Falcon mb board capacitance after power off

[Rustynutt]

Going to post this here, it's an issue as far as me being stupid :lol:
Posted in another forum, Exxos forum is much more active hardware wise, should have asked here in the first place. :oops:

Was having an issue with the Afterburner 040 booting after a crash and cycling power. Normally it's consistent. Power off, wait, power on.
Using a voltmeter, it looks like the Falcon board takes about 30 seconds to completely bleed down voltage across this (Falcon) board.
Is that average, or does this board possibly have a failing capacitor? I've replaced the main and a few other "large" ones recently, but not all.

Successful reboots of the AB and power decay time to 0Vcc seem connected. Thus, always the wait.
If 30 seconds is a normal drain time, is it possible to use a cap across the 5Vcc rail to ground somewhere to pull this down faster?
(Know nothing about circuits).

I've seen this anomaly with a CT60 installed. After power off, you can hit reset within a few seconds, and watch the CPU fan give a slight spin.

Output is at 4.92Vcc up and running.

However, noticed when double clocking the AB 68040 from 24MHz to 48MHz, the CPU pulls the power level down to 4.90Vcc, 20Mv.
Is that getting too close to a low voltage for the Falcon to operate correctly? From memory, most my stock machines were about 4.92Vcc.

Another stray voltage I came across was with a second IDE 3.5" drive connected using a 40 to 44 adapter.
It's powered by a separate ATX supply. I noticed with the Falcon off, I'm seeing about 15MV across the 5Vcc rail with the ATX on.
The 3.5 inch drive is only connected by the IDE cable, so how is 15MV coming across? The data lines? Or possible the ground between the two supplies, but then why does the 15MV show up on the Falcon's Vcc?

With the ATX off, the AB boots reliably within the 30 second cycle off/on period. With the ATX on, it's hit and miss.

Thanks for any magical enlightenment.

[exxos]

Sounds like your reset circuit caps probably need changing on the Falcon or at least increasing as per the general fixes ? If it works by pressing the reset button after power up then it is pretty conclusive in that case.

I don't know why the power supply voltages are so low and drops further under greater load. Sounds like some sort of regulation problem. Has the power supply re-capped ? Indeed I have found issues with the DFB1 ( which I still need to confirm actually) seems to point towards it misbehaving at 4.90V. I did design a power supply adjuster board to alter the voltages on the power supply but as always just too many projects and not enough time.

But alas I don't know anything about third-party accelerators so cannot really advise why it malfunctions.Indeed it does sound like those screwy issues with the CT60 as well.

[Rustynutt]

Exxos,
This particular board has not had the reset circuit reworked, so will give that a go.
The PS has not been recapped, however do have one of the larger capacitors bulging a bit at the top, guess I should change it before it blows up in my face :)
Thanks!

[exxos]

The PS has not been recapped, however do have one of the larger capacitors bulging a bit at the top, guess I should change it before it blows up in my face :)

Aside from the caps being old, its a common misconception that caps are faulty which bulge on the top. The plastic covers warp over time due to heat. So you cannot use the plastic tops as a indicator of the caps health. The metal tops are slotted and can be used as an indicator.

In my old job we used to pull the covers off to see if the caps had really blown. Though I don't really recommend that for high voltage caps .

[Rustynutt]

The PS has not been recapped, however do have one of the larger capacitors bulging a bit at the top, guess I should change it before it blows up in my face :)

Aside from the caps being old, its a common misconception that caps are faulty which bulge on the top. The plastic covers warp over time due to heat. So you cannot use the plastic tops as a indicator of the caps health. The metal tops are slotted and can be used as an indicator.

In my old job we used to pull the covers off to see if the caps had really blown. Though I don't really recommend that for high voltage caps .

Appreciate that info. Not sure where the thought came from, possibly seeing an exploded cap, and it (obviously) bulging at some point.
My belly seems to do that often as well. Usually, pizza has something to do with it though :lol:
That, and just plain inexperience.

Not wanting to jump back into a DFB thread, we were discussing what's the point of a few MHz.
On my pedicular Falcon setup kind of goes like this, with respect to video modes.
Using my method of just swapping out the COMBEL oscillator for bus/CPU acceleration, and the Afterburner installed, 46MHz is the maximum clock (so far) tolerated without the Falcon (actually Afterburner) freezing once the PMMU is configured, and fast ram is loaded into the system.

At 23 MHz bus, there is just enough bandwidth to obtain 640*400 TC mode using a patch program (HRTC) dml /Black Scorpion wrote way back for use with the Nemesis.
Downside is at that speed, screen artifacts are pretty bad.

HRTC is handy for use with Nemesis (or Mikes brew, guess it needs some kind of Birdy num num name :D) or like on Steves Phantom setup.

Without the Afterburner installed, just going 2MHz more (48MHz oscillator), almost all the screen artifacts disappear, or make viewing the screen much much more tolerable in 640*480 TC VGA mode.

At 50MHz, screen artifacts completely disappear at 640*400 in VGA TC mode.
Here, ImageCopy, MPlayer, Apex Media, Apex Viewers and pretty much any other graphics or DTP programs that can display images or art are greatly enhanced, at least from the standpoint of utilizing a reasonable TC mode on a VGA monitor.

So in this case, just 4MHz makes a world of difference, one where not being lucky enough to have a SuperVidel stings quite a bit less.
(Happen to own one, so it's not the driving force behind this madness)

Now, on a stock machine, go for the gusto. On this well abused Falcon, I've owned since before 1995, have cautiously tested up to a 64MHz oscillator.
I've not tried to enhance resolution beyond the initial goal of 640*480 TC using Screen Blaster (or what's it called).

Did some Gembench test, and just seat of the pants test in TC mode at 32/64MHz. You'd swear you were working in 4 color mode speed wise, and bench test support it.

Only silicone that gets warm is the 030, and very. The rest are no warmer than if using the stock oscillator.
And it's stable that those speeds.
Other than SCSI. The upside is, before accessing the SCSI chain, simply run a small program to set the COMBEL to 1/2 clock output.
Bingo, error free SCSI.

The past few days finally had time to test this with the CT60e installed. Haven't gotten answers from anyone with respect to exactly how far, if at all does the CT read TOS in ROM before taking off on its own.
One little quirk is the program I use on the Afterburner, and stock Falcon to set the COMBEL to 1/2 clock causes an exception error on the CT.
Think I know why, but some more digging to do. Maybe ask on the dead hacker's site, see if evil (think he's the one that brought CT TOS to V1.05).
Getting past that, then would say using "Birdy Num Num", and Screen Blaster an SV-less CT owner would be quite happy having TC in VGA modes.
Before I forget, accelerating the bus does not affect the CT speed, it remains the same. Obviously :)

[mikro]

Haven't gotten answers from anyone with respect to exactly how far, if at all does the CT read TOS in ROM before taking off on its own.

Not sure what more is to answer than I already did in the PM to you; the answer is: nothing, TOS ROM is disabled, all content is read from the flash rom.

see if evil (think he's the one that brought CT TOS to V1.05).

It was insane/tscc: https://insane.tscc.de/

[Dlfrsilver]

On ST and Falcon, most of the time, the bad surprise comes from under. You will only see it when you disolder the caps. However, there is a good way to spot a cap that has buldge :

The hint is that the plastic package with the values (uf / V) around the aluminium body of the cap is retracting down showing the top aluminium of the cap. It shows that the cap has seriously heated.....