Search found 6550 matches

by 1024MAK
Wed Sep 20, 2017 10:07 pm
Forum: general
Topic: Today I received.....
Replies: 4136
Views: 215045

Re: Today I received.....

What! You've removed the fairy dust, you bad boy [-X

What will the pixies play with now?

Takes all the sparkle out. And on the lead-up to Christmas as well...

Mark
by 1024MAK
Wed Sep 20, 2017 4:44 pm
Forum: hardware
Topic: Challenge of the month - Troubleshooting?
Replies: 10
Views: 174

Re: Challenge of the month - Troubleshooting?

I have a project - photos later - that might, sort of, fit the bill. It's one of Mark Haysman's (RetroClinic) "I've now finished with this board" board :shock: Dave H :lol: p.s. I'll start a new thread when I have a few photos. p.p.s. this will be a loooooong project :D Do you need to bor...
by 1024MAK
Wed Sep 20, 2017 6:54 am
Forum: hardware
Topic: Challenge of the month - Troubleshooting?
Replies: 10
Views: 174

Re: Challenge of the month - Troubleshooting?

In my normal job, I'm a leader of a small team that maintains, fault finds and repairs electrical control systems. Hence in addition to tinkering with 1980s and 1990s computers and various other electronic and electrical items at home, I have a good understanding of investigating faults and failures...
by 1024MAK
Tue Sep 19, 2017 5:23 pm
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

@adrm good to hear that you have got it working :D Well done =D>

I thought a 74HC259 would work as a replacement, but had to point out the differences just in case it didn't :mrgreen:

Mark
by 1024MAK
Tue Sep 19, 2017 5:02 pm
Forum: general
Topic: Today I received.....
Replies: 4136
Views: 215045

Re: Today I received.....

:lol:

For £14.16 I could not resist...

See a review here :wink:

Most of my other meters are pictured here and there are close ups in a later post in this thread :D

I also have some analogue meters (sorry no photos yet) and at work I have an expensive Fluke meter.

Mark
by 1024MAK
Tue Sep 19, 2017 1:07 pm
Forum: general
Topic: Today I received.....
Replies: 4136
Views: 215045

Re: Today I received.....

So yesterday, two packets arrived. Thanks to Rob for the VideoNuLA board =D> The other item was a small and cheap multimeter from eBay:- IMG_5298.JPG IMG_5297.JPG IMG_5308.JPG IMG_5302.JPG IMG_5301.JPG IMG_5300.JPG IMG_5299.JPG It has the smallest cartridge fuses I have ever seen in a meter :shock: ...
by 1024MAK
Mon Sep 18, 2017 10:15 pm
Forum: other vintage computer hardware, software and games
Topic: Spectrum Currah MicroSource
Replies: 5
Views: 83

Re: Spectrum Currah MicroSource

Believe it or not, Currah actually made more expansions than just the microspeach. And they also made expansions for some other micros as well.

I can't remember if I have a copy of the ROM. I downloaded various ROMs from a web site a few years ago. If I have time, I'll see if I do have it.

Mark
by 1024MAK
Mon Sep 18, 2017 5:54 am
Forum: hardware
Topic: First ever BBC broken
Replies: 6
Views: 207

Re: First ever BBC broken

Well, at least you eventually fixed it :lol:

So well done on getting there in the end =D>

Mark
by 1024MAK
Sun Sep 17, 2017 9:36 pm
Forum: hardware
Topic: First ever BBC broken
Replies: 6
Views: 207

Re: First ever BBC broken

Yep, in order, things to check first are: ⋅ Power supply rails, which you have done. But have you checked the power pins of all the important chips? ⋅ The main clock circuits - as suggested above, check the clock output pins on the Videoproc / video ULA. Then check the clock on t...
by 1024MAK
Sat Sep 16, 2017 7:22 pm
Forum: hardware
Topic: Origins of the BBC keyboard layout
Replies: 5
Views: 197

Re: Origins of the BBC keyboard layout

More pictures of "dumb" terminals here.

Mark
by 1024MAK
Sat Sep 16, 2017 6:31 pm
Forum: hardware
Topic: Origins of the BBC keyboard layout
Replies: 5
Views: 197

Re: Origins of the BBC keyboard layout

A lot of the old computers took more hints on keyboard layouts from so called "dumb" terminal keyboard layouts than from other computers. But most of the old "dumb" terminals and their keyboards have disappeared into silicon heaven... And I expect that various people who went on ...
by 1024MAK
Sat Sep 16, 2017 5:41 pm
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

Argh, it was listed, but out of stock. What about the SN74HC259N vs the SN74LS259N? As I understand it, the HC is a direct replacement for LS, based on CMOS. No. 74HCxxx types are high speed CMOS versions and are not officially TTL compatible as they have different input switching thresholds (level...
by 1024MAK
Sat Sep 16, 2017 5:01 pm
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

Simple answer: "yes". Long answer, the part number 74LSXXX defines only the logic function and normally the pin-out. But not the actual circuitry used. In most applications, parts from different manufacturers (and sometimes from the same manufacturer) are equivalents and work okay. But in ...
by 1024MAK
Sat Sep 16, 2017 2:18 pm
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

RS also have trade counters, which come in very handy if you have one in your area.
Some other suppliers also have trade counters, but only a small number.

Mark
by 1024MAK
Sat Sep 16, 2017 10:30 am
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

I'm not at home, so can't check on my Beeb. However here are some details that may help. IC32 is a 74LS259 "high-speed" 8-Bit addressable latch used as a "port expander" to get more input/output pins. The schematic of the keyboard is here : http://mdfs.net/Info/Comp/BBC/Circuits/...
by 1024MAK
Sat Sep 16, 2017 8:40 am
Forum: for sale / freebies
Topic: VideoNuLA boards
Replies: 18
Views: 893

Re: VideoNuLA boards

Hi Rob

If you have some VideoNuLA boards left, and don't have any new first time customers interested, then I would like another one please.

Mark
by 1024MAK
Fri Sep 15, 2017 10:00 am
Forum: hardware
Topic: BBC Model B takes up smoking
Replies: 22
Views: 458

Re: BBC Model B takes up smoking

There are resistors (R2, R3 & R5) that will discharge the two 200V electrolytic capacitors (C6 & C8 ), but no separate discharge resistor for C1 and C2. However, they should discharge via R2, R3 & R5 if the bridge rectifier (DB1) is okay. Schematic of the primary side here :wink: It is a...
by 1024MAK
Fri Sep 15, 2017 7:48 am
Forum: for sale / freebies
Topic: Acorn Electron Bundle for Sale also BBC IO Relay Board and now Raspberry Pi
Replies: 10
Views: 369

Re: Acorn Electron Bundle for Sale and also Voltmace 14b Joystick

Bryce wrote:
1024MAK wrote: or screw thermal block...
Mark


I pretty sure you mean a screw terminal block... Unless it's getting hot? :D

Bryce.


:lol: That's another "correction" by the auto-suggest/auto-correct that I did not notice :lol:

Mark
by 1024MAK
Wed Sep 13, 2017 4:22 pm
Forum: software: new games
Topic: ZOMBIES ATE OUR ROADIES!
Replies: 28
Views: 592

Re: ZOMBIES ATE OUR ROADIES!

lurkio wrote:Or a PC with OmniFlop installed and working -- which is rarer, if anything.

Ha! I'll have to remember that if I sell a "retro" PC on fleabay... :lol:
by 1024MAK
Wed Sep 13, 2017 3:10 am
Forum: hardware
Topic: long beep and nothing else
Replies: 6
Views: 196

Re: long beep and nothing else

Given that it has recently worked, I suggest you check these first:- ⋅ Possible intermittent or poor connection of IC3 (6522 VIA) pins in it's socket. ⋅ You could also try swapping the 6522 for IC59 (the user port VIA) with IC3 (which is the system VIA). While there, also check f...
by 1024MAK
Tue Sep 12, 2017 7:30 pm
Forum: hardware
Topic: Desoldering components
Replies: 10
Views: 240

Re: Desoldering components

Part of this is the cost/benefit consideration. If you are regularly doing repair work, then the expensive gear is of benefit, as it speeds up the process of fault finding and fixing. But if you are only doing it occasionally, for double sided boards, just cut the pins of the suspect chip as near th...
by 1024MAK
Tue Sep 12, 2017 6:51 pm
Forum: hardware
Topic: New and interesting BBC fault
Replies: 14
Views: 360

Re: New and interesting BBC fault

Chip failure is often strange. Sometimes there is a reason that can be understood. But often failures appear to be random and unrelated to anything else.

I would'nt worry too much. The important thing is that it is now fixed and working :D

Mark
by 1024MAK
Tue Sep 12, 2017 3:11 pm
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

What was suggested was for the CPU address lines A0 to A15 to be connected to the logic analyser input channels 1 to 16. Then in the logic analyser software, set it to decode this as a hexadecimal number, then stop when it sees the selected address value. However, you would also need the phase 2 clo...
by 1024MAK
Tue Sep 12, 2017 2:20 pm
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

That's not looking like the problem then.

Mark
by 1024MAK
Tue Sep 12, 2017 2:13 pm
Forum: for sale / freebies
Topic: FS: Control Universal EuroBEEB
Replies: 7
Views: 171

Re: FS: Control Universal EuroBEEB

jonb wrote:OK Mark.

You know what condition it is in don't you? I think you advised me on the other threads... I'll PM you.

Yeah, akin to a banger of a car in a scrap yard... :lol:

Mark
by 1024MAK
Tue Sep 12, 2017 11:59 am
Forum: for sale / freebies
Topic: FS: Control Universal EuroBEEB
Replies: 7
Views: 171

Re: FS: Control Universal EuroBEEB

Oh boy, why not. Yes Jon, I'm interested.

Mark
by 1024MAK
Tue Sep 12, 2017 11:47 am
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

Early on in the start up code, a check is done to see if an external device wants to take control. It does this via the /IRQ line. At any time, a /NMI will cause a jump to the /NMI routine. /IRQ is level sensitive while /NMI is edge sensitive (triggers with a high to low pulse edge). /IRQ is on CPU ...
by 1024MAK
Tue Sep 12, 2017 11:31 am
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

Not sure if it's a relevant clue or not, but I just scoped the positive speaker pin on the MB to get a look at the wave generating the buzzing sound. According to my scope there's a 85 (-ish) KHz fluctuating signal coming from that pin. The audio circuits pick up all kinds of interference and noise...
by 1024MAK
Tue Sep 12, 2017 11:29 am
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

Check IC27 inputs and outputs, as shown in the following schematic diagram extracts:- Of course, the add in board may alter things a bit... Mark Pin 10 = permanently HIGH (As it should be?) PIN 9 = permanently LOW resulting in: PIN 8 = permanently HIGH But earlier you said One other thing, check wh...
by 1024MAK
Tue Sep 12, 2017 6:58 am
Forum: hardware
Topic: Troubleshooting my latest BBC B
Replies: 70
Views: 874

Re: Troubleshooting my latest BBC B

adrm wrote:NMI seems stuck low, no matter what. It fluctuates between -110mV and +380mV.
(Not sure if that +380mV peak I see constitutes a HIGH?)

Logic levels are supposed to be TTL, so a logic high is 2V to 5V.
Logic low should be between 0V and 0.8V inclusive.

More here :wink:

Mark

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