DKB Cobra reboot issue - caused by overheating?

[mingle]

Hi,

Yesterday my DKB Cobra 40MHz starting behaving is a slightly worrying manner, for no apparent reason:

When I performed a warm boot (CTRL-AMIGA-AMIGA) the system woudl start to reset (the green power LED would dim) but then nothing, just a blank screen.

Then I turned the power off (cold boot) and the same thing.

I had to power off and unplug the PSU for about 30 seconds before I could get it to power up. But I still had the same warm boot issue. Somethime I could get a warm-boot if I held the CTRL-AMIGA-AMIGA keys down for around 5-10 seconds.

The only thing  can think of is perhaps the board/CPU was overheating, since it was around 10-15 degrees C hotter yesterday. Or possibly the (weedy!) 22W A1200 PSU was also feeling the heat?

Does this sound possible?

Cheers,

Mike.

[Damion]

Could be a PSU, but as a preliminary measure I'd probably try removing the card and cleaning the motherboard contacts with a q-tip and some ISO. Also, try re-seating the RAM and oscillator on the Cobra (if it's socketed).

[mingle]

Hi,

Yeah, I tried all of the obvious things first.

Without the Cobra card installed the system seems to be fine, so the issue must be either a fault with the card or the PSU being too weak to drive it.

But it was working fine prior to yesterday - the only difference I can see is that it was a hot day (inside and out!).

Can heat affect the power supply?

Cheers,

Mike.

[Azryl]

Hey.. why blame the poor Cobra card
check the temp of your Power Supply Brick!!

Holding down the cntrl-amiga-amiga keys for about 10 seconds gives the PSU brick time to smooth the voltage supplied to your amiga. So it will reboot.. but very soon after the brick will throw a wobbly again once amp draw is pulled especially the 5volt line. If the 5volt is struggling in hot weather the Amiga will not boot properly

Place the PSU brick up off the surface its sitting on, put little feet under it to help promote convection airflow from underneath to the top. Common cause of A1200/600 and A500 poor booting is power, not flakey connectors on the motherboard or expansions.

It was rather warm in Melbourne yesterday. So check your PSU temp!

Az

[mingle]

Hi Az,

Thanks for the info...

The PSU didn't feel particularly hot, but it is one of teh really wimpy 22W ones. I have the DKB Cobra (40MHz) plus 16MB of RAM, plus the Ferret SCSI adaptor and an IBM 4GB HDD - does this sound a bit much?

It's a pretty warm one again today and the A1200's been misbehaving a  bit again.

The CPU on the Cobra card was too hot to touch, but this may be normal, I don't know...

I might have a go at rigging up an old ATX power supply to give it some more juice...

Cheers,

Mike.

[Azryl]

I have bought small heatsinks from dicksmith or jaycar and used small dobs of hotmelt glue on the corners to stick them to the tops of 68030.

On the A1200 the lisa chip is the hottest running chip on the mobo. By sticking a small heatsink on top of lisa I have reduced alot of the heat related problems regarding A1200's.

Australia is a hot climate to be running any computer system, especially a passively cooled system like the A1200. Any help we can give makes them run better and probably last longer.

Az

[Damion]

Yes, it could be an overheated or failing PSU, and testing it, taking measures to cool it, etc, are all good ideas.

Common cause of A1200/600 and A500 poor booting is power, not flakey connectors on the motherboard or expansions.

Sure, flaky connections can cause all sorts of problems, particularly on older amigas (A500/A2000/etc) with all the socketed chips. Another factor on the A600/A1200 are tired caps, especially if you have an older Commodore board, symptoms of which may be more pronounced with expansions connected or a marginal PSU. (Don't mean to preach on this oft-repeated subject, but I've acquired 2 A600 motherboards in the past year that were practically ruined from damage caused by the leaking electrolyte. The Escom A1200 boards are still "new" enough for this not to be as big an issue, but any A1200 from the C= era should have those babies replaced ASAP.)

[terminator4]

the 22W one?  likely your problem.  A accel based A1200 needs stronger p/s.  there's a fellow in australia (amigamaniac.com) that sells adapters so you can use a pc p/s.  i think for $15 aus its worth it considering you won't pay much for postage ;-)

[mingle]

Luckily (?) mine is a late Escom A1200, so hopefully it'll be okay for a while longer!

@Az,

Do you have any pics or more detailed info on the heatsinks and how you go about selecting/fitting them?

When you say hotmelt glue, do you mean using those glueguns that take the hard glue-sticks? Does that stand up to the heat generated by the ICs?

Cheers,

Mike.

[Fingers]

Holt-melt glue...well...melts!

JayCar sell self-adhesive heatsinks, buy those instead :-D

Pick one roughly the size of the chip, peel off backing sheet, place on chip. Couldn't be easier than that.

PZ.

[motrucker]

I have used a 40MHz Cobra with 128Mb of RAM for to many years to remember, and never had a problem. My 030 has never gotten hot to the touch either, warm yes - hot no. Is yours still actually running at 40MHZ
I use a Bigfoot PSU - A great addition but that has nothing to do with how hot the CPU runs.
Try putting a small fan inside, and see if that helps?

[rkauer]

 I can swear the PSU is the culprit in this case.

 Buy an adaptor or hack yourself a new PSU for your Amiga.

 In hot climates like ours (south Brazil is very hot in the summer, too cold on winter, obviously), is always a good preventive measure to stick some heatsinks on the hottest chips (Lisa, Alice, CIA and the orig. CPU).

 Accelerator parts goes hot, too.

[stefcep2]

The PSU *may* be the problem but I had an A500 PSU using the same cobra card in Melbourne and in summer after variable period on, usually under 20 minutes, my A1200 would freeze.  The COBRA was brand new from Computamagic.  Eventually they put a heat sink on the CPU, but I also took off the trap door cover and used rubber feet under the A1200 to lift it up.  It still failed especially when doing cpu intensive stuff eg rendering.  I ended up selling it with 16 MB ram and fpu for $180: it cost $400.  If you can figure a way to get fan to work over the CPU that would probably be more effective.  At this stage its 70 % overheating cobra/ 30% weak PSU. BTW I ended up getting an Apollo 1240 40 mhz which ran without problems on the same A500 PSU for years even though the 68040 sucks more power than the 68030.  I vowed not not to ever buy another DKB product again.

[weirdami]

The only thing I know abot these A1200 rebooty problems is that those trapdoor items can get mega hot and can cause a reboot type situation. So, I pop in to threads like this and say something like:

If you put milk jug caps under the feet, the card in the trapdoor can get air.

I think there was a running gag around here years ago about broccoli ties or something, too. Your air space under space creation technique may vary.

[mingle]

Hi All,

Thanks for the many and varied comments and suggestions! :-)

Today (about 15 degrees cooler than yesterday!) it's been a bit better.

I've still to muck around with the PSU (converting an old PC PSU) to confirm it's at fault...

The only issue seems to be rebooting - once it's up the A1200/Cobra will run fine without any issues (touch wood!) apart from the CPU getting very warm...

I've always found DKB stuff to be very good - the documentation with the Cobra is admittedly pretty poor, but my old DKB1202 RAM/clock card was very well made and came with great documentation.

Cheers,

Mike.