Woo hoo - Collection Completed!! TRS-80 inbound

[rubber_jonnie]

The expansion interface is always handy to have you can get cf card options as well for the trs80

Link to upgrades http://bartlettlabs.com/MIRE/


Tom

Oooh, nice.

[stephen_usher]

That's definitely looking promising.

I've found that 4116 chips just walk out at a whim. The TI99/4A I got worked for about 5 seconds when I first powered it up before a couple of the 4116s just died and a third one soon after. The 1970s technology with three voltages is just not robust.

[rubber_jonnie]

That's definitely looking promising.

I've found that 4116 chips just walk out at a whim. The TI99/4A I got worked for about 5 seconds when I first powered it up before a couple of the 4116s just died and a third one soon after. The 1970s technology with three voltages is just not robust.

So far my TI99/4a has been fine, so fingers crossed. I think the only other machine I have with 4116's is the Spectrum, but also, so far so good.

Just back from karate and off to dig out some 41256's, see if I can make it work :)

[rubber_jonnie]

Also, I'm hoping that the screenshot I got is showing that the screen RAM is fine, but just the main memory is in a mess.

[Tomswork]

The video ram is being read and displayed the machine will need to boot to clear and refresh it. The z80 uses the 16k of ram to store its registrer contests so it will not boot without the 16k block working


Tom

[rubber_jonnie]

The video ram is being read and displayed the machine will need to boot to clear and refresh it. The z80 uses the 16k of ram to store its registrer contests so it will not boot without the 16k block working


Tom

Thanks, confirms what I was thinking about the RAM. I did modify 2 41256s last night, but it's no better, so I think much more of the original ram is bad than I previously thought.

[stephen_usher]

This is why I bought one of those cheap RAM testers which does 4116 and 4164 chips. Second guessing a system when you have no idea if the RAM is OK or not doesn't get you very far.

At this point, if I were working on this, I would suspect that all the RAM is bad and replace it as a matter of course given the other potential issues with the system. Without known working RAM you don't have any firm base to stand upon.

[rubber_jonnie]

This is why I bought one of those cheap RAM testers which does 4116 and 4164 chips. Second guessing a system when you have no idea if the RAM is OK or not doesn't get you very far.

At this point, if I were working on this, I would suspect that all the RAM is bad and replace it as a matter of course given the other potential issues with the system. Without known working RAM you don't have any firm base to stand upon.

You're quite right and this is what I came to accept on the journey into work this morning. I do have a bunch of 41256 ICs I can re-work that are all testes and working, but I think I'll be investing in a 4116 tester, but I do already have a 4164/41256 tester built round an arduino.

[stephen_usher]

You're quite right and this is what I came to accept on the journey into work this morning. I do have a bunch of 41256 ICs I can re-work that are all testes and working, but I think I'll be investing in a 4116 tester, but I do already have a 4164/41256 tester built round an arduino.

The biggest problem with testing 4116 chips are the extra voltages. they're just a pain.

I got one of these: eBay link to DRAM tester @ £22

It seems to work well and catches about 90% of issues. It has problems catching a small number of address error failure modes but I've found it invaluable.

[rubber_jonnie]

You're quite right and this is what I came to accept on the journey into work this morning. I do have a bunch of 41256 ICs I can re-work that are all testes and working, but I think I'll be investing in a 4116 tester, but I do already have a 4164/41256 tester built round an arduino.

The biggest problem with testing 4116 chips are the extra voltages. they're just a pain.

I got one of these: eBay link to DRAM tester @ £22

It seems to work well and catches about 90% of issues. It has problems catching a small number of address error failure modes but I've found it invaluable.

Yeah, the multi voltage stuff is a huge pain. I've been hooking up 2 bench PSUs and the original PSU to get them all present and correct.

Have just ordered one of those testers, be interested to see the results, but I fully l expect all the RAM to be knackered.