Safety Reminder

[Zarxx]

These computers and devices we love are old and you can sometimes have problems, like I just did.

 

Luckily I was next to my 800 and hadn't wandered off when the burning smell hit me and smoke started pouring out the side.

 

[Mclaneinc]

What are those, rectifier diodes?

[Mazzspeed]

They look like diodes? It would make sense they were part of a rectifier.

 

It's a bit odd that a diode would fail so dramatically TBH. Personally, I'd be going right over the PSU in any 800/400 or even any original XL/XE PSU before use. Even then, I'd be turning power off at the wall when not in use.

 

Perhaps I'm just paranoid after a period of time where the hard wired smoke detectors in my house kept going off randomally at 2:00 in the morning. Eventually I worked out the insulation in the ceiling was getting into the detectors and setting them off.

 

By Gawd that wakes you up fast, let me tell you!

[Zarxx]

Been using the machine most of the last week no problems, including yesterday evening for several hours. Powered on this morning fine for an hour or so, then the problem started.

 

I replaced all my 9v AC psu with modern ones several months ago and not have any issues. I've checked the output ok of the one I was using but have swapped it for another.

I have a spare 800 and have swapped the power board and it all seems fine, problem is now is it going to happen again due to another possible fault, plus the lingering burning smell doesn't help as it warms up.

Edited July 31, 2021 by Zarxx

[Mclaneinc]

(Re Mazzspeed comment about fire alarms)

 

It does indeed, I live in a 3-storey block of flats and my rather annoying neighbours above do very strange stuff like make curries at 3 in the morning but don't keep an eye on the food, so it's all too regular that their smoke alarm goes off and scares the hell out of us. And like you, if my old computers are not in use they are unplugged from everything, I'm grateful they have survived 40yrs but don't like taking chances..

 

OT: There's a new Ultimate+ (3.10) update, supports D71 and D81 files and lots more, read the manual, some changes in the cart side..

Edited July 31, 2021 by Mclaneinc

[Rybags]

That is a rectifier diode.

 

Re "replaced my 9V DC PSUs..." - the early machines use a 9V AC power supply so ensure that's what you've replaced it with and that it can also match the current requirements - if it was DC going through there then CR208 would be the sole diode handling the incoming angry pixies.

Edited July 31, 2021 by Rybags

[Mclaneinc]

7 minutes ago, Zarxx said:

Been using the machine most of the last week no problems, including yesterday evening for several hours. Powered on this morning fine for an hour or so, then the problem started.

 

I replaced all my 9v DC psu with modern ones several months ago and not have any issues. I've checked the output ok of the one I was using but have swapped it for another.

I have a spare 800 and have swapped the power board and it all seems fine, problem is now is it going to happen again due to another possible fault, plus the lingering burning smell doesn't help as it warms up.

Yup, that smell is a real confidence killer..

 

Looks like it was hit with a massive surge, but I'm not very electronically knowledgable..Seeing there's 4 of them, I'd presume rectifier side, but to explode like that..eek...

Edited July 31, 2021 by Mclaneinc

[Zarxx]

1 minute ago, Rybags said:

That is a rectifier diode.

 

Re "replaced my 9V DC PSUs..." - the early machines use a 9V AC power supply so ensure that's what you've replaced it with and that it can also match the current requirements.

yep, typo. edited.

[Mazzspeed]

18 minutes ago, Zarxx said:

I replaced all my 9v AC psu with modern ones several months ago and not have any issues.

May I ask, did you replace the old PSU's with modern switch mode PSU's? If so, how well do they work? Is there any issues as a result of the fact that they're switch mode and not linear PSU's?

[Zarxx]

These are the ones I'm using. From a UK supplier. Again no previous issues with drives and 800. Also have a Stontronics one I've not used.

 

https://www.poweradaptorsuk.co.uk/

 

14 minutes ago, Mazzspeed said:

May I ask, did you replace the old PSU's with modern switch mode PSU's? If so, how well do they work? Is there any issues as a result of the fact that they're switch mode and not linear PSU's?

Not sure if switching as they are still big and heavy.

 

Edited July 31, 2021 by Zarxx

[Rybags]

They don't have any approximated sine-wave crap with modern day AC to AC adaptors, do they?

[Mazzspeed]

1 minute ago, Rybags said:

They don't have any approximated sine-wave crap with modern day AC to AC adaptors, do they?

I honestly don't know, hence why I was asking as I'm imaging that any form of switching may affect the older AC retro machines.

 

I doubt any wall wart would be switch mode.

[Faicuai]

4 hours ago, Zarxx said:

These computers and devices we love are old and you can sometimes have problems, like I just did.

 

 

Those are the main rectifier-bridge diodes on the 800 power-board (which are already quite beefy when compared, for example, with their 400 counterpart). That bridge can handle a good deal of combined power drawn from the -5, +5 and +12v DC "rails" that it feeds.

 

Not just CR206 and CR208 totally EXPLODED there, but only those two, on the right side, which I also find interesting. I have multiple 800 power-boards here, from new to pretty-used, and I have never seen anything like the above.

 

It looks to me you may have another type of problem, on your end. (NOTE: put those "AC" supplies under the scope and check for both AC and DC readings, and sine-wave, just in case...)

 

[ACML]

Do the new wall wart kind have fuses?  One thing I like about the old CO17945 is that it has a 5 amp fuse that blows if the computer has a short and tends to save the hardware from smoking.  I've had two 400 PWR boards go bad, pop the fuse in the CO17945 quick enough to avoid it getting so hot that you'd get smoke.  I've always understood that the XL DC ingots needed replacing, but the CO17945 9VAC blocks are pretty dependable.

 

Edited July 31, 2021 by ACML

[Zarxx]

1 hour ago, Faicuai said:

 

Those are the main rectifier-bridge diodes on the 800 power-board (which are already quite beefy when compared, for example, with their 400 counterpart). That bridge can handle a good deal of combined power drawn from the -5, +5 and +12v DC "rails" that it feeds.

 

Not just CR206 and CR208 totally EXPLODED there, but only those two, on the right side, which I also find interesting. I have multiple 800 power-boards here, from new to pretty-used, and I have never seen anything like the above.

 

It looks to me you may have another type of problem, on your end.

 

Thanks for the advice. Using the Stontronics psu with the 800 at the moment, I have plenty of the original psu too.

It's out the case and have had it on for a few mins and the diodes are staying cool to the touch on the new power board. It's all very odd, no problems otherwise for years. 800 was on and working fine even with the smoke coming out.

 

58 minutes ago, ACML said:

Do the new wall wart kind have fuses?  One thing I like about the old CO17945 is that it has a 5 amp fuse that blows if the computer has a short and tends to save the hardware from smoking.  I've had two 400 PWR boards go bad, pop the fuse in the CO17945 quick enough to avoid it getting so hot that you'd get smoke.  I've always understood that the XL DC ingots needed replacing, but the CO17945 9VAC blocks are pretty dependable.

 

No idea, although the one I was using was going strong. Only issues versus the original plug-cord-brick-cord design is that these wall wart ones are so big you can plug anything next to it

[TGB1718]

1 hour ago, Faicuai said:

Not just CR206 and CR208 totally EXPLODED there, but only those two, on the right side, which I also find interesting.

You may well find that all the diodes (CR206,07,08 and 09) have failed, if you intend fixing this PSU, it's likely either

C206, C208 or C209 has gone short internally, if they are OK the probably the 7805 regulator.

[Faicuai]

2 hours ago, TGB1718 said:

if they are OK the probably the 7805 regulator.

Then this would be a huge problem, because the auxiliary fuse at the power-block should have gone before the rectifier-bridge and this is clearly not the case.

 

I would recommend suspending use of those power-supplies until checked inside / out, including for safety and circuit protection.

 

The safety fuse will be mandarory when attempting to repair the blown-out power board, anyway (if bad regulator, it will pop it, for sure and will further help diagnosing the board in stages). 

 

[TGB1718]

11 minutes ago, Faicuai said:

Then this would be a huge problem, because the auxiliary fuse at the power-block should have gone before the rectifier-bridge and this is clearly not the case.

 

I would recommend suspending use of those power-supplies until checked inside / out, including for safety and circuit protection.

Good call, probably the fuse has been replaced in the past with a wrong rated fuse

[Gavin1968]

That an easy fix. 

[BillC]

On 7/31/2021 at 4:51 AM, Zarxx said:

Not sure if switching as they are still big and heavy.

No AC to AC power supplies are switching mode, this refers to DC power supplies that switch output power on/off at high frequency to maintain the appropriate DC voltage across the output capacitor. The older type linear regulators acted like variable resistors, dissipating the excess voltage/energy as heat.

[griz]

I'm no pro, but why are you guys referring to them as 'rectifier diodes'? Are they not just regular old diodes used in a rectification circuit?

[Mclaneinc]

Simply because they get called that by people like Farnell.

 

Quote

The 1N4001-T is a Rectifier Diode with moulded plastic case. The rectifier diode has high current capability and low forward voltage drop.

 

[_The Doctor__]

this is actually also because back in the day many germanium crystal diodes were slow to act at higher voltages and currents as well, the diodes would introduce noise and had leakage as the AC passed through and sometimes resonated. Back in the "good old days" these diodes in power supplies could create impulse noise. Capacitors across the diodes helped reduce or eliminate it. The capacitors used were not electrolytic. Modern day diodes generally have these issues and don't need the caps. If such capacitors have never been replaced, then there's a good chance they might be leaking and passing AC to the opposite side of the diodes. If you swap them out, cheap .001 mfd minimum 300V-400V disc ceramic are sometimes subbed in. Faster acting shottkey diodes are the way to go however.

[Editorb]

Maybe this is a good thread for me to query:

 

I recently read that unused electronics have changes to capacitors, and that current "reforms" them or something. But, frighteningly, that applying full current can cause magic smoke.

 

I have Lynx and Nomad that I haven't played for decades. Should I get a fancy contraption to slowly trickle power into them? Or, if I'm not going to play them regularly, is there a benefit to the capacitors to use them annually? Should I rotate my Jaguars periodically, or make sure to break out Genesis and 5200 twice a year to juice up the capacitors?

[_The Doctor__]

Rotation of equipment has worked out the best for most folks I've had the pleasure of sharing the retro hobbies with.