Mega ST4 - no video output at all

[stephen_usher]

Hi stephen_usher, I was to ask about this, are the 41256 compatible with the memory on the Mega ST4?
Mine has the TC511000AJ10, which is 1Mbit x 1, right?
I do have some 41256 here, and will buy more, but as you said, piggybacking can help. I saved my A500 doing this.

Oh, of course, they're 1Mbit on the MegaST. oops!

About the CAS lines, pin16 I checked them yesterday and got nothing.
The RAS lines, pin 3, has activity.

With no activity in CAS I saw it was connected to the 74LS244 (U59).
Probably this IC is faling as the traces to CAS lines from it to MMU are ok and MMU IC is working, tested on my 520 ST.

Does this sound right?

Well, no CAS no memory. If you've got the CAS from the MMU entering that chip and nothing coming out then that would point to that chip being the problem.

I find this location has decent schematics https://docs.dev-docs.org/htm/search.php?find=_s. Specifically the "Atari Mega ST4 schematic (C100166, Rev A) [1987]" one is clear.

[rubber_jonnie]

Hi stephen_usher, I was to ask about this, are the 41256 compatible with the memory on the Mega ST4?
Mine has the TC511000AJ10, which is 1Mbit x 1, right?
I do have some 41256 here, and will buy more, but as you said, piggybacking can help. I saved my A500 doing this.

Does this sound right?

Comparing pinouts, the 511000 and 41256's are very different, and I don't think I've ever run into Mega's that use 41256.

[Badwolf]

The only problem I have to purchase these "must have utilities" hardware is living in Brazil.
For each £ I need seven of my money (R$ - Brazilian Reais).

The exxos cart has a lot of other cartridges combined on it. If you only need the ST one, you may be able to source one locally cheaper?

BW

[asapreta]

Hi stephen_usher, I was to ask about this, are the 41256 compatible with the memory on the Mega ST4?
Mine has the TC511000AJ10, which is 1Mbit x 1, right?
I do have some 41256 here, and will buy more, but as you said, piggybacking can help. I saved my A500 doing this.

Oh, of course, they're 1Mbit on the MegaST. oops!

About the CAS lines, pin16 I checked them yesterday and got nothing.
The RAS lines, pin 3, has activity.

With no activity in CAS I saw it was connected to the 74LS244 (U59).
Probably this IC is faling as the traces to CAS lines from it to MMU are ok and MMU IC is working, tested on my 520 ST.

Does this sound right?

Well, no CAS no memory. If you've got the CAS from the MMU entering that chip and nothing coming out then that would point to that chip being the problem.

I find this location has decent schematics https://docs.dev-docs.org/htm/search.php?find=_s. Specifically the "Atari Mega ST4 schematic (C100166, Rev A) [1987]" one is clear.

I got a lot of schematics there and also the service field manual.
I only didn't get the REV.A one as I thought it was an older one and my board is REV.5, so I used REV.7 :(

And yes, these DRAM will be a pain...

[asapreta]

The only problem I have to purchase these "must have utilities" hardware is living in Brazil.
For each £ I need seven of my money (R$ - Brazilian Reais).

The exxos cart has a lot of other cartridges combined on it. If you only need the ST one, you may be able to source one locally cheaper?

BW

I doubt it!
I was lucky to get this ST4 here in Brazil!
But I will get one from exxos as soon as I can.

My former 1040 STe and my actual 520ST I bought in UK.
Good times the currency was "good"..

[asapreta]

Hi stephen_usher, I was to ask about this, are the 41256 compatible with the memory on the Mega ST4?
Mine has the TC511000AJ10, which is 1Mbit x 1, right?
I do have some 41256 here, and will buy more, but as you said, piggybacking can help. I saved my A500 doing this.

Does this sound right?

Comparing pinouts, the 511000 and 41256's are very different, and I don't think I've ever run into Mega's that use 41256.

Yeah, as the Mega uses 1Mbit DRAM, I need to find compatible ones.
A fast Googling I got these:

µPD421000 D421000 NEC 1Mx1
TC511000 TC511000 Toshiba 1Mx1
GM71C1000 GM71C1000 Goldstar 1Mx1
TMS4C1024 TMS4C1024 TI 1Mx1
HM511000 HM511000 Hitachi 1Mx1
HY531000 HY531000 Hyundai 1Mx1
KM41C1000 KM41C1000 Samsung 1Mx1
M5M41000 M5M41000 Mitsubishi 1Mx1
MB81C1000 MB81C1000 Fujistu 1Mx1
MCM511000 MCM511000 Motorola 1Mx1
MSM511000 MSM511000 OKI 1Mx1
MT4C1024 MT4C1024 Micron 1Mx1

Now I need to check the "China Supplier"...

[rubber_jonnie]

Now I need to check the "China Supplier"...

Paid a visit to their store already today...

[stephen_usher]

Before you do anything with the DRAM you need to get the CAS signal working. It's quite possible that this is the problem and not the RAM chips.

Without a CAS signal the DRAM won't work at all as it won't select the column address and won't refresh either.

If you have a spare 74LS244 try piggy-backing that on top of U59, it can't hurt.

[rubber_jonnie]

Before you do anything with the DRAM you need to get the CAS signal working. It's quite possible that this is the problem and not the RAM chips.

Without a CAS signal the DRAM won't work at all as it won't select the column address and won't refresh either.

If you have a spare 74LS244 try piggy-backing that on top of U59, it can't hurt.

Yep, got to agree with this.

[asapreta]

Before you do anything with the DRAM you need to get the CAS signal working. It's quite possible that this is the problem and not the RAM chips.

Without a CAS signal the DRAM won't work at all as it won't select the column address and won't refresh either.

If you have a spare 74LS244 try piggy-backing that on top of U59, it can't hurt.

Sure, this is the priority.
I do prefer removing it because it is a logic IC not a DRAM.
A 4-5 minute job.

I never have piggybacked logic ICs before, wouldn't the outcome be the same as the badchip ?
DRAMs don't do logic, so piggyback is fine with them.