problems with a 48k

a_motorized_peach · January 2015

http://imgur.com/lpGfjik

Hi WOS. Its my first post here. I have know about this site for a quite good time, but didnt had the will to contact you.
I dont know much about computers, nor im a technician. But i think the rf output has a problem. I also heard a high pitched and grainy sound when the spectrum is turned on

I would like to see this machine alive. But i cant do much

balford · January 2015

Welcome, and ouch! That doesn't look good. I suspect a failure of one of the components on the board that creates the various voltages needed to power the machine's memory.

It's fixable, of course :) It just depends whether you're willing to put some time and effort (and a little self education) into it, if not several members here offer a repair service for reasonable money.

As a start, let me point you towards this excellent set of videos by Zorn, a member here.

Let us know what you feel up to trying, and we'll do our best to help!

B

Spirantho · January 2015

That looks like a failure of the voltage transistors, definitely... but what's more worrying is the black border. That implies a toasted CPU or even a dead ULA....

My repair service can be found here, by the way :):
http://www.mutant-caterpillar.co.uk/shop/product_info.php?products_id=3481

gasman · January 2015

a_motorized_peach wrote: »

I also heard a high pitched and grainy sound when the spectrum is turned on

If you're talking about sound from the TV, that's normal. 48K Spectrums don't send their sound output through the TV, and just give you white noise - you're expected to turn the volume to zero.

Spirantho · January 2015

gasman wrote: »

If you're talking about sound from the TV, that's normal. 48K Spectrums don't send their sound output through the TV, and just give you white noise - you're expected to turn the volume to zero.

Also, buzzing from the Spectrum itself is actually a good sign, it normally means the voltage lines are correct, as when the -5V line is gone, the coil no longer hits the resonant frequency, and the machine will go silent. Spectrums should always have a healthy buzz (quietly on later issues, loud on early ones).

1024MAK · January 2015

Spirantho wrote: »

Also, buzzing from the Spectrum itself is actually a good sign, it normally means the voltage lines are correct, as when the -5V line is gone, the coil no longer hits the resonant frequency, and the machine will go silent. Spectrums should always have a healthy buzz (quietly on later issues, loud on early ones).

Except for +2A, +2B or +3 machines (which don't have an inverter circuit, so no coil) :-D

Mark

pmsr · January 2015

Spirantho wrote: »

Also, buzzing from the Spectrum itself is actually a good sign, it normally means the voltage lines are correct, as when the -5V line is gone, the coil no longer hits the resonant frequency, and the machine will go silent. Spectrums should always have a healthy buzz (quietly on later issues, loud on early ones).

Thanks for this info. I always wondered why my issue 2 was buzzing so much compared to my issue 6, and suspected the coil had gone haywire. :p

/Pedro

balford · January 2015

Not much of a surprise that early machines make a lot of noise from the coil - those in issue 1/2 machines look positively agricultural compared to those in later models.

Also, as someone who used to be able to tell if a CRT was on in the house just by the whistle of the flyback transformer, the 128K and grey +2 coils must be pretty well made as I can't hear a thing from them :)

B

a_motorized_peach · January 2015

Well, thanks for the information about the buzzing gasman. I knew that the zx spectrum has a built in speaker, but i didnt remember that it could play the sounds made by games or other programs.

So, its the zx spectrum CPU or motherboard fried? the voltage regulation components could be fine? (Assuming what spirantho said) Should i post a recording of the buzzing sound?

I dont have any technical experience with computers, and very little knowledge about its components. Also, it looks like sending the spectrum offshore for repairs is far from my possibilities now. But thanks for the suggestions and offers.

DEATH · January 2015

A)Test voltages!

B)Make Gasman stop his buzzing by covering him in superglue/nail varnish :)

Spirantho · January 2015

For what it's worth, sending a Spectrum is cheap - they're light. :)
Definitely don't throw it out, though - it can be fixed! :)

balford · January 2015

Might be worth stating where you're based also.

B

a_motorized_peach · January 2015

I live in peru. I dont know how much it would cost to send a zx spectrum to any country in the world (england for example), but i think its beyond my economic posibilities (im 18 and im not the best money saver)

Definitely not going to thrash it, but i was thinking of selling it. But it would be nice to see it working again, and even nicer if i learned to program with it, even a simple circle (thinking which way should i follow in my life. I like computers, but i know very little of them, neither program (dammit))

Sorry if i took some lines to write about some of my feelings in a hardware page

RSwipeCA · January 2015

I understand money is always a problem. For what it's worth, if you can beg or borrow a basic multimeter from someone, and then follow the tips in this video ...

https://www.youtube.com/watch?v=IzgCmldm2H4&list=PL4H3oOJzIQMkKiG94z2x0laC7gqqmwBE8&index=1

... then report back what voltages you get on your RAM chips, and the other measurements included in the video, maybe someone here can point you in the right direction. Maybe a relatively cheap fix, you never know.

I hope you get it fixed! It's a great feeling when you save another one of these fantastic little computers from the grave.

problems with a 48k

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