So, as mentioned at the end of Recreating the Colecovision, a friend was interested in making one … so long as it came as some sort of ‘kit’. I then went and started ordering various bits and pieces. I often use various Chinese ebay sellers these days. One of the things I ordered were some more breadboards. Ebay and aliexpress seem to be full of various sellers selling MB-102 type breadboards. These are often very cheap ; around the $2 to $3 price range, and perusing the wider electronics-ee blog sites, a lot of people seem to use these … or ones that look like MB-102s. What could go wrong?
Now I had already ordered some of these MB-102’s from an aliexpress seller some time back. My initial impression is that they were ‘passable’. The atypical solid core ethernet wires I was using (24AWG) tended to feel a little loose in the breadboard holes compared to the ancient 30yr old+ breadboards that I probably bought from Jaycar when I was younger, but stuff seemed to work on the MB-102s … and I just needed to be more careful about bumping wires … as they were more easily dislodged.
So those first MB-102’s I bought were in use, so I ordered some more from ‘yet another ebay seller of cheap electronics stuff’. These newer ones I could kind of tell were not manufactured in the same factory. They kind of looked the same, but the little plastic bits that are meant to click them together didn’t click so well, and I thought my 24AWG wires were even looser in these boards.
Anyway, in prep for this ‘kit’ I was making, I built (or started to build) another Colecovision on a set of MB-102 breadboards. It all kind of went reasonably well up until I wired the 9929A and 4164s in. At the black and white picture test phase I was just not getting a picture at all or sometimes I would get some artifacts on the screen that looked a bit like the game that was supposed to be running. I tried running lots of wires from the GNDs of the 4164’s back close to where the PSU GND wires entered the board. I would occasionally get a slightly better picture, but it was still a mess.
On a hunch, I pulled out the 9929A and 4164’s and put them on a spare older breadboard I had (yet another ‘over 30yr old’ one). ie. I left the Z80A and other chips on the MB-102 boards.
I had a working Coleco! I then thought about all the differences between this 30 yr old breadboard and the MB-102 one. Sure wires feel loose when you put them in the MB-102s, but the whole Z80A, ROM, RAM and various other logic was working perfectly with these MB-102 boards. Then I thought maybe its the GND plane stuff … but I had added a lot of wires seemingly to improve the GND plane but it did not help.
So then I removed the 9929A and 4164s from the old breadboard and put them back in the MB-102. Sure enough it was broken again. I knew the Z80A was seemingly working OK because 5 or so seconds after power on the screen would go a light grey colour which corresponds to the blue ‘press 1 for one player, difficulty 1 …etc’ screen. But I could not see any characters. Well sometimes I would see bits of characters. It was a random garbage mess.
Then I started looking at the power consumption figures for the 9929A and the 4164s. The 9929A has a nominal current of 200mA, and the eight 4164s may pull around 200mA all together. That is quite a lot of current for a breadboard … especially in one spot. After trying a few things I tried adding more wires to connect the power bus strip to the GND pin of the 9929A (ie. there are three short blue wires going to the GND pin instead of one)
And that pretty much made the Coleco work with the MB-102 board. I still think it is a bit marginal, but it made a world of difference.
So, even though I was chuffed that I had somehow figured out what was going on, I thought my friend is unlikely to be amazed by getting a $3 breadboard to do something, so I went and ordered some more breadboards … this time from element14 (hoping that I would get ‘quality’ ones). I ordered some expensive-ish Wisher WBU-201J breadboards and some cheaper Multicomp MC01000 boards. The idea was to test these with the 9929A and then send some to my friend.
So the test case was to leave the Z80A, ROM, RAM etc on the existing MB-102 boards, but to construct the 4164s, 9929A and a simple transistor amp for black and white video on each of the breadboards below. From left ; a generic MB-102 from ebay, a transparent SYB-120 from ebay, the Multicomp MC01000 (the packaging it came with has ‘Shuiyuhpu’ written on it), the Wisher WBU-201J and the 30yr old board I found in a cupboard.
So the basic outcome of this testing is;
- generic MB-102 – pretty much a fail, but if you add extra GND wires to the 9929A GND pin and cross your fingers then maybe it might work.
- generic SYB-120 – Ooops, I didn’t test this one (I started to put the 9929A and 4164s on it, then realised that it is missing a 2nd power rail on the right hand side that makes it annoying to wire up. Perhaps I’ll try and test it another time).
- Multicomp MC01000 – Works perfectly. Great value
- Wisher WBU-201J – Works perfectly.
- Really old crappy rusty breadboard – Works perfectly.
Re the MB-102’s,
- There is probably some manufacturer out there that makes a good one … but a zillion other clone manufacturers have cloned it, and attempted to cut costs to the point where you get a breadboard which is nothing like a decent quality one.
- For a lot of modern electronics work you will never hit the problem I hit with the MB-102 purely because your current consumption will be far less. Like I said, they work fine for the Z80A, ROM and RAM sections (which consume less current). But in theory I am potentially trying to pull close to half an amp (9929A plus eight 4164s) … and this seems to be ‘almost’ too much for a poor MB-102.
For now, I am going to send three Multicomp breadboards to my friend as I know they will work really well, and I might order some more.