Sold Commodore 1581 drive mainboard kit replica.

[MCes]

The marked "74LS14" are C-Mos clones, into the not powered "LS" ics the inputs result electrically insulated,
but the C-Mos input pins have ESD protection diodes that "clamp" the pin to Vcc line, so if Vcc become zero the input pin will force the line to zero, imagine this on serial lines, or on reset lines (the vic20 will be reset)

No.

Chinese fake/rebranded chips are CMOS clones. Genuine 74LS chips purchased from authorized distributors use BJTs - NOT CMOS - and accordingly consume more power. They also all have pull-up resistors in all inputs.

If you buy all your logic chips from Amazon or eBay from Chinese vendors then you may think all 74LS chips are CMOS clones. real ones are NOT.

- - - Updated - - -

I buy my chips from Digikey or Mouser only.

Zero stock Expected 3/24/2022

AFAIK, the 74LS14 used in Commodore 8 bit drives can be replaced with 74HCT14 and both Digikey and Mouser have them in stock.

DO NOT use the 74HC14 because the logic threshold level is 1.5V with 74HCT and it is 2.5V with 74HC when powered at 5Vdc.

See: https://learn.sparkfun.com/tutorials/logic-levels/ttl-logic-levels

I was not clear:
74LS14 is TTL and is not C-Mos,
the chips that have problems are marked as "74LS14" but they are not 74LS14:
they are C-Mos clones, so also 74HCT14 can't work for the same reason: you have to use a TTL gate, a C-Mos gate (74HCT14) will having the same issue, independently by the threshold level.....

 

[Deleted member 14264]

the chips that have problems are marked as "74LS14" but they are not 74LS14:

Makes sense now.

 

[MCes]

I was not clear:
74LS14 is TTL and is not C-Mos,
the chips that have problems are marked as "74LS14" but they are not 74LS14:
they are C-Mos clones, so also 74HCT14 can't work for the same reason: you have to use a TTL gate, a C-Mos gate (74HCT14) will having the same issue, independently by the threshold level.....

View attachment 169427View attachment 169426

No.

See: https://www.onsemi.cn/pub/collateral/an-368cn.pdf

Try it and then write the results.... good luck



So.....

 

[pazuzu72]

no more sales of this item can go ahead until you have made contact to either stop selling or resolve the issue.

If that's okay, you can put SOLD on this thread.
I am redesigning the PCB to be the copy of the original 1581 in addition with my own modifications.
When it is ready I will update the thread.
If this is not allowed you can delete the thread.

 

[Deleted member 14264]

Try it and then write the results.... good luck

View attachment 169429View attachment 169428

So.....

I put 74HCT14 in all my C64 and IEC drives and it works just fine. Don't know what you do to get this result.

Also, the 1541 Ultimate (and II and II+) use CMOS chips to connect to the IEC bus. They too have clamping diodes and they have no problems.

You must provide power to your chips for the tests to be valid.

 

[Sardine]

no more sales of this item can go ahead until you have made contact to either stop selling or resolve the issue.

If that's okay, you can put SOLD on this thread.
I am redesigning the PCB to be the copy of the original 1581 in addition with my own modifications.
When it is ready I will update the thread.
If this is not allowed you can delete the thread.

sounds ok to me.

 

[MCes]

Try it and then write the results.... good luck

View attachment 169429View attachment 169428

So.....

I put 74HCT14 in all my C64 and IEC drives and it works just fine. Don't know what you do to get this result.

Also, the 1541 Ultimate (and II and II+) use CMOS chips to connect to the IEC bus. They too have clamping diodes and they have no problems.

You must provide power to your chips for the tests to be valid.

I am sorry.... exactly NOT!
here we are responding exactly to this case:
why the serial connection fall on all devices connected if only one is switch off, but only if it is not fitted with a real TTL 74LS14?

1581 replica boards received, thank you. International shipping was pleasantly fast with respect to how packages are moving lately.
One note though, the 74LS14 provided was marginal, had to replace to allow correct operation > issue was 74LS14 gate locking up IEC bus when drive not powered up but still connected to IEC bus.

 

[Deleted member 14264]

I am sorry.... exactly NOT!

Can we get less emotional here please.

here we are responding exactly to this case:
why the serial connection fall on all devices connected if only one is switch off, but only if it is not fitted with a real TTL 74LS14?

Yeah, that makes sense. It also explains why the 1541 Ultimate carts would have no problem as they get power from the cartridge port. Unlike an external drive it gets power from the cartridge port so it can't be off when the C64 is on.

If you have an external drive which is off on the bus while the rest is on, a 74HC/74HCT will bog it down. This means you can put a 74HCT14 in place of the 74LS14 in the C64 but you can't do it in a drive if you expect the drive to be turned off when the C64 and other drives are on.

1581 replica boards received, thank you. International shipping was pleasantly fast with respect to how packages are moving lately.
One note though, the 74LS14 provided was marginal, had to replace to allow correct operation > issue was 74LS14 gate locking up IEC bus when drive not powered up but still connected to IEC bus.

So this would indicate the 74LS14 was in fact a rebranded CMOS chip from dear friends in China. Same problem as described in this video: https://youtu.be/Knfv-Qp7Q2U

 

[Deleted member 14264]

Mouser appears to have just received a massive stock of more than 10'000 SN74LS14N in DIP-14 package.

 

[MCes]

I am sorry.... exactly NOT!

Can we get less emotional here please.

here we are responding exactly to this case:
why the serial connection fall on all devices connected if only one is switch off, but only if it is not fitted with a real TTL 74LS14?

Yeah, that makes sense. It also explains why the 1541 Ultimate carts would have no problem as they get power from the cartridge port. Unlike an external drive it gets power from the cartridge port so it can't be off when the C64 is on.

If you have an external drive which is off on the bus while the rest is on, a 74HC/74HCT will bog it down. This means you can put a 74HCT14 in place of the 74LS14 in the C64 but you can't do it in a drive if you expect the drive to be turned off when the C64 and other drives are on.

1581 replica boards received, thank you. International shipping was pleasantly fast with respect to how packages are moving lately.
One note though, the 74LS14 provided was marginal, had to replace to allow correct operation > issue was 74LS14 gate locking up IEC bus when drive not powered up but still connected to IEC bus.

So this would indicate the 74LS14 was in fact a rebranded CMOS chip from dear friends in China. Same problem as described in this video: https://youtu.be/Knfv-Qp7Q2U

I am happy to read that you also now agree with my technical analysis.

well, now we know why it is important to use real TTL chips on serial connection devices.

 

[Deleted member 14264]

I am happy to read that you also now agree with my technical analysis.

well, now we know why it is important to use real TTL chips on serial connection devices.

I do. I think this is just different symptoms to the same problem.

Chinese vendors offer logic chips for sale that are marked as 74LS or 74S and what you really get are chips that were made before 2004 - so not RoHS compliant - and really 74HC. The threshold level is wrong and they have clamping diodes.

For many applications it changes little to nothing but it definitely poses a problem here (a single drive turned off on the IEC bus) and wherever the threshold level makes a difference.

Warn everyone you can about this issue as many people buy this junk for new cloned Commodore boards for both computers and drives. People building new Amiga boards will be affected too.

 

[Wes256]

Sorry for stirring the pot here, I've been repairing Commodore gear forever and this is a very common issue, drives loading down the EIC bus when connected to the bus but not powered on but usually on older 1541s, the 74LS14 is of the first I suspected right after the 7406 open collectors, another common failure IC in the IEC communication circuitry.

 

[pazuzu72]

Prototype of my smd version of the 1581 board (size 100 x 80 mm). Allows you to connect both a standard and a slim drive.
It seems to work correctly. I'll do a post sale when I'm done. Maybe someone is interested in some project.