-up’ circuitry for the 16MHz clock signal. So maybe this was an owner or service technician trying to get a cleaner clock to improve the timings. Either for a better video output or some other reason.

Mark
by 1024MAK
Fri Jul 16, 2021 11:23 am
Forum: 8-bit acorn hardware
Topic: Troubleshoot loading cassette tapes
Replies: 54
Views: 1315

Re: Troubleshoot loading cassette tapes

The forum software compresses all picture or photo images that are attached in the normal way.

Hence if detail is important, images should be put in a container format to preserve the detail.

Mark
by 1024MAK
Fri Jul 16, 2021 11:18 am
Forum: 8-bit acorn hardware
Topic: Renovating a partly upgraded Model A
Replies: 37
Views: 969

Re: Renovating a partly upgraded Model A

Kynar wire is type of wire that is what is normally recommended. This resists ‘melt back’. I often use solid core PVC insulated 0.63mm dia wire, as I have lots of off-cuts of it. But being PVC insulated, the insulation will melt back if it gets too hot. Enamelled wire can be used, but the thickness...
by 1024MAK
Thu Jul 15, 2021 3:06 pm
Forum: 8-bit acorn hardware
Topic: Industrial use of 8bit kit
Replies: 27
Views: 742

Re: Industrial use of 8bit kit

Some parts of the mainland U.K. railways used BBC Micros to provide the customer information screens showing train arrivals, departures and other train information. And of course, the BBC used Beebs for all sorts of things in and around TV program production. More information on both these is elsewh...
by 1024MAK
Thu Jul 15, 2021 2:58 pm
Forum: 8-bit acorn hardware
Topic: Renovating a partly upgraded Model A
Replies: 37
Views: 969

Re: Renovating a partly upgraded Model A

Insulation that can withstand being pressed against the bottom of the PCB is a must!

I’m not sure I would be happy with unprotected enamelled wire…

Mark
by 1024MAK
Thu Jul 15, 2021 8:00 am
Forum: 8-bit acorn hardware
Topic: Troubleshoot loading cassette tapes
Replies: 54
Views: 1315

Re: Troubleshoot loading cassette tapes

With the iron set to a higher temperature, the Warton 1.0mm 63/37 solder should work fine.
A quick search only found this U.K. supplier (link) excluding eBay. So I searched a bit more, and found that CPC stocks various Warton products (link). So it should be good solder.

Mark
by 1024MAK
Thu Jul 15, 2021 7:45 am
Forum: 8-bit acorn hardware
Topic: Renovating a partly upgraded Model A
Replies: 37
Views: 969

Re: Renovating a partly upgraded Model A

As far as I know, it will not cause any problems. I suggest you use a different mode (just like Electron users do :mrgreen: ). If you are careful, you can use some thin solid core copper PVC insulated wire 0.63mm dia to 0.9mm dia like fixed telephone or fixed network cable. Keep in mind that the PVC...

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