Fixing a Sinclair Spectrum 128k +2A/B Power Supply (PSU) - Common Cause of Failure

[@GadgetUK164]

Great stuff - first time I've seen the insides of that particular PSU.

[@peddersoldchap]

there are no videos of the grey +2 PSU hint hint ;) ;)

[@VintageTechRepairs]

Nice easy fix, Glad to see all is well

[@richardpowell8198]

Hi mark great video! I`ve got a +3 power supply thats causing a slight grain to my out put, but when I use my +2 power its nice and bright and clear any idea??

[@MarkFixesStuff]

Hi Richard. The capacitors are likely dried up inside. I'd recommend servicing it with new ones because they won't be smoothing the power properly anymore.

[@Rockythefishman]

Nice video Mark, I must be getting told we got taught how to wire a plug at high school !!

[@MarkFixesStuff]

+Rockythefishman Same. In science class.

[@kakabixlis]

Good show mate !!hope this AC will work properly :)

[@trojan20112011]

common causes of failure also includes,regulator and resistor failure on the -12 volts side of the supply after it was run under load when the fuse blew.(they literally burn out) 5 volt can also fail at the power transistor,as it regulated from the +12 volt side which can also fail these were also made with no mains fuse slung over the heatsink,i have a few,just another variant made by amstrad

[@davidsmethurst1056]

I've repaired a few of these power supplies where the mains fuse (upside down) has been a T3.15 amp fuse rather than T315mA. As they still had a tie wrap around them they must have been like that from the factory! Needless to say, I installed the correct value fuse before I boxed them up. Looking at the size of the wire inside the fuse on this one, I'd say it's also got the wrong size fuse fitted. You might want to pop it out and check...

[@MarkFixesStuff]

I'll be honest. I don't actually use these myself. I have a new more efficient PSU for my DIN plug powered Spectrums from ByteDelight. I'll pop a video up about it soon. Noted on the wrong fuses from the factory. I've found one similar as well. Fairly typical QA for the time.

[@davidsmethurst1056]

@@MarkFixesStuff Agreed on the poor QA. A 315ma fuse would probably stop the thing going up in flames if the transformer developed a short in the primary winding - a 3.15A fuse definitely wouldn't 🙄 It does make me wonder why they were not subject to a recall.....

[@MarkFixesStuff]

@@davidsmethurst1056 "money"

[@davidsmethurst1056]

@@MarkFixesStuff Of course, this is Amstrad we're talking about 🤣

[@stuartmcfarlane213]

Mark, what circuit is the 3.1 amp fuse on? Mine has blown and I'm trying to work out which component might have caused it to blow.

[@blackterminal]

Thanks for the video.

[@Tetlee]

I recently blew my +2a by unplugging and plugging back in a divmmc device from the back, stupidly without powering down. Is there a slim chance its this fuse that is blown? I know likely more serious than that.

[@chris-ip4pk]

Mark was was the fault on the rubber key speccy power supply ,hence the recall.i know the hazard but what was the actual fault.

[@MarkFixesStuff]

It was the cabling I believe. The strain relief was inadequate.

[@bobbus_74]

Re-watching this in 2023 for no reason other than why not?

[@StephenBlower]

No part number? I've checked the data sheet and these match at CPD by Multicomp. These are the cheapests ones: Fuse, 5mm x 20mm, Glass, Quick Blow, 3.15A 3.15 A 250 v = MC000829 Fuse, 5mm x 20mm, Glass, Quick Blow, 315mA 315 mA 250 v = MC000892 Is using the cheapest ones OK or not OK?

[@MarkFixesStuff]

Stephen Blower thanks for the info! Never had an issue using cheaper fuses to my knowledge. They are not complex parts so doubt it would be a problem.

[@christhacker4900]

Excellent vid mark, now how similar are they to the modulators on the Amstrad cpc range?

[@MarkFixesStuff]

To be honest I don't know as I use RGB to SCART cables on my CPC, so haven't looked inside an MP1 or MP2!

[@RUTGERMORTENSEN]

Awesome thanks forbthis video very helpful

[@paulisthebest3uk]

Really good video enjoyed it

[@MarkFixesStuff]

+paulisthebest3uk Cheers Paul mate!

[@blackterminal]

Be careful what you put in the dishwasher. I had some black plastic become discolored.

[@GazzJ82]

Just note, most plugs back then didn't have sleeved live and neutral pins like they do now.

[@reddragon27284]

If you do make a video about fitting plugs it might be worth pointing out that a 13A fuse is not appropriate for this kind of equipment.

[@MarkFixesStuff]

+RedDragonUKTech I was thinking that at the time actually, but was trying to be concise (hence just "moving on") and didn't want to end up rambling and ranting. I will add it to the list though as it's a good point and very well made.

[@Jenny_Digital]

Hi Mark, I did a full reverse engineer and theory of operation on one of these power supplies (Not on KZbin, I don't even have a decent camera) having repaired a good few of them. Can you spot the design flaws In my favourite Speccy's brick? Oh and I still have some of the files if anyone wants them.

[@MarkFixesStuff]

Hi Duncan,. That sounds really useful. If you are on facebook you might want to join our group Spectrum For Everyone at facebook.com/groups/spectrumforeveryone/ where loads of us would welcome you and your research!

[@Jenny_Digital]

Mark Fixes Stuff - Retro Console and Computer Repairs, Reviews and MORE! So, I'm not on Facebook on a matter of principle since around 2012 but I am signed up to World of Spectrum and I do use Google+. Maybe one of these platforms might be of value.

[@BenRattigan]

Just opened mine up, it doesn't have the second fuse or mounting. is labelled as +2A PSU

[@MarkFixesStuff]

I'd like to see a picture of the insides if possible

[@BenRattigan]

@@MarkFixesStuff photos.app.goo.gl/d8oLaHBywVTgzZWdA Was hoping there was something obviously wrong with it as 5v pin reads around 2v

[@MarkFixesStuff]

@@BenRattigan I'm not very familiar with that model of PSU. If I were looking to fix this I'd start with voltages inside the PSU, but at your own risk :P I suspect that one of those TO-220 packages is a 7805? If so, check that it is getting more than 7.5v on the input leg and is outputting 5v on the output leg. Capacitors are always suspect after 30 years as well.

[@BenRattigan]

@@MarkFixesStuff Yeah I am gonna put to onside for now managed to get hold of another couple of them to try on my +2.

[@BenRattigan]

@@MarkFixesStuff Thanks

[@Millay2006]

You forgot to mention it should be a 3amp fuse not a 13 amp, if my maths is correct :)

[@GadgetUK164]

+Andrew Millea Yes, 13 amp is a fire risk in something like that!

[@MarkFixesStuff]

+Andrew Millea As I said to someone else, that's absolutely correct but to keep the video short and I decided to leave that for a more general video. That plug is in the bin now. 3a for sure by the way, and BONUS points for saying "maths" instead of "math"!

[@GadgetUK164]

I was sure you would already know that =) I just figured you forgot to mention it. I forget to mention lots of things in my vids as well. It's easily done when your brain is rail roading you into thinking talking about other parts of a system etc. =D

[@davidsmethurst1056]

@@GadgetUK164 Yes, even more so when the wrong mains fuse was fitted inside the PSU!

[@tonycampbell1178]

Wrong fuse in the original plug

[@MarkFixesStuff]

It often is. This one got past me. I’m going to do a video soon about checking plugs, picking an appropriate fuse and making sure the whole shebang is safe.

[@memsom]

Worth noting that that is a +2A/+2B PSU. The +2 had a completely different PSU that was more similar to the legacy Sinclair models.

[@MarkFixesStuff]

+m4tt3m50n Cheers, I hadn't realised that I had not put the A in the title. I show the DIN connector in the video so that should be enough to differentiate it from the grey's PSU. Edited!

[@keiranbowes1979]

You know your doing well when you get complaints from sex workers.

[@MarkFixesStuff]

+keiran bowes I know right!!!!!