Is anyone else seeing a huge power fluctuation?

Other boosters or variants.
Post Reply
User avatar
stephen_usher
Posts: 5580
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Is anyone else seeing a huge power fluctuation?

Post by stephen_usher »

I'm seeing this rather large power and ground spike being generated by the TF536. It's precisely 2us after /IPL2 goes low.
IMG_2078.jpg
IMG_2078.jpg (211.11 KiB) Viewed 3537 times
(Both traces have 0V at the same level on the 'scope, the blue is +5V and yellow GND.)

I know it's being generated by the TF as if the processor is idle (or if /IPL2 is inactive) there's no spike.

If I switch my processor board over to the 68000 then there is no spike even though /IPL2 is operating in the same way and shows the same signal strength. (Though there is a very small ripple at that point.)

So, is anyone else seeing something on the power rails?
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
User avatar
stephen_usher
Posts: 5580
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: Is anyone else seeing a huge power fluctuation?

Post by stephen_usher »

OK. Found the issue. It was my 10K pull-up on the /RESET line. I removed that and the spike disappeared, at least from the power. There's still a spike on the /RESET line.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
User avatar
stephen_usher
Posts: 5580
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: Is anyone else seeing a huge power fluctuation?

Post by stephen_usher »

Nope! Not that, it's back again.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
User avatar
exxos
Site Admin
Site Admin
Posts: 23496
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Is anyone else seeing a huge power fluctuation?

Post by exxos »

If you connect your scope to GND (both GND and probe) what do you get on the scope then ?
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
User avatar
stephen_usher
Posts: 5580
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: Is anyone else seeing a huge power fluctuation?

Post by stephen_usher »

Both on the TF then it's a flat 0V, as you would expect. The spike is relative to the PSU and ST ground.

The resistance between TF GND and ST GND is 0.2 ohms.

P.S. I've cut the +5V trace which goes right across my board and I'm powering that line from a pin right next to the socket. That short (~2 cm) trace is picking up the noise on the ground fill it's passing through when left unpowered with nothing in the socket.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
User avatar
exxos
Site Admin
Site Admin
Posts: 23496
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Is anyone else seeing a huge power fluctuation?

Post by exxos »

The TF536 has a solid gnd layer, and half the inner layer is 5V the other half is 3.3V. So its got a huge slab of copper there. Spikes from PSU ground to basically anything will likely have spikes. Its why caps are important to give a low impedance down to a supply point. The whole TF board is referenced to system ground so the spikes you see are not really a problem at any point. If the system GND spiked 2 volts, then the whole TF536 ground would do the same, so the noise isn't really there as such. As long as the spikes are not on the PSU side, or TF side, then there isn't anything you can really do about it anyway. The only noise on the TF rails would probably be <100mV or something. Depends on how good the regulator is.
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
User avatar
stephen_usher
Posts: 5580
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: Is anyone else seeing a huge power fluctuation?

Post by stephen_usher »

I wouldn't be so worried if the spike wasn't showing up on at least some of the address lines on the ST's own bus.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
User avatar
exxos
Site Admin
Site Admin
Posts: 23496
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Is anyone else seeing a huge power fluctuation?

Post by exxos »

Is this is a original ST then every signal is bad.
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
Post Reply

Return to “EVERYTHING ELSE”