Amiga 600 game port up and left not working

[frasbo]

Hi.. hoping someone can help me. So I have an amiga 600 which has been recapped and has been working fine for a few years now. Today I went to play it and noticed that the left and up aren't working on the joystick. I tried a sega mega drive gamepad and same behaviour.

I took the amiga apart and checked all the pins on the game port have continuity with a multimeter and they all appeared fine. Checked all the caps and resisters close to the game port and I'm finding a connection for each of the pins so they all appear ok. I cleaned all the board with some IPA and and a light brush and now I notice that if I push up-left on the joystick this works but still to movement if I individually press left or up.

Any ideas?

[Boing-ball]

Hi.. hoping someone can help me. So I have an amiga 600 which has been recapped and has been working fine for a few years now. Today I went to play it and noticed that the left and up aren't working on the joystick. I tried a sega mega drive gamepad and same behaviour.

I took the amiga apart and checked all the pins on the game port have continuity with a multimeter and they all appeared fine. Checked all the caps and resisters close to the game port and I'm finding a connection for each of the pins so they all appear ok. I cleaned all the board with some IPA and and a light brush and now I notice that if I push up-left on the joystick this works but still to movement if I individually press left or up.

Any ideas?

First off get hold of Amiga Test Kit which is downloadable for free. Stick this in a Floppy disk or USB thumb drive (If you have a Gotek drive). Boot this up where you can test the controller ports. Also run a CIA test. Possibility you may have a problematic CIA chip. Note that it is not advisable to be plugging Joysticks in and out of 9pin ports when the Amiga is switched on 😉

Failling that. Get hold of something called DiagROM which can be plugged in instead of the kickstart ROM which will also do tests like the CIAs etc.

[frasbo]

Thank you I will try this all out. Much appreciated.

Ive ordered a parallel 2 port joy stick adapter off ebay in the mean time - do you know if this will get round the issue? Or will this also use the CIA?

Also is it easy to replace CIA chip with just a solder iron? Or will I need hot air station etc...

[Boing-ball]

Thank you I will try this all out. Much appreciated.

Ive ordered a parallel 2 port joy stick adapter off ebay in the mean time - do you know if this will get round the issue? Or will this also use the CIA?

Also is it easy to replace CIA chip with just a solder iron? Or will I need hot air station etc...

The parallel 2 port joystick port is only for games that support 4 player mode. Therefore it won’t fix your problem. As for CIA chips, they will need to be removed with a hot air station. But check that it is a CIA problem first.

[Castellen]

The CIA is an unusual suggestion, these have nothing to do with joystick/mouse movement input in any Amiga model.

There are 4 movement inputs (up, down left, right) that are read by U4 (Denise) in the A600, and these four inputs are multiplexed to eight inputs (for both ports) by U34.  If an input isn't working, it's either a fault with U34, or more likely, the input signal isn't getting to U34.

It's simple to fault find.  Use a DC voltmeter to measure between ground and U34 pin 11 (joystick up) and pin 10 (joystick left).  They'll be at 5V with no input, and at near 0V when the input is activated.  If those inputs of U34 are changing but there's no movement reported, it's a fault with U34, which needs to be replaced; about 30 seconds work with a SMD rework station.

If the input signal isn't getting to U34, it can be a problem with corroded pins in the joystick connector, cracked inductors (E365, E367 in this case) or possibly PCB damage, all of which you can pin point using the voltmeter to see where the input signal is not getting to.  With the computer powered off, you can also measure continuity between joystick connector pins 1 to 4, which should connect to U34 pins 11, 14, 10, 13 via 68 Ohm series resistors.

It's also worth checking the solder joints on the 9-way connector.

In the case of cracked inductors, which sometimes happens, you can just remove them and bridge the PCB pads with a piece of wire.  In this part of the circuit they're only there to reduce conducted radio frequency emissions as part of EMC compliance.  The input will function exacty the same with a wire bridge in place of the inductor.

[F0LLETT]

One question, do you have a 1MB RAM expansion?
If so remove it and see if issue is resolved. Seen loads of this type of issue with dodgy trapdoor connection issues with RAM card.

[frasbo]

Many many thanks for such a detailed responce. This will give me a great way to troubleshoot the issue.

Thanks again - I will update once I get time to try this out.

[frasbo]

No not got the 1MB ram expansion but thank you for responding.

[frasbo]

Just to give an update on this issue;

So I ordered the U34 chip from ebay (from a seller in Italy) - I managed to remove the chip with a soldering iron without ripping the pads (I don't have access to Hot Air Station) by flooding the chips pins with solder, wicking up the solder and slowly lifting each pin. I replaced the chip but the behaviour still persisted with up and left not working on the joystick.

So in my frustration I attempted to repeat the process as I received 5 chips from Italy but this time I ripped about half the pads the chip sat on - I attempted to retrace these and a put a new U34 back on - at this point it was a total mess and now the mouse only half worked and only fire worked.

So I had to send off my Amiga 600 to Luke at Retro Six for repair (Cost me £60) - who I can't recommend enough (Guys is a Wizard with this stuff!)

He posted a tik tok video of the repair on the retro six tick tok page (also his facebook page) of him repairing my mess.

He also mentioned to me that the resistor on the MV1 line (68R termination resistors) had burned out which he said is starting to be very common.

Hope this helps someone!

Thanks for the help from the previous people who replied.

[F0LLETT]

Guess he means M1V. Have to be fair, worked on hundreds of A600's. Never once had an issue there.
Sometimes the 4.7 Ohm 5V feed resistor, but thats generally when someone shorts out 5V rail when inserting metal mouse or joystick connectors.

Just to give an update on this issue;

So I ordered the U34 chip from ebay (from a seller in Italy) - I managed to remove the chip with a soldering iron without ripping the pads (I don't have access to Hot Air Station) by flooding the chips pins with solder, wicking up the solder and slowly lifting each pin. I replaced the chip but the behaviour still persisted with up and left not working on the joystick.

So in my frustration I attempted to repeat the process as I received 5 chips from Italy but this time I ripped about half the pads the chip sat on - I attempted to retrace these and a put a new U34 back on - at this point it was a total mess and now the mouse only half worked and only fire worked.

So I had to send off my Amiga 600 to Luke at Retro Six for repair (Cost me £60) - who I can't recommend enough (Guys is a Wizard with this stuff!)

He posted a tik tok video of the repair on the retro six tick tok page (also his facebook page) of him repairing my mess.

He also mentioned to me that the resistor on the MV1 line (68R termination resistors) had burned out which he said is starting to be very common.

Hope this helps someone!

Thanks for the help from the previous people who replied.

[Castellen]

Guess he means M1V. Have to be fair, worked on hundreds of A600's. Never once had an issue there.

I've also worked on hundreds of A600 and haven't seen that either.  Not even sure how the resistor could 'burn out' in that position, it connects a low current TTL output to a high impedance input.  The original post suggested that the problem might have been intermittent, in which case it was more likely that the resistor was cracked as opposed to 'burnt out'; possibly lost in translation.  Obviously it can't un-burn out, then re-burn out again. Have seen plenty of cracked resistors and inductors before which can cause permanent or intermittent faults.

A bit more simple fault tracing would have confirmed if U34 was defective or not and would have avoided both the mess and expense.

[F0LLETT]

I've also worked on hundreds of A600 and haven't seen that either.  Not even sure how the resistor could 'burn out' in that position, it connects a low current TTL output to a high impedance input.  The original post suggested that the problem might have been intermittent, in which case it was more likely that the resistor was cracked as opposed to 'burnt out'; possibly lost in translation.  Obviously it can't un-burn out, then re-burn out again. Have seen plenty of cracked resistors and inductors before which can cause permanent or intermittent faults.

A bit more simple fault tracing would have confirmed if U34 was defective or not and would have avoided both the mess and expense.

Ah yes, cracked resistors. Bloody annoying. Going round in circles, checking components you know are going to be faulty. Only to find they read correctly, due to you pushing on them with meter probs, .