Quadra 650 - Not Booting but PSU works

[pdyholman]

Hi Everyone,

Like many of you, I'm trying to bring life back to a Quadra 650. It was working fine the last time I booted it up, around 5 years ago, and unfortunately no signs of life when I brought out of storage a few weeks ago and plugged it back in.

I took it apart and blew out the dust, replaced the PRAM battery (no damage from previous one), everything looks in good condition. Shorting pins 9 and 10 on the PSU powered up the fan. Voltage levels on all the PSU pins look OK-ish (slightly off 5v/12v etc).

With the hard disk, floppy, CD unplugged and case open, when I hit the "on button" on the keyboard, I can hear a little "tap-tap-tap-tap" from the PSU, suggesting its a problem with the trickle voltage and the soft-power on.

Does any one know an an easy way to over-ride the keyboard based mechanism (even temporarily), so that I can see if the system can boot up (to test the hard disk etc.) ?

(Or any other suggestions)

I couldn't see an easy way to safely short pins 9 and 10 when putting back the PSU (worried that one end of the "short" wire might pop out). I looked briefly at taking apart of the PSU, but a bit worried I couldn't put it back together ! (Would be great if I could find a 10 pin molex extension capable!)

(Unfortunately, a question unanswered in https://68kmla.org/bb/index.php?threads/quadra-650-dead-but-psu-works.39020/)

Many thanks,

Paul

 

[Hollie]

Hey Paul,

Have a look at the power button on the back panel next to the video output port. If it's stuck in, rotate it 90 degrees with a fingernail and it should pop out again. This'll let you fire up the machine without a keyboard attached.

 

[pdyholman]

Thanks Paulie ! Unfortunately (and apologies, I should have mentioned this) - pressing this button also only yields the slightly "tap tap tap" noise of something trying to start !

 

[joshc]

Sounds like a bad power supply to me. Do you have another you can test with?

 

[Phipli]

I can hear a little "tap-tap-tap-tap"

This could be a short, depending on what exact noise you mean. The PSUs reset themselves if there is a short. As the 650 has tantalum capacitors, the first think I'd do is look at each one (usually yellow cuboids) and see if any have burn marks or a brown dot on them. Share a photo if they do.

 

[cheesestraws]

Yeah, check the capacitors (generally labelled Cx on the board) for burn marks, but there are other reasons that the PSU wouldn't start as well. Generally I've found the PSUs in those machines more inclined to disintegrate than the logic board capacitors, at least so far, but either's possible.

Also amused at the UK 650 fan club descending on this thread en masse. Hi, folks...

 

[joshc]

Wombat army assemble

 

[pdyholman]

Very grateful for all assistance !

@joshc : unfortunately, this is my only Mac of this era (no spare PSUs). I'd hope that by being to show that the fan was working (and pins all having the expected voltage) it would be enough to fire up the machine.
@cheesestraws , @Phipli : capacitors on the motherboard all look OK (photo)

I'm aware that PSU's are the achilles heel for this era of computer (for my BBC Micro, rather than recapping I opted for a modern replacement PSU), so if the motherboard etc was functionally, I was already thinking of following Eric Bylenga's guide to modifying a suitable ATX - but would be rather annoying if I did this and found that the logic board was the culprit !

(Confession: the reason why I went into software development in the first place is because I find soldering more stressful than coding, where its easier to revert to a previous version!!)

 

[Phipli]

Wombat army assemble

Yeah, check the capacitors (generally labelled Cx on the board) for burn marks, but there are other reasons that the PSU wouldn't start as well. Generally I've found the PSUs in those machines more inclined to disintegrate than the logic board capacitors, at least so far, but either's possible.

Also amused at the UK 650 fan club descending on this thread en masse. Hi, folks...

PowerPro to the People.

 

[Phipli]

Very grateful for all assistance !

@joshc : unfortunately, this is my only Mac of this era (no spare PSUs). I'd hope that by being to show that the fan was working (and pins all having the expected voltage) it would be enough to fire up the machine.
@cheesestraws , @Phipli : capacitors on the motherboard all look OK (photo)

I'm aware that PSU's are the achilles heel for this era of computer (for my BBC Micro, rather than recapping I opted for a modern replacement PSU), so if the motherboard etc was functionally, I was already thinking of following Eric Bylenga's guide to modifying a suitable ATX - but would be rather annoying if I did this and found that the logic board was the culprit !

(Confession: the reason why I went into software development in the first place is because I find soldering more stressful than coding, where its easier to revert to a previous version!!)

View attachment 52618

I recapped my Beeb PSUs, although I never finished after I misplaced the caps

Can you record the tick tick tick sound? It would help me know if it is a short. But don't leave it doing it too long, because it might be a short :s

Is there any chance some metallic detritus has fallen onto the circuit somewhere? Do any other components look like they got toasty?

unfortunately, this is my only Mac of this era (no spare PSUs

You are going to have to get yourself a IIci and a PM 7100. It is clearly the only way you can do a full set of tests. Perfect excuse. Absolutely mandatory I'd say.

 

[joshc]

You are going to have to get yourself a IIci and a PM 7100. It is clearly the only way you can do a full set of tests. Perfect excuse. Absolutely mandatory I'd say.

I fully agree. Buying more Macs is the best way of saving this one. Everyone needs at least two 650s anyway.

 

[cheesestraws]

unfortunately, this is my only Mac of this era (no spare PSUs).

If you're in Bath as your profile says, I can lend you a known-working 650 PSU, I'm only a handful of stops down the train line from you, and I go through Bath often on my way to Wales.

 

[pdyholman]

Hi Everyone,

Re more Mac's - couldn't agree more (perhaps I shouldn't mention on this 68k forum, that I have an M2 Mini on order ...)

> I recapped my Beeb PSUs, although I never finished after I misplaced the caps
Ha! I actually have a second Beeb (the first was one was bought from my University when they upgraded - I was promoted to get it working because I realised the contents of my 5.25" floppies [and indeed the drive] would be slowly decaying, the second a more recent gift) with some capacitors I plan to fit when I next have time to solder ...

(I was hoping the 650's titanium caps would save me from dealing with dying caps !)

> Can you record the tick tick tick sound? It would help me know if it is a short. But don't leave it doing it too long, because it might be a short :s

OK, will do on Friday (business trip this week). Only happens when (and for a second after) the keyboard/rear "on" button is pressed).

> Is there any chance some metallic detritus has fallen onto the circuit somewhere? Do any other components look like they got toasty?

Don't think so, motherboard looked clean enough, and I gave it a good blow with compressed air to clean away dust. However, will have a more detailed and methodical check ...

 

[3lectr1cPPC]

You can check with a multimeter in continuity mode whether any of the tantalums are shorted. If you put the probes on the positive and negative points and you hear a beep, it’s shorted.

 

[Phipli]

You can check with a multimeter in continuity mode whether any of the tantalums are shorted. If you put the probes on the positive and negative points and you hear a beep, it’s shorted.

Just to be clear, if you hear a sustained beep its shorted. Sometimes multimeters beep with caps as they're charging or discharging from somewhere else.

 

[3lectr1cPPC]

Ah yes, right.

 

[Hollie]

Yeah, the Astec/Delta PSUs in these things are hit or miss at this age. You'll either be lucky and get a working one, or it'll be dead. Or extremely unlucky and it'll explode whilst in use. Although at this point that happening means you'll join the club.

The Quadra 650 and 800 boards are notoriously reliable because of their use of non-leaky capacitors. Usually the only thing that stops these things working is the power supply. There is a UK Q650 fan club for a reason...

 

[pdyholman]

Hi Everyone,

As an update, I took apart the upper chassis, removing all the cables and had a more thorough visual inspection (and dust removal) All looks good.

As suggested, I've made a short video of my next test :

Added the PSU, pushed rear button - and clicking still present. However, I left the PSU in for a few seconds (rear button no longer depressed) and noticed a different pattern of clicking.

I'm not an electrical expert, but feels like a defective PSU. (When I get more time, I'll work out if my multimeter will offer continuity mode!)

 

[pdyholman]

As an update, my plan is to move using an ATX PSU, with the help of Phipli and Lee.

However, whilst waiting, I thought I would verify that the logic board is at least working, by cutting an ATX Molex from a dead PSU to size and using @Paulie's approach to map wires from another (working) ATX PSU into the Quadra configuration.

Referencing https://bylenga.ddns.net/index.php?page=Centris_ATX.php for final checks on voltages for each pin before plugging into the quadra.

(The only change I made was to connect have ATX-17 go into Q-6, with ATX-14 connected separately to a spare ATX ground).

Well, clearly I have made a newbie mistake (or there was an electrical short on the logic board that I missed), and now have to summon up the courage to replace C40 ... :-(

 

[Phipli]

As an update, my plan is to move using an ATX PSU, with the help of Phipli and Lee.

However, whilst waiting, I thought I would verify that the logic board is at least working, by cutting an ATX Molex from a dead PSU to size and using @Paulie's approach to map wires from another (working) ATX PSU into the Quadra configuration.

Referencing https://bylenga.ddns.net/index.php?page=Centris_ATX.php for final checks on voltages for each pin before plugging into the quadra.

(The only change I made was to connect have ATX-17 go into Q-6, with ATX-14 connected separately to a spare ATX ground).

Well, clearly I have made a newbie mistake (or there was an electrical short on the logic board that I missed), and now have to summon up the courage to replace C40 ... :-(

View attachment 53582View attachment 53583

What voltage rating was the cap you used on C40? What voltage is C40 going to see? You can check continuity from the power molex to the pads.