Search found 8376 matches

by 1024MAK
Wed Mar 20, 2019 3:16 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 3
Views: 39

Re: Mystery Zener Diode

No you can’t leave it out. It looks like it is part of the snubbing network. If you don’t replace it, sooner or later something else may fry. And that assumes that leaving it out has no operational affect... At a guess, assuming it is actually a Zener, the voltage is likely to be greater than the su...
by 1024MAK
Wed Mar 20, 2019 11:53 am
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 26
Views: 560

Re: Megastor 8" drive unit

If the transistor has been damaged internally, there is likely to be a short circuit between the base and the emitter or collector...

Mark
by 1024MAK
Tue Mar 19, 2019 6:35 pm
Forum: other vintage computer hardware, software and games
Topic: 6847 question.....
Replies: 1
Views: 66

Re: 6847 question.....

The function of TR2 is to increase the output current and reduce the output impedance. There is no voltage gain in this configuration. Using the (collector) output of TR1 may work, but it very much depends on the circuit it is driving. If the input impedance of the circuit that it is driving is high...
by 1024MAK
Tue Mar 19, 2019 1:14 pm
Forum: hardware
Topic: Battery backup !!!
Replies: 6
Views: 175

Re: Battery backup !!!

But I think we can safely say that zinc batteries aren't "leak proof" :D No battery technology that uses a liquid electrolyte is 100% leakproof unless the electrolyte is a thick gel. If you want the assurance of a battery technology that is the least likely to leak, go for a 3V lithium cell. But do...
by 1024MAK
Mon Mar 18, 2019 10:51 pm
Forum: hardware
Topic: Battery backup !!!
Replies: 6
Views: 175

Re: Battery backup !!!

Well, as in everything in life, a number of factors come into play. There are three main reasons why consumer cells / batteries leak. First, abuse. If a cell or battery is short circuited or overcharged, the internal pressure rise will cause a vent hole to open. This is a special area of the case th...
by 1024MAK
Mon Mar 18, 2019 2:16 pm
Forum: hardware
Topic: Storing & Protecting hardware
Replies: 6
Views: 200

Re: Storing & Protecting hardware

Yes, ANY cell(s) or battery should be removed before storage.

Any leakage can find its way around inside the computer and get to places you would not imagine. Gravity will only pull it down if the droplets are big enough that gravity wins over surface tension.

Mark
by 1024MAK
Sun Mar 17, 2019 5:25 pm
Forum: hardware
Topic: Storing & Protecting hardware
Replies: 6
Views: 200

Re: Storing & Protecting hardware

There are five things you need to protect against: Physical damage Extremes of hot and cold Damp / condensation / water UV light PVC plasticiser migration The first can either be strong double or triple layer cardboard boxes. If you can find one box that nicely fits inside another, that's a good sta...
by 1024MAK
Sun Mar 17, 2019 2:13 pm
Forum: hardware
Topic: BBC B+ 128K: Fault after warming up.
Replies: 19
Views: 619

Re: BBC B+ 128K: Fault after warming up.

BBC B+ main RAM IC49 (74LS245) transceiver connects the DRAM and the CPU (IC42). Which direction (read/write) depends on the R/W signal on pin 1 and enable /G being low (pin 19). IC54 (74LS273) copies (reads) the data from the DRAM to the teletext chip IC59, SAA5050). The videoproc IC53 also reads ...
by 1024MAK
Sun Mar 17, 2019 1:49 pm
Forum: hardware
Topic: BBC B+ 128K: Fault after warming up.
Replies: 19
Views: 619

Re: BBC B+ 128K: Fault after warming up.

Write data to the DRAM only comes from the CPU. The DRAMs (and other RAM, ROM/EPROM and IO devices) provide read data to the CPU and to the video system (videoproc/teletext chip). When neither a read or a write is being performed, the data bus is undriven, so any voltage left on the data lines due t...
by 1024MAK
Sat Mar 16, 2019 8:09 am
Forum: community projects
Topic: Earliest examples of each machine?
Replies: 41
Views: 5632

Re: Earliest examples of each machine?

Looks like it has been stored somewhere damp, looking at the cassette, RGB, composite video and Modulator connectors on the side.
555BBE4C-D164-4781-99AD-285FE43B8CFA.jpeg
07-ALA01-000333 Electron
9EC349B0-312F-44EE-A41A-4039EB516160.jpeg
07-ALA01-000333 Electron
Mark
by 1024MAK
Sat Mar 16, 2019 7:52 am
Forum: hardware
Topic: Putting together a GOTEK, what do I need...
Replies: 17
Views: 419

Re: Putting together a GOTEK, what do I need...

A lot of the bits, such as pin headers, DuPont cables, ribbon cable etc. are available from the smaller, hobby friendly electronics suppliers such as ESR.

See also this thread which lists various suppliers.

Mark
by 1024MAK
Fri Mar 15, 2019 9:43 pm
Forum: acorn atom and system
Topic: Atom 2k18 ?
Replies: 159
Views: 4576

Re: Atom 2k18 ?

roland wrote:
Fri Mar 15, 2019 8:30 pm
I also added a bunch of capacitors that go the the + and - of the IC's (I don't know the exact English words for it but the description will do, at least I hope so).
Do you mean decoupling capacitors?

Mark
by 1024MAK
Fri Mar 15, 2019 1:00 pm
Forum: hardware
Topic: A potential run of BeebSCSI 7.7 (the newest)
Replies: 41
Views: 1013

Re: A potential run of BeebSCSI 7.7 (the newest)

It’s looking like the second run may need to be 20 units :shock:

Mark
by 1024MAK
Fri Mar 15, 2019 12:44 pm
Forum: hardware
Topic: My electron doesn't look well...
Replies: 11
Views: 249

Re: My electron doesn't look well...

It’s now play time... :D

Have fun :lol:

Mark
by 1024MAK
Fri Mar 15, 2019 12:00 pm
Forum: for sale / freebies
Topic: B diagnostics/Tube USB serial adapter (FT232H)
Replies: 11
Views: 1149

Re: B diagnostics/Tube USB serial adapter (FT232H)

EdVoncken wrote:
Fri Mar 15, 2019 11:47 am
Not sure if I can send PMs yet.
You can ask for PMs to be enabled by using the Contact us link (envelope icon) at the bottom of every page. This notifies the admin’s.

Mark
by 1024MAK
Fri Mar 15, 2019 11:55 am
Forum: hardware
Topic: I2C 4 U
Replies: 372
Views: 22747

Re: I2C 4 U

In my designs, I always provide provision for a 100nF multilayer ceramic capacitor as close as possible to the output and ground/0V pins of a voltage regulator chip. This would be in parallel with the electrolytic capacitor. As Martin says, also include a 470nF multilayer ceramic capacitor near the ...
by 1024MAK
Fri Mar 15, 2019 7:24 am
Forum: hardware
Topic: Beeb Power Supply Issue
Replies: 7
Views: 248

Re: Beeb Power Supply Issue

Also note that the big power transistor has three electrical connections. Two are via PCB pins, the third is via the two mounting machine screws. Make sure that these are providing a good reliable connection.

Mark
by 1024MAK
Thu Mar 14, 2019 2:37 pm
Forum: community projects
Topic: Merging scans
Replies: 3
Views: 85

Re: Merging scans

I use GIMP on my Linux system for spicing/joining and editing picture/photo/scan files. GIMP is primarily a photo editing application. I normally cut images into manageable chunks, carefully selecting the edges to be where there are vertical and horizontal easily identifiable features, and overlappi...
by 1024MAK
Thu Mar 14, 2019 12:27 pm
Forum: for sale / freebies
Topic: Electron MicroSD Card Interfaces (now Mk2)
Replies: 85
Views: 2407

Re: Electron MicroSD Card Interfaces

For any new / recent members, who can’t send Private Messages (PMs):

You can ask for PMs to be enabled by using the Contact us link (envelope icon) at the bottom of every page. This notifies the admin’s.

Mark
by 1024MAK
Thu Mar 14, 2019 10:22 am
Forum: hardware
Topic: Beeb Power Supply Issue
Replies: 7
Views: 248

Re: Beeb Power Supply Issue

The most common areas where dry joints form are on transformer pins, high power resistor legs and power transistor connections. If a joint looks suspicious, don’t just heat it up and put fresh solder on it. Desolder the joint and look for any contamination. Clean both the pad and the leg/terminal th...
by 1024MAK
Wed Mar 13, 2019 6:54 pm
Forum: general
Topic: Today I received.....
Replies: 5058
Views: 369658

Re: Today I received.....

rmbrowngr wrote:
Wed Mar 13, 2019 6:44 pm
danielj wrote:
Wed Mar 13, 2019 6:37 pm
It is indeed a B+ - I'd recommend a multios in there so you can run it in beeb-mode too :)

d.
Good recommendation. Thanks. A trip to RetroClinic needed.

Any other recommendations?
Confused :?

A BBC B+ is a Beeb not a Master...

Mark
by 1024MAK
Wed Mar 13, 2019 5:02 pm
Forum: hardware
Topic: Master audio noise
Replies: 13
Views: 196

Re: Master audio noise

I presume the third Tantalum capacitor is C14, which is a 4.7uF type. Again, replace it with a new Tantalum rated at 25V or a electrolytic rated at 16V.

If you are not using the internal speaker, IC13, the LM386 is not doing anything useful.

Mark
by 1024MAK
Wed Mar 13, 2019 4:56 pm
Forum: hardware
Topic: Master audio noise
Replies: 13
Views: 196

Re: Master audio noise

I would replace both C15 and C17 on the main Master 128 board. Both are used for smoothing and filtering the +5V and -5V power rails that feed the analogue audio circuitry. Replace with either 10uF or 22uF Tantalum capacitors rated at 25V or greater. Or with electrolytic types, again 10uF or 22uF, r...
by 1024MAK
Wed Mar 13, 2019 4:33 pm
Forum: hardware
Topic: Fitting external upgrades internally
Replies: 5
Views: 200

Re: Fitting external upgrades internally

Zaxon does a ‘micro Gotek’, see this page on Sell My Retro.

Mark
by 1024MAK
Tue Mar 12, 2019 3:32 pm
Forum: general
Topic: Today I received.....
Replies: 5058
Views: 369658

Re: Today I received.....

Ahh, Rumbelows, back when shops gave you a handwritten receipt. Brings back memories of 1983....

Mark
by 1024MAK
Tue Mar 12, 2019 3:30 pm
Forum: general
Topic: Today I received.....
Replies: 5058
Views: 369658

Re: Today I received.....

Is there a guide somewhere for how to recap/futureproof an Electron?? No, because there are no capacitors that need renewing normally. The internal Elk PSU is normally very reliable. The external PSU (which is just a transformer in a plastic case) suffers from the low voltage cable suffering breaks...
by 1024MAK
Tue Mar 12, 2019 3:00 pm
Forum: hardware
Topic: Cumana CS400 switchable drive - noises and disk errors
Replies: 29
Views: 878

Re: Cumana CS400 switchable drive - noises and disk errors

As TD62503 chips are open collector transistor arrays, I would expect any load, such as a solenoid to have one wire/terminal connected to a positive power rail (+5 V or +12V) and the other wire/terminal to be connected to one (or two) of the chips output pins. Datasheet here :wink: Oh, and be carefu...
by 1024MAK
Tue Mar 12, 2019 10:30 am
Forum: hardware
Topic: My Master internal pics
Replies: 15
Views: 258

Re: My Master internal pics

Oh and AA alkaline cells last about one to two years, then need replacing. Don’t go for the likes of Duracell. My workplace uses them and they often leak. I don’t buy any Duracell cells or batteries because of this.

Mark
by 1024MAK
Tue Mar 12, 2019 10:23 am
Forum: hardware
Topic: My Master internal pics
Replies: 15
Views: 258

Re: My Master internal pics

Many thanks. Retro clinics set is cheap enough so will grab that. IIRC (been a while since I was in a Master PSU) the PSU for one of the X2 capacitors has holes for two different component pitches. So I suggest you tell Mark (RetroClinic) that you want the capacitors for a Master 128. The resistor ...
by 1024MAK
Tue Mar 12, 2019 10:08 am
Forum: acorn atom and system
Topic: Atom 2k18 ?
Replies: 159
Views: 4576

Re: Atom 2k18 ?

For slow 1MHz I/O devices, if there were enough FPGA pins, I would suggest a separate “slow” bus. Writes to a slow bus device could be latched in a buffer and it’s outputs held until the external device had had enough time to capture the data. Alternatively a CPLD could be used to do the same thing ...