464 will not load

[YRep]

Hi all, first time poster here.


Got a 464 that will not load here. Using CTRL+ENTER to get play prompt, then pressing play, the tape will tension up, press any key and the command prompt resets. Have checked inside and deck seems mechanically fine. Can anyone offer any advice please?

[Bryce]

How do you mean "the prompt resets", does the whole computer reset?

Bryce.

[YRep]

Hi Bryce


That's exactly it - the whole machine resets, the screen flickers and then I'm presented with the 'Ready' prompt.


Thanks for your reply!

[Bryce]

Sounds like there's a short circuit in the tape drive. This could be one of the many loose wires that has grounded to the tape drives frame or it could be somewhere inside the motor itself.

Bryce.

[YRep]

Alright!  I'll take a look inside and see what I can discover (if anything!)  I don't suppose you have a schematic/circuit diagram to hand?  Of course I'll look for one if I need to, but I thought to familiarise myself before I take the 464 apart.


Thanks again.

[Bryce]

All you need can be found here: Service Manuals - CPCWiki

Bryce.

[CPC_Fan]

Hi and welcome to the forum YRep. Sorry I can't help with your tape loading problem, but you have definitely come to the right place for help and advice. It sounds like you have some knowledge about electronics in general, so I am sure that with the aid of the service manuals that Bryce put up a link to and the electronic/hardware experts on here, you will get it fixed.

[leon]

thank you.
found the fault and now working!! it was just the wrong power supply they have given us it with 6v 200ma, used 5v2a and all is well

[CPC_Fan]

Good news.

[Bryce]

Be glad that the 6V PSU was only able to supply 200mA, if it had been 6V 2A you would have had a fried/dead CPC!

Bryce.

[TFM]

Really? By only 1 Volt too much already? 

[Bryce]

Most TTL chips will already die at 5.4V ! They are ok up to about 5.25, but everything above that really is playing with fire.
On other computers the voltage may not be critical, because the computer regulates the voltage internally, but the CPC has all the regulation in the monitor, so using an alternative PSU means that you are directly supplying the chips and have to keep the voltage as close as possible to 5V.

Bryce.

Edit: This is why I don't recommend switch-mode PSUs on the CPC. It means that there is no linear regulation at all, and not all ICs get on well with a pure switch-mode supply. On computers with internal linear regulation switch-mode isn't as big an issue.

[Tai]

Edit: This is why I don't recommend switch-mode PSUs on the CPC. It means that there is no linear regulation at all, and not all ICs get on well with a pure switch-mode supply. On computers with internal linear regulation switch-mode isn't as big an issue.

Then using a PC PSU to power the Amstrad CPC could be dangerous?

[Bryce]

It depends on the PC PSU. The good ones are extremely well regulated and don't budge from 5V even if the input voltage is all over the place and also don't cause spikes when turned on. Using a cheap old PC PSU could damage the CPC in some situations. The biggest problem with PC PSUs is that they can supply massive amounts of amps, so if something does go wrong, it has the power to completely fry the CPC. If a cheap small 2A PSU gets overloaded from a short or whatever, they go up to 2A but then the voltage starts dropping, minimising the damage they can cause. The PC PSU will supply a lot more amps at 5V before it shuts down, potentially frying tracks / PCB / wires etc.

Bryce.

[Tai]

I've been using an old PC psu for my CPCs for years and nothing bad happened.
However, considering what you said, I'm going to use an AC/DC adapter (5V 2A) just for peace of mind.


Thank you Bryce.

[pelrun]

Or you could just add a fuse...

[Bryce]

For obvious reasons (the fact that I do a lot of hardware experiments on my CPC), I use a Spectrum +3 PSU to power my CPC... Because it's fully fused.

Bryce.