Ketchup

Yeah, it’s been a while.

TI 99/4a

A quick update on the TIPI/32k. It’s now in a case I made from an old Jiffybox, that was almost exactly the right size. I just plumbed in some cuts and some drill holes and it’s now no longer just a bare PCB.

Amiga Sidecar

A friend asked me to have a look at his Amiga Sidecar, that apparently had electrocuted him. This is not normal behaviour. I specifically said I couldn’t look at the Sidecar itself, but was happy to look at the rest of it. The previous owner had

done some interesting mods to it, including routing the floppy drive connection out the back, then routing the floppy drive back inside, leaving a hole at the back.

The main thing my friend wanted was the side mounted power switch working. That , and less electrocution.

Looking inside, I could see that the pins used to connect the mains to the mains PCB had come loose. This was most likely what caused all the sparky stuff.

On the underside, things got worse…

When it cut loose, it sooted up nearby components.

(That’s the heatsink next to the power connectors. You can just make out the pins in the foreground)

Something literally exploded off and bounced across the insulation board underneath.

First thing I did was test the fuse. It hadn’t blown. It should have so I replaced it.

I toned out the traces on the underside. One had completely exploded off the board. I resoldered the connector pins in place, and built up the contacts to give them more current capacity. For the exploded one, I bent a piece of wire up as a replacement track, then flooded it with solder to make sure it could carry the current and not crack. I sealed the whole lot, once finished, with nail polish.

I checked the on off switch. It was very janky, tending to lock in an “on” position. Never a good thing, so I sourced the closest switch I could source locally and replaced it. I had to widen the switch hole slightly, but it was a good match.

(The original switch. Even disassembling it and cleaning it didn’t help).

Finally all the connectors that didn’t have hoods on the connectors got shrink-wrapped to make sure there was less chance of issues.

Carefully turning it on, with everything unplugged, it didn’t explode, and I could see sane voltages from the various rails, so that was good. PLugging it all back together, I got drive activity, but without an Amiga, there wasn’t much more I could do. (Later testing showed no life, so there is more work to do on that system)

I have returned it to the original owner.

Oric Atmos

I swapped a TIPI/32k for an Oric Atmos, a lovely little 6502 based system that was originally designed to be a competitor to the Sinclair Spectrum. It was in rough state, but considering how much Orics sell for, I wasn’t complaining.

It used a 9V center positive PSU, so I grabbed one of my adjustable PSUs and plugged it in. Turning it on and tuning in the TV, I got the following display.

Well, it’s doing something.

I popped off the top, and the onboard speaker looked like a large herbivore had sat on it. Totally flattened out and all the wires broken. It was a 25Ω speaker, which is an unusual size. More on that later.

A visual inspection of the board showed no obvious breaks and other than the crushed speaker, nothing that was a smoking gun.

Time to break out the oscilloscope.

Probing around I could see data on all address and data pins, so I assumed it was mostly working. I jumped on the forums to see what help I could get, and the friendly crew there were very useful!

First up they suggested I try the RAM test diagROM. This needed a speaker, so I cobbled together something out of two 50Ω speakers, in parallel. (These had ben purchased for the Microbees)

Unfortunately the diagROM produced no tones. I wasn’t sure if it was my speaker setup or the rest of the system, but the picture hadn’t changed.

(I had, by now, made up an RGB cable and had it plugged into the 15kHz LCD)

I went over the RAM chips, one by one, and one looked a bit out of kilter to the others, so I whipped it out, dropped in a socket, and tested again. It was worse. This turned out to be a timing issue, and the original RAM was fine.

At this point I was very suspicious of the custom ULA chip. Now these are still available, so I wanted a spare anyway, so I ordered one and waited…

Eventually a friend lent me one as an interim, and… no change. Still dead.

I was hoping this wasn’t going to turn into another “albatross” project that hung around my neck and never came to anything.

In desperation, I tried the diagROM again. No change. Then a different diagROM. No change. No beeps. I checked my ROM against known good ROMs. It was fine.

In desperation I tried something odd. I tried no ROM at all. This should have caused the system to pretty much halt straight away. But I was still seeing activity on all the pins…

It didn’t look like RAM. The ULA had been swapped. The only thing left on the bus was a 6522 Versatile Interface Adapter and the CPU. I doubted the 6522 could cause what I was seeing. Could it be the CPU?

I desoldered the existing CPU and dropped in a socket. Many of my systems use a 6502 CPU, but I didn’t want to have to gut a working system if I could avoid it. Conveniently I had an old 1541 floppy disk drive in storage that had a very dodgy power supply, so it had been demoted to “parts” and it had both a 6502 and a 6522. I tested both in my Vic 20 to confirm they were “known good” and both passed fine.

The moment of truth!

I dropped in the 6502 in the socket, powered it up and…

Huzzah! Even my speaker was working!

I wasn’t clean and clear, unfortunately. It turns out there is very little space in the Atmos case, so I had to remove the RAM socket and solder that RAM chip directly to the board.

Next there was a fault with the keyboard. Eventually I traced this to two broken traces on the keyboard PCB. Presumably done when whatever stomped the speaker was stomping around.

While one I was able to fix with some fresh solder across the bridge, the other one ended up needing a bridge between the connector and the keyboard switch. I just used a length of wire-wrap wire to do this.

At this point everything got a good clean and polish and it was looking pretty good. (Or so I thought… Dun dun dunnn)

I hot glued the speakers to the underside and internally we were complete.

I made a quick Android to Tape adapter that I could plug into the system to load games and away I went!

I have since purchased a SVI-CAS cassette emulator, which I can use with all my tape based systems, but it has excellent compatibility with the Oric.

I’ve also started 3D printing temporary keycaps to replace the missing keys.

While fitting these, I realised that what I thought was textured plastic around the key bases was actually a mixture of dirt, hair and something greasy. Much isopropanol and cotton tips later, and it’s pretty good.

I’ve run out of resin for now so the rest of the caps will need to wait.

486DX40

This one was a fun one! It keeps on giving.

Another friend dropped off “an old computer” to me. He figured the most valuable thing in it was probably the Tape Backup unit. I was actually more interested in the rest of it!

It’s a “Zeuss” branded 486DX40 with a VESA Local Bus (VLB) motherboard.

When I got it there was some minor corrosion from a leaked battery, but it was very minor. I did the usual “Wash with vinegar, the distilled water, then isopropanol, then dry in the sun” process I always do in these cases. All the tracks were fine, and as the board came with a pin header for an external battery pack, I just used that, rather than replace the battery.

As it came configured, there were no VLB cards in it, which was an odd choice. It did boot and seemed to run OK.

I formatted the hard disk and set about seeing what upgrades were available locally. Amazingly two local friends were able to get me both a VLB Video card and a VLB Multi I/O card for this system. (Hi Matt! Hi Matt!)

(If you’re not of the right circumstances or age to have encountered systems of this vintage, there were no peripherals at all on the motherboard of the average computer. Everything had to be slotted in via cards. VLB was a much higher speed bus compared to the older “ISA” standard that predated it. VLB Video and Multi I/O means the hard disks controllers and the video were able to run as fast as they could, with the bottlenecks not being their connection to the rest of the system. The Multi I/O card includes a floppy disk controller, an IDE Hard disk controller, serial and parallel ports.)

You can see the empty VLB connectors at the top of the picture, in brown. the legacy ISA slots are at the bottom in black. VLB card use both the ISA slot and the VLB slot.

Here’s the CPU. I have added a heatsink since this, to keep it cooler. It seems to do an admirable job.

I also found a nice ESS soundcard, and it’s currently doing a good job.

The only thing I haven’t managed to do is get either of my ISA network cards working, which is a bit frustrating.

I added a Gotek drive to replace the floppy disk, and recabled everything neatly.

It’s running DOS 6.2.2. I might add Windows for Workgroups later.

About the only thing I find a little pokey is the CPU isn’t quite fast enough for me to play System Shock 1 on. Oh well. It was free!

BTW the Tape drive has already been grabbed by someone who wants it for one of their setups. Waste not, want not :-D

SuperPAK Core Board

Suzy Jackson designed a new replacement Core Board for the Microbee family of computers (And also FreeBee, but that’s another story) which embraces and extends the designs of the PC85b to their logical conclusion. To wit, it offers ROM positions for 128 8K ROM programs (or, with work, you can swap 2x8k for 1 x 16k or 3x8k for 24k programs)

Upon seeing this, I coughed up the really cheap price Suzy was asking for them and added myself to the list. Due to an unfortunate encounter with “spicy cough”, the person who picked up my board was delayed in being able to drop my board to me, but that was a blessing as it gave me a chance to order all the parts from Mouser.

Suzy has made an excellent assembly guide for this and it was a breeze to follow, and so one afternoon after work, I ran together the board.

I populated it with the BASIC ROMs from my current PC85 board and fired ‘er up.

Works first time!

I have since filled the first 3 ROM locations with games, and will tinker with it more to fill as many as I can. It’ll be an awesome “instant on” Microbee games machine.


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2 responses to “Ketchup”

    1. Cheshy Chesh Avatar
      Cheshy Chesh

      Thanks! I need to do them more often. I just don’t seem to have the time any more :-)

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