Amiga 500 Hardware Problem - Advice Please

[GadgetUK]

Hi,
 
I've recently purchased an Amiga 500 and a 1200, and before I started using them i've started restoring them... Long story short - I am working on the A500 at the moment.
 
Upon testing Turrican (original disk) with the A500 I noticed that it crashes on loading - the title shows fine, with the lightning etc, then there's the 'Wecome to Turrican' sample, fine again, then it starts to load and before the main title screen displays it hangs, the sound stops and repeats the last few bytes etc for a few seconds, the power light flashing 3 or 4 times at the same time, then it reboots to the guru screen.
 
If I connect a 512Kb fastram board it actually boots up fine and is playable. The thing is i've noticed problems on other games as well, they load so far and eventually reboot, nearly always at the same point. Lotus III for example will load to the start of the race, you drive forward for like 2 seconds and then it crashes.
 
The state of the PCB is very good - although I've just replaced the following sockets due to a drink having been spilt on them many years go by the looks of things. CIA (nearest Denise), Denise socket, Fat Agnus socket, and Paula socket. All of these have been done after the initial fault, and the state the Agnus socket was in I suspected that a new socket would solve the problem, but its exactly the same as it was. These have all been replaced very very carefully using a desoldering station and it looks good as new and every contact looks fine (no lifted pads, very clean replacements i've done).
 
I've also got 2 complete sets of the chips - ie. 2 x Fat Agnus, 4 x CIA, 2 x Gary, 2 x Denise, 2 x Paula, 2 x CPU. So i've gone as far as swapping each chip and re-testing just to ensure there's not some really obscure problem with one of the main IC's. It's just the same...
 
It's a rev 5 board, but the keyboard looks to be from an older model - its the one with a red power LED which goes off when the audio filtering is enabled. I've rules this out by disconnecting it and booting witout it - same problem. Also swapped the floppy drive just to rule that out and same issue.
 
I've just removed and socketed 1 of the RAM chips but its not that one (15 to go...), but does this sound like it could be a RAM problem? What I am puzzled by is that when fastram is there turrican loads, but I thought chipram and fastram were used for very different things within the system - ie. CPU has only access to fast ram, which could mean that fast ram takes priority for code over chipram, and possibly having fastram connected means I am skipping the CPU loading code into dodgy ram perhaps, is that what I am seeing here?
 
I thought the A500 was supposed to test RAM on boot and give a green screen if there's a problem?
 
Any advice appreciated because the way this is going I am going to end up chucking the damn thing out of the window lol.

[Oldsmobile_Mike]

Sounds like you've done some very good work!  Based on your first couple sentences I'd also suspect a RAM problem, but just to rule out some quirk with bad disks or whatever on your games, if you boot to a Workbench disk is the machine stable?  I.e., if Workbench runs for hours and only the games crash, it might be something else.

Unfortunately I don't know of a good memory testing program, but am sure someone else will come along soon who does, LOL.  

[GadgetUK]

Sounds like you've done some very good work! Based on your first couple sentences I'd also suspect a RAM problem, but just to rule out some quirk with bad disks or whatever on your games, if you boot to a Workbench disk is the machine stable? I.e., if Workbench runs for hours and only the games crash, it might be something else.
 
Unfortunately I don't know of a good memory testing program, but am sure someone else will come along soon who does, LOL.

Thanks, it's definitely not the floppies, i've rules that out, and the fact that Turrican fails every time at the same point without the 512Kb of fastram connected leads me to believe that it's a chipram / addressing issue.  I am wondering if the logic chips that sit on the 'data path' part of the board could be the issue - do those ever fail?

I will continue swapping (and socketting) the RAM chips for now, but they are a pain to remove - Agnus socket was far easier lol, and that was difficult enough...

[paul1981]

I've just removed and socketed 1 of the RAM chips but its not that one (15 to go...), but does this sound like it could be a RAM problem? What I am puzzled by is that when fastram is there turrican loads, but I thought chipram and fastram were used for very different things within the system - ie. CPU has only access to fast ram, which could mean that fast ram takes priority for code over chipram, and possibly having fastram connected means I am skipping the CPU loading code into dodgy ram perhaps, is that what I am seeing here?
 
I thought the A500 was supposed to test RAM on boot and give a green screen if there's a problem?

It doesn't test the ram byte by byte, as that would take far too long. You'll need a memory testing program for that, and aminet would be a good place to look for obtaining one (there are many). Someone else can perhaps point you in the right direction for the best program to use.

And on the A500, any trapdoor ram expansion isn't Fast ram at all, despite being known as Fast ram by the system. It's actually as slow as Chip ram and is known as "slow ram", as it's connected to the same bus as Chip ram. It's quite useless really, so many people do the modification on their A500's to turn that 512k slow ram into Chip ram that can used as Chip ram (more sound samples, more screens open etc etc).

[Ral-Clan]

Just to be thorough, I'm going to ask an obvious question:

You said you had both an A1200 and an A500. You're not trying to run the AGA version of Turrican on the Amiga 500, right?  That will certainly crash (and often when it reaches the same point on disk).

I would see if your Amiga can load a bog standard Workbench disk, then run a mem checking utility from Aminet.

[GadgetUK]

Just to be thorough, I'm going to ask an obvious question:

You said you had both an A1200 and an A500. You're not trying to run the AGA version of Turrican on the Amiga 500, right?  That will certainly crash (and often when it reaches the same point on disk).

I would see if your Amiga can load a bog standard Workbench disk, then run a mem checking utility from Aminet.

Haha, thanks - good point but I am not that stupid lol.  I had an Amiga 20 years ago, many of the disks i've used on the a500 before, and Turrican 1 was for the original Amiga.  Going to put memtest on a floppy using the 1200 later, and will test that in workbench.  I hope it reveals a problem.

Edit:  Also, read my first post - it does not crash if I have 512Kb of fastram, so theres no way its the AGA version, or a dodgy floppy.

[AmmoJammo]

Has the board already been modified so the trap door ram is chip ram?

I imagine that could create issues if the trap door ram was then not installed, but I could be wrong :p

[GadgetUK]

Has the board already been modified so the trap door ram is chip ram?
 
I imagine that could create issues if the trap door ram was then not installed, but I could be wrong :p

No, it's never been touched - well, except for coffee many years ago by the looks but that's got little to do with the fault I think.
 
I do think its RAM, or one of the logic IC's that sit on the 'data path' part of the board.  I've just spent an hour messing around trying to copy MemCheck from the PC, to the amiga 1200 HDD and then to a floppy...  I finally managed it, booted the 500 up with WB1.3, and then ran MemCheck - it needs KS2.04 or greater, ARGHHHHHHHHHHHHHHHHHHH!

[GadgetUK]

OK, a bit of progress but not there yet...  Temporarily piggy backing the RAM I found a RAM chip that was causing Turrican to hang on loading when not having fastram connected.  After socketing that chip and putting a new 41256 in Turrican loads fine =)

The bad news is that Turrican has a few wierd sprites - randomly, hard to recreate.  And Lotus 3 still crashes around 2 or 3 seconds after race start.  I suspect another RAM chip probably but the tester ive tried crashes as soon as you run it =\

[GadgetUK]

More progress!!  Using other games (Lemmings and Rolling Thunder) and using the piggyback method I found 2 more faulty RAM chips.  Those games now work perfectly, as does Turrican.  Days of Thunder has a corrupted game screen =\. Yet every other game i've tried has worked fine, excluding Lotus 3, which still crashes after a few secs of race start - it has a wierd double road thing going on as well where you see a 'ghost road' to the right of the main road, its very odd.  I cannot find any more faulty chipram on the board so the Lotus problem might be the fastram board at fault (cleaned bat acid off it already so wouldnt suprise me).  Just dont get the problem with Days of Thunder now =\

[Matt_H]

I'm assuming you're using PAL machines and PAL versions of the games? I've experienced similar problems when running PAL games on an NTSC Amiga. Once the machine is booted into PAL mode, everything works fine. So just make sure you're truly dealing with a hardware problem and not a software one

[GadgetUK]

I'm assuming you're using PAL machines and PAL versions of the games? I've experienced similar problems when running PAL games on an NTSC Amiga. Once the machine is booted into PAL mode, everything works fine. So just make sure you're truly dealing with a hardware problem and not a software one

 
Thanks, yes, these are PAL version.  Mostly originals which came with the A500 but I already had a collection from around 20 years ago.  
 
It's really frustrating because I am almost there but not quite...  I keep inching towards it being perfect but i've got these issues, and I am sure there's either another RAM problem or possibly something else wrong with the system.  The thing is you start to question your previous work - like I am now starting to wonder if i've killed a track somewhere under the Agnus, or under Paula etc, even under the 3 RAM chips i've replaced so far.
 
So far everything else i've tried runs fine except for Lotus III - which used to play fine on my A500+, and interestingly enough i've tried the same game (using PD .adf images instead) in UAE and I see the same sort of crash where the picture goes all coloured noise, a bit like a TV noise pattern but with colour before it shoots off and you get a crash.   Additionally there's Days of Thunder which loads OK, sounds OK, even plays OK but the dashboard of the car is part of the title screen image in the wrong colours - it's very wierd, almost like it could be a RAM problem but I cannot be sure.  I tried the piggyback method again against that fault to see if it would rectify but it didn't, but that could mean that some of the RAM has shorted rather than gone open circuit.  
 
Finally there's the fact I cannot run sysdiag as it crashes the machine also.  Does anyone know of a ram tester that works with KS1.3?  I've tried a few now and they seem to only work on 2.04+
 
I think ultimately I am going to end up having to remove all of the RAM now =/   I don't mind removing sockets etc they are far easier.  The problem with RAM is it absorbs the iron heat and you nearly always risk pad damage unless you do it really carefully.  Where I can take a 48 pin socket off in 10 minutes, its taking like 45 minutes per RAM socket =/

[Azryl]

Just a quick question. Are these games 1meg games or 512k games?  Some will not run without all the ram available that they require.

And some games might require 1meg chip ram to run, if cracked and not originals.

Az

[GadgetUK]

Just a quick question. Are these games 1meg games or 512k games? Some will not run without all the ram available that they require.
 
And some games might require 1meg chip ram to run, if cracked and not originals.
 
Az

Days of Thunder is an original, and I know that needs 512Kb of chipram only because i've tested in emulators.  Lotus III will work with 512Kb of chip and fast(slow) ram because i've played it on other a500's before.
 
I suspect if i've still got a problem with chipram, and possibly a problem with fastram.  I've got another 512Kb fastram + clock in the loft, I will get it down later, but it's anyones guess as to what the battery has done to that board =/

[GadgetUK]

I am on the home run now!  I found another game that had major graphical corruptions.  I ended up socketting all of the remaining RAM chips, only when I got to the very last chip did the corruption vanish after I tried a good chip in the socket.  The Days of Thunder corruption is still there but Lotus 3 is massively improved - can play for 2 or 3 mins now before it crashes and there are no graphical issues.  I suspect 1 of the chips I thought was OK isnt.  Just need to swap 1 at a time tomorrow until Days of Thunder looks OK.

I've also had to order 2 ceramic caps (0.33uF) to replace 2 that broke.