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56 votes
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Zilog Z80 freezes while binary counting up to 65 536 (2^16)

There are many issues here. As it is already said in comments, decoupling capacitor is a must! 555 (non-CMOS) timer output is very much like the output of TTL ICs, however Z80 requires a firm logic ...
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  • 9,376
19 votes

I've taken my Amiga computer out of storage after several years and it doesn't work. What's the likely cause?

First of all you should remove all unnecessary peripherals and cables from the Amiga, in case it is a faulty device that is preventing it from working. All you need is the power cable, display cable, ...
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14 votes

Zilog Z80 freezes while binary counting up to 65 536 (2^16)

I'd just like to expand on a couple of points in lvd's excellent answer. Reset Circuit You might get by with just using a jumper wire to short the reset pin to ground for a brief moment after you've ...
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13 votes

Can polarity inversion damage a ZX Spectrum?

You have damaged your Spectrum for sure. The first casualty is the 7805 regulator. These normally explode and release a "black smoke of the death" clearly visible, but yours doesn't seem to be the ...
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12 votes
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What's a safe and easy way to desolder the CPU from C64?

The easiest way to desolder a dead chip is to cut the legs with your snips then remove each pin one at a time. Use a solder pump or solder braid to clean the holes. I would use an IC socket when ...
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11 votes

How do I troubleshoot an Apple //e with no power light?

Some of your general questions can be answered here. As I said above, for an Apple //e remove all cards for troubleshooting - none are necessary for boot-up in a typical system. (As opposed to an ...
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11 votes

C128D shorted Composite and Ground

Whatever would have taken place occurred inside the RF modulator: I haven't been able to find a C128 schematic that includes the modulator, however if it's anything like the C64 modulator, there's a ...
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9 votes
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Is it possible to bend tension back into Atari 2600 joystick contact domes?

TLDR; Yes you can bend them, don't bend them too much and don't flatten the dimples. First be sure the contact disk is the issue. If the problem is intermittent, You can also remove power from the ...
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9 votes

Replacing the floppy drives in my Amiga 3000

Here and here are lists of drives that work on Amigas either natively or that can be electrically modified to work on Amigas. Some of the drives are still in production. Those vendors you found ...
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9 votes
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Why does my IBM 5154 have an undulating wave?

It was because I forgot to plug a jumper into a socket that switches it from a 240V AC input to 120V AC input (socket M5). I simply forgot to plug it in. That's not the ONLY thing I did wrong, but it'...
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9 votes
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CBM PET 2001 garbled screen

The garbled screen is normal on startup, but should be replaced by the BASIC screen after a moment. There's a rather detailed troubleshooting guide, including links, at http://www.dasarodesigns.com/...
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  • 7,854
9 votes

C128D shorted Composite and Ground

The C128D modulator uses 5V for power supply, and the composite output (pin 4) is driven with luma signal via an emitter follower and a 120 ohm resistor, and with chroma signal via an emitter follower ...
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8 votes
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What cleaning/repair can be done to a Mega Drive cartridge slot?

Have you tried cleaning the pin connector inside the Mega Drive? It's fairly simple to remove the shell and access the pin connectors. (don't forget to remove the LED wires for model 1) I got a second ...
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  • 919
8 votes

Used PS1 "slim" (PSone) freezes on boot

I bet you have a dirty lens or faulty optical drive. Try cleaning the diode with a Q-Tip and a electronic lens cleaning solution. It's also possible that the entire drive is broken or dirty. Does ...
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  • 9,242
8 votes
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Finding replacement LEDs for Commodore gear?

(This question is a bit close to 'what to buy', but examples given are just such, as there are other suppliers) These are not wide ones, but two within one package. Looking at the back will show that ...
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  • 174k
8 votes

Modern heat sinks for Commodore C64/C128

Modern heat sinks I assume this is about heat spreaders, as that is what they do. What is a reliable modern replacement Any one available at the usual stores will do it Which chips in the C64 and ...
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  • 174k
7 votes
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Installing hdd on PhoenixBIOS A486 on Gateway 2000 4DX-33

When the battery died and reset the system, could this have reverted the BIOS to an earlier version that did not support the hard drive? No. BIOS is a motherboard firmware program which is usually ...
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  • 186
7 votes

Replacing Amiga 9 pin D-Sub mouse cable

Unfortunately there were a few "revisions" of the mouse, and the pads on the mouse side were not always signed; the color coding isn't guaranteed to be repeatable either. If your mouse has the pins ...
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  • 6,645
7 votes

What's a safe and easy way to desolder the CPU from C64?

For destructive desoldering @Tim Rings method is usually the fastest: clip all pins, remove the chip and desolder each pin separately. Just be careful when clipping the pins. Use a small tool and try ...
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  • 174k
7 votes

Is is possible to repair a SE/30 with reversed C2 and C11 capacitors?

The schematics for the SE/30 can easily be found on internet, for example here This is what I can see on the main circuit board. A quick glance tells that C2 is connected between ground and +12 V ...
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  • 1,707
7 votes

Preventing socketed chip corrosion?

Low humidity helps, but beyond that there are no good solutions. You can coat the exposed parts with a protective seal but then they become difficult to maintain. Preventative maintenance is an ...
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  • 14k
7 votes
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Preventing socketed chip corrosion?

As already stated, there is no solution. I am a collector/restorer of stand up video arcade machines and pinball machines, and these all suffer from corrosion. Even after I have cleaned and restore a ...
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  • 531
7 votes

Modern heat sinks for Commodore C64/C128

An unmodified machine includes a large metal RF shield which usually performs the duty of being a heat sink for VIC-II, SID, and other chips. I've worked on dozens of C64s, and have only seen the ...
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7 votes

Macintosh Plus always resets on power up

My guess is transient undervoltages on the +12V rail. I'm basing this on both the floppy drive (schematic top-right, G4) and the flyback circuitry (figure 2) drawing power from that rail. If you ...
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  • 8,930
7 votes
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Is this SpeedDOS chip mounted right in my C64?

In general, IC orientation is designated by the notch in the centre on one end of the IC. (Don't make assumptions based on the text direction, although typically it will flow left to right from the ...
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  • 4,348
6 votes

Repairing/Lubing/Fixing Amiga 500 floppy drive

It is possible that the old lubrication on the sticking part has absorbed some fluff or grit and so is no longer working as a lubricant. The build-up of muck could be around the point where the arm ...
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  • 7,609
6 votes
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How to fix Apricot Xi keyboard

When I patched up my Xi keyboard, I used double-sided adhesive pads cut to the right size, with aluminium foil tape to replace any missing discs. These days it's also possible to buy replacement foam ...
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  • 5,882
6 votes

Will this Acculite laptop boot without HDD?

AFAIK, BIOS has always allowed booting from floppy. I can't imagine why any manufacturer would override that possibility. IIRC, the default boot order in the 386 era was A, B, and then C. Some BIOSs ...
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  • 8,196
6 votes

How to renew and re-ink old printer ribbons?

I don't know if this is the "best" solution, but I have found applying Singer light sewing machine oil to a dried-out fabric printer ribbon appears to be effective. This oil is odorless. Amazon: ...
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  • 3,491
5 votes

How to renew and re-ink old printer ribbons?

In the old days(tm) it was common to reink fabric ribbons for typewriters, in fact, the early ones where made that way. I kept using that practice during the 70s and 80s for daisy wheel and dot matrix ...
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