Fix it 'til it's broke...

Having had a little dry spell on the retro front I went back to fiddling with the A500+ Rev8 board I repaired a while ago. All I was going to do was plug it in with a floppy drive and boot up some games and generally mess about - as long as no keyboard required though since I don't actually have a spare..

A500+ Goodness.

Anyway, after setting it all up, I found a bit of a problem. The floppy drive didn't work. Or, at least, the drive would try to boot but then declare that the inserted disk was not a DOS disk. Hmmm. After several other disks displaying the same behaviour I realised I had a genuine fault somewhere which wasn't there when the board was first repaired about a year or so ago. Marvellous.

Not a DOS disk? Oh, really?

First thing to try, a different floppy disk drive. Well, I currently have three so I thought it would be just a case of a dodgy drive, dirty heads or whatever. But to my surprise, all three drives gave me the same results. So it's not the drive then.

Hmmm. Next thing. Could it be the CIA chips aren't in right? Re-seated them. No difference. In fact I reseated all of the chips but it still made no difference. Even though the Agnus socket was broken I was fairly confident she was still making good contact with all her pins.

Next. 

A close examination of the floppy connector revealed a couple of suspect looking joints, so I broke out the soldering iron and reflowed all the pins, just in case. But no change.

Next.

Could it be that a CIA is actually faulty? They come in pairs so swapping them over is a good way to see if the fault moves to a different part of the board. So I swapped them over but the fault stayed on the floppy drive and did not move to the keyboard or anywhere else.

Next.

Time to break out DiagROM. This should tell me if there was a problem with the CIAs and the floppy drive. The tests on the CIAs did seem to be telling me there was a problem. The timing tests were failing and it was repeatable. And, more importantly, it changed when I swapped the chips.

DiagROM Test 1 - Slow and Fast CIAs..

DiagROM Test 2 - CIAs swapped
but there's still an issue

There are two CIA tests in DiagROM so I swapped the chips back and tried again:

DiagROM Test 3 - Failed

DiagROM Test 4 - Failed again..

But then I put the two CIAs from this machine into a Revision 6 board that I have and also put in the DiagROM. Both CIAs passed without problem. Hmmmm. This was annoying as it meant that both CIAs were probably OK and that there must be something else wrong.

CIAs in a Rev 6A - They pass. WTH?

Back to the A500+ board and time to look at the DiagROM drive diagnostic section. This actually didn't tell me very much either. I could see the floppy drive but it would not access it properly. The author of DiagROM kindly responded to a query I put on the Amiga Facebook group that the floppy drive parts of DiagROM aren't the best and he was looking to re-write and improve them at some point.

In desparation I got the schematics out and looked at the lines running to the floppy connector in the hope that there could be something there to give me a clue but to no avail. I also did try swapping out the logic IC that deals with the selection of the internal and external drive.. But the original chip actually tested OK on my slightly Heath-Robinson tester board contraption and the replacement made no difference either.

The logic chip 74LS05 was OK. :(

Swapping out Paula and Denise with known working spares made no difference either.

Then I de-soldered the two transistors in the circuit to see if one of those had failed. But they came up fine too on my el-cheapo component tester.

Transistors within normal parameters..

So, finally I had to go and get my precious hard disk from in the house and bring it out to my workspace. The reason for this was that I knew it had Kier's test disk on it. I could boot to Workbench, run the test app and maybe see what the heck was going on.

Initially, I was fairly successful but it was obvious something was not right. The app crashed (never done that before) and when it actually worked many of the drive test functions didn't seem to work properly. 

GURU! GURU! GURU!

Crash! A-aaar!

I was ready to put this board on 'broken for spares' pile at this point but then I came across someone on the Facebook group who had had a similar issue on an A600. It turned out that he had a missing line on the data bus. Could this be the same on my board? 

A quick blast on Excel generated a data line test sheet. The idea is simple, just check continuity from and to the points on the spreadsheet. If there's no continuity then that's most likely the source of the problem. 

Finally. A use for Excel!

And would you believe it, I was missing data line D9. A bodge wire to restore D9 was implemented...

Coated copper wire. Saviour?

It works!

And it worked. Perfectly. So, there are a couple of takeaways here. Firstly, always check your data lines. And secondly, just because you think you've cleaned all the battery spillage off a board, don't assume you have. I can only assume this was the cause of the break in D9. But it's back to working properly. 

Atari Jr Part 2 - Or "How to kill a retro games console..."

So, my Atari Jr is working but is stuck on black and white. No amount of fiddling with the TV switch will change the monochrome output to colour.

Road Runner - but in black and white

Meep.

This may have been down to the rather 'clunky' composite mod that I installed. This consisted of several resistors and a capacitor, somewhat clumsily soldered to the board in various places. I was, frankly, amazed that I got anything output that a TV could understand.

Man, that is ugly.

To get around the somewhat amateur nature of my mod I ordered a deluxe composite mod kit from the rather nice chaps at The Future Was 8-Bit. This has a rather nice discrete circuit board that contains a simple circuit to split out the composite and audio signals. This deluxe version has a simple connector with four flying leads and a 3.5mm four pole jack that accepts a composite/audio cable to simplify connecting to a TV even more. Nice.

Lovely composite mod kit.

Sorry chaps - you're no longer required.

All that's required is a few components to be removed as per the full colour instruction leaflet and then the four cables installed in the indicated locations. Easy.

Nearly ready to go..

This I did, but to my disappointment the output remained firmly in monochrome. After examining the board I noticed that there were several long solder 'whiskers' on the end of the pins of the cartridge port on the motherboard. I simply tidied them up with a quick touch of the soldering iron on each pin.

And that killed the console. Dead.

If you turn on a working Atari Jr with no cartridge then you get a grey square with no sound in the middle of the screen. Well, it turns out that this is also what my Atari Jr decided it would do from that point on too, even with a cartridge installed. Dangnabit.

It's dead (again) Jim.

I have no idea what happened - and I remain open to other ideas - but I think that either I somehow managed to zap one of the chips with static (I have some carpet in the work area I'm in) or one of the chips was starting to die - hence the monochrome output - and it just so happened to finally die after I cleaned up the pins of the cartridge port. Or maybe the shorted cap I found caused some damage? Who knows.

Either way, it's dead.

Back to eBay where I managed to find another Atari Jr for less than the cost of one of the TIA chips. Go figure. But it was a typical 'unit only, untested, worked when I put it away' but for the price it was worth a gamble.  After a few days it arrived and, as luck would have it, it had the exact same revision of board... more or less. I won't dwell too much on this bit as I basically just took the board, cleaned it up and then applied the composite mod to it, and stuck it in my cleaned case.

Unit number 2 - note missing silver label

Difference 1 - small cap now has its
own place on the board

Difference 2 - small cap is in different
location 

Difference 3 - voltage regulator looks
like a 1A rather than 0.5A

I did briefly toy with the idea of de-soldering the chips to put in my original board but I was too concerned that, if they are fragile, I might destroy them and be back to square one.

So I temporarily attached the composite mod to the new board. And....

Let's try that again, shall we?

Colours, so many colours...

Success! So, all that's needed now is to carefully solder the mod in properly and put it all back together.

Wires fed through the handy hole in the board

Wires trimmed, soldered into place

and secured with hot glue (I'm not proud!)

The connector board gets heatshrunk (shrinked?)

Cable connected up

I decided that I would put the cable connection inside the case and leave the cables permanently connected. The cable just needed to be fed through the case. To give some strain relief I wrapped it around one of the screw pillars which seemed to hold quite firmly.

Cable hidden in case

Finally, the cable fits perfectly through the 'channel 3/4' selector hole. This is not used by UK models and so is empty anyway. Looks almost like it was made for it..

Cable exit.

 One final test, and we're done.

MEEP! MEEP! This time in colour. :)

Atari Jr - Sorry I can't think of a fun title.... - Part 1

My 'bio' over in that corner over there says that I'm an Amiga Nut. This is true, but it doesn't necessarily mean that I was a Commodore fan-boy. Not me. My computer life started with a ZX Spectrum + in about 1984, then progressed to the SAM Coupe (now ultra rare, very expensive and we threw it away in about 2004 - don't ask...) and then the Amiga before succumbing to the PC.

But then I realised that, even with a couple of diversions into consoles like the ever early Interstate that my Dad bought in the early 80's and my Nintendo Gameboy that was a Christmas present in 1992, I have never owned anything by Atari.

Until now.

Ahhh - so small and cute!

This little - and it is surprisingly compact - guy came from eBay. Console only, untested. As usual. It's an Atari 2600 or more frequently known in this configuration as the Atari Junior.

After acquiring a couple of el cheapo games (Road Runner and Pole Position), I attempted to plug it in and see if it showed any signs of life. It's important to know that my usual composite mod wouldn't work since the later consoles mix the audio with the video signal before passing it through to the modulator, so the best I could hope for was to see the power light light up.

First thing, it's 9v DC with a 3.5mm jack instead of the more usual barrel connector. Presumably this was cheap for Atari but you ran the risk of shorting out the console if the power was on and you pulled out the power cable. This is one of those times where you really should follow the 'always switch off the power at the wall before removing the power cable' advice...

Anyway, I got my trusty power supply out with the 3.5mm jack (the same as for the Interstate - but the Interstate is 'tip negative') and checked twice that the polarity was correct for the Atari i.e. tip positive or centre positive. Now, my power supply has a little LED indicator lamp on it that lights when it gets plugged into the mains. But when I plugged it in after putting the cable into the back of the Jr this light stayed dark. How odd.

But I persevered and switched on the console.

Nothing. Nada. Zilch. Zero. Zippo. Dead.

It's dead Jim.

I quickly switched it off and unplugged the power supply from the wall and disconnected the cable from the back. I scratched my head for about 30 seconds before I realised that this was almost certainly a dead short somewhere on the board. After hunting down my multimeter I put it in continuity and started probing around. First thing, try the power socket. Sure enough, the terminals gave a dead short. But where would that short be?

This is one of those times where I got lucky. The board has a large capacitor just next to the power switch so I thought I'd de-solder it and see if it was still good as it was big and easy to get to. So I removed it with my trusty de-soldering tool, and.....the short disappeared. WHAT?

Capacitor - is this a dagger I see before me?

Out came my little component tester. Clip in the cap and press the button... and it says that the 2200uf capacitor is actually a 0.12 ohm resistor. Oh. So the cap has gone bad and gone full short. Again, I fell lucky as I actually had a small bag with EXACTLY the value of this capacitor, even down to the voltage so I was able to easily replace it.

Nope - it's a dead short..

Second time 'smoke test' - power light stays on on the power supply and power light comes on on the console. Nice. Now all I need to do is figure out the best way to do the composite mod.

Well, the power LED works at least...

There are, as I have found out, several ways to skin a cat. Some require minimal components but also seem to be minimally documented, some require kits of parts from nice suppliers on the intertubes. To begin, I tried to keep it simple and cheap.

First, take a handful of resistors and a 100nf capacitor. Add them to the board in the correct config. Attach a wire to the appropriate point on your resistors and then solder it to a new phono socket. Solder a wire from ground to the ground on the phono socket. Job done. (Video of this mod from youtube and can be found here.)

It's not exactly pretty....

Ugly. Urgh.

But does it work?  Kind of...

Meep! Meep!

I can get quite a decent picture but it's only in black and white. Now, the 2600 experts among you may remember that these consoles actually have a switch to switch between colour and monochrome - a definite throwback to when colour TVs were not that common. But I did check and it was in the correct position.

So, it's either that the mod isn't quite right (highly likely), the TV type switch is borked (possible) and stuck on B&W or there is an issue with the video chip (worst case scenario).

Anyway, I also managed to get sound out of it by soldering a wire to pin 13 of one of the chips and then another to ground and connecting them both to another phono socket. So sound and video do both work.

It's Alive!

I still need to dig out my ZipStick joystick (compatible with this as this is the machine that invented 'Atari' style joystick ports - as used by many, many other manufacturers including Commodore for the Amiga), and I will probably look at building a better composite mod or even buying one of the many kits available.

To be continued....

Grandstand Adman TV Game 3000 - Now with COLOUR!

The 70's were a great time. The final Apollo missions. Skylab. Development of the shuttle. I was born etc etc etc. Good times.

But behind all the browns and headache inducing patterns the beginning of the computer games industry was taking place. First for the home came the Magnavox Odyssey, then Pong. Then someone cloned Pong to take advantage of an obvious market. Then someone else did. And another, and another. In fact, many Pong clones appeared. So many in fact, thanks to a couple of manufacturers who literally made Pong-on-a-chip. The most widely used of those was the General Instruments AY-3-8500. It's descendants appear in the Interstate console that I have (see HERE and HERE).

Well, GI wasn't the only company having a go at Pong-on-a-chip. Texas Instruments also had a go but with far more limited success. Their TMS-1965 chipset was not a huge success but was, strangely, pin compatible with the AY-3-8500.

So, anyway, a couple of weeks ago a box arrived.

What's in the box??

This is the Grandstand Adman TV Game 3000. It uses the TMS-1965 chipset and is surprisingly pleasing to look at. But I'm getting ahead of myself. There had been a 2000 model previously but the 3000 has colour (ooooh!) instead of just black and white. This is the late 70's though so expect greens, yellows and garish blues.

I bought it for the grand sum of £6.27 after realising that I have effectively been priced out of the market for most retro kit now. (An Amiga A500+ for £100??)

This particular unit has definitely been in storage in someones garage for some time judging by the state of it. It's very dusty and has that aroma that only a damp garage can generate.

Grungy..

Fortunately, this is quite a simple machine so I shouldn't have to worry too much about corrosion from errant capacitors or batteries.

Well, sh*t.

I spoke too soon. The unit had obviously been in storage for a heck of a long time. I haven't seen that style of battery for probably 20 years or more. But the question is, what damage has been done? Did I buy a £6.27 paperweight (that's no good as a paperweight without all that - er - weight)?

No Damage! - Phew!

Fortunately, the batteries in this console are to the front and below the main board(s). Also, I can only assume that the previous owner had it stored the correct way up otherwise we would have been looking at a total disaster.

Let's start the clean up. First, remove the case and snip off the controllers. They only have four wires each so it's easier to remove them for this work. I also left some wire on the board as these circuit boards are 40 years old and sticking a hot metal stick on them may cause unnecessary damage. It's much easier to solder two wires back together than try to repair a heat damaged trace. 

Controllers Separated

Next, remove the main halves of the case and wash them in warm, soapy water with the controller covers and let them dry through properly.

Washing Up

The case came out surprisingly well. I actually really like the look of this console. It may be from the 70's but the size and shape appeal to me far more than some 70's kit (looking at you Binatone...). I even managed to keep the 'QC' sticker. :)

Clean and Fresh.

Next thing to do is work out if this unit can output composite. It's an odd thing that most ancient games consoles generate a perfectly usable composite signal that is then hammered into RF. I suppose most TVs in the 70's and early 80's didn't have the array of inputs that modern TVs had. But in any case the pattern for this type of console is broadly similar:

1) Look for the TV modulator. It might be a silver box or even just a bit of circuit board but it will be where the TV output is.

2) Look for the two main connections into it. In most cases one lead will be for power to the modulator circuit and one will (probably) be the composite video signal.

To test this one I took my multimeter and plugged the unit in (9v D.C. centre pin negative a' la ZX Spectrum). Then I measured the voltage on both of the connections. One was a steady 5.01 volts and the other was wavering at about 1volt. So I disconnected both wires and connected the one with 1 volt to the centre pin of the TV out connector with a bit of orange wire. 

Orange Wire Composite Mod.

Will it work?

Looks good!

Of course. :)

So, now I'd proved it works all I had to do was re-attached the controllers and put it all back together.

There's not a lot to these...

Back in the case

Controllers attached and working

Done. Almost..

The only thing left to do with this is clean off the polystyrene from the cables. Apparently, the plastic on the cables contains a 'plasticizer' that leaches out of the plastic and gets absorbed by the polystyrene causing it to melt. The same happens if you wrap a cable around a plastic box. Eventually the cable starts to melt into the plastic.

I also have the box for this but it's in a really sorry state. I may have a go at repairing it and washing the polystyrene inserts. If I do I'll just update this post as I suspect a dedicated post about taping up a 40 year old box is possibly a bit dull, even for me...