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#a500

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hkz

Released the Rev 1 of my #Amiga500 "IDE activity LED injector" adapter.

It includes a small, optional improvement that uses 3 SMD components in addition to the rest, mainly a buffer for the IDE /ACTIVITY signal: I found that, with some of my SD card adapters, the signal was low enough when inactive (active low, remember) to leave the activity LED faintly lit.

If one doesn't care, a jumper can be bridged and the additional components left out.

github.com/hkzlab/A500_IDE_led

Photo of the underside of the board, with the SMD components soldered in
Photo of the upper side of the board, identical to the old revision
#A500
Public
Scott Small 🇨🇦

Spent the day visiting with the parents, and so Dad and I took another crack at repairing my #Amiga #A500.

This computer is _still_ kicking my ass, but we've gotten further than we did last time.

We've finally identified the issue with the keyboard. The fault is in the thin white connector that connects the PCB to the keyboard membrane - not the membrane itself (so I guess I didn't actually need to replace that...oh well). The /Y13, /Y9, and /Y8 signal lines will intermittently stop working, but wiggling the connector and putting pressure on it will make those lines work again.

(Except for the + key on the numpad. That one probably still has a bad switch.)

We tried cleaning the connector with Deoxit, but it didn't help any. So I decided to replace the controller PCB entirely with a DoohicKEY (retrosupplies.co.uk/amiga-ram-) - hopefully that will be the end of the keyboard problems for good. I'll update again once it arrives and is installed.

As for the serial port, we discovered a second broken trace which we quickly repaired, unfortunately it made no difference to the output of the diagnostic test. We followed the schematic and confirmed pins 2, 3, 4, 5, 6, 8, 20 all have continuity to the correct pins at U38/U39 (and pin 22 to R502), and that there aren't any shorts, so, not sure what's wrong here. Maybe a problem with the loopback adapter itself? That feels really unlikely though. Could also be a bad IC at U38 and/or U39? Or a CIA problem (maybe we should try swapping the CIAs?)

Truth be told, at this point I might put off the serial port problem until I actually have a need for the serial port (and another device to test it with).

The internal floppy drive also still isn't working, but we didn't have time to look at it today.

Previously: oldbytes.space/@smallsco/11381

Amiga Test Kit showing all keys on the keyboard working correctly, except for the + on the numeric keypad.
Amiga Test Kit performing a serial port diagnostic, showing errors on pins 2,3, and 5.
#RetroComputing
Public
Scott Small 🇨🇦

I thought I'd be bringing my #Amiga #A500 home today, but, this computer is kicking my ass 😅

The keyboard membrane has been replaced with a new PCB, and broken key plungers have ben replaced as well. The switches under the plungers have been cleaned with Deoxit, and the keys themselves have been given a good scrubbing with soap & water, plus a touch of Windex.

Unfortunately, many keys are still not working - not only that, it seems that my servicing has only made things worse. So I'm not sure where to go from here. Do I replace the IC on the keyboard controller next? Or maybe I need to start looking at traces on the motherboard?

Another possibility is that some of the key switches have just failed outright and there was never a membrane problem to begin with - and the switches need to be replaced entirely, not just the plungers.

What I really don't want to do is buy a whole new replacement keyboard, because that costs pretty much the same as what I paid for this computer to begin with.

Then there's the serial port. The original one had a number of bent, broken, and corroded pins - so (after much difficulty and with Dad's help) I removed it and replaced it with a new DB25 connector. We damaged one of the traces but fixed it with a bodge wire. The pins all have continuity, but something's clearly still wrong because the test kit is unhappy.

(I bought a DiagRom too, but forgot to buy the EPROM adapter, whoops! So that's now on the way as well to get a "second set of eyes" on the hardware)

There's also the floppy drive. It was working fine before we opened the machine up. It doesn't work any more. It spins up and makes noise like it's reading disks, but then drops back to the Kickstart boot screen. Now, we didn't clean or service the floppy drive because...it was working fine before (and I have a Gotek). But I'd like for it to still be working. Maybe some dust got in there or something?

Lastly there was the recap, which as far as I know was successful (unless that's what's causing the serial, floppy, and keyboard issues?) But one gotcha was that the two new 3300uf/25v caps are much larger than the old ones, and the RF shielding around the motherboard didn't fit any more. Eventually we managed to bend the caps over so that we could get the shield back on, but they still brushed against the shield and so we coated that part of the shield with electrician's tape to prevent them from coming into contact.

Ah, the joys of #RetroComputing repair 😂 at least the darn thing still boots!

A photograph of the Amiga Test Kit software running the serial loopback test, showing pins 2, 3, and 5 as bad.
A photo of the Amiga Test Kit software running the keyboard test, showing a number of failed keys: Left shift, 1, Q, A, Z, F4, 5, T, G, B, (, +, and .
Continued thread
Public
retrotechtive

Been doing some more on the #Amiga #A500 that I got up and running again.

First up, this is a rev 6 board with ECS but without 1MB Chip RAM enabled... so I enabled it.

Cut jumper J2 and solder the top pads together...

Then cut jumper JP7A (and don't solder anything).

This does mean you *have* to have the expansion RAM connected for the machine to work, but it gives 1MB chip RAM instead of half chip half slow memory.

JP2 has been cut, then soldered between the top two pads to enabled 1MB chip RAM.
JP7A is cut so that the machine no longer treats the expansion as and expansion - but instead as if it were on board RAM.
Continued thread
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retrotechtive

For anyone seeking to replace that line filter / choke on an #A500, the two things you need for a modern replacement are this:

digikey.ca/en/products/detail/

and the PCB:

pcbway.com/project/shareprojec

Don't worry that it's intended for the C64, it is the same functionally for the Amiga 500.

Solves a problem with an almost impossible-to-source old part. Especially useful for new #Amiga builds!

DigiKey ElectronicsCM4545Z131B-10 | DigiKey ElectronicsOrder today, ships today. CM4545Z131B-10 – 4 Line Common Mode Choke Through Hole 130 Ohms @ 100 MHz 10A DCR 10mOhm from Laird-Signal Integrity Products. Pricing and Availability on millions of electronic components from Digi-Key Electronics.
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