Zx Spectrum 48k Noise

A place to discuss the ZX80's and ZX81's younger brother - the Sinclair ZX Spectrum
Post Reply
Jacobartaylor
Posts: 5
Joined: Wed Jun 15, 2016 11:34 pm

Zx Spectrum 48k Noise

Post by Jacobartaylor » Wed Jun 15, 2016 11:39 pm

I have recently dusted off my old rubber keyed ZX Spectrum 48k the machine has an issue 2 board with the resistor/ diode timing fix. I have also replaced the capacitors on the board and have converted the machine to output a composite video signal, however when i plug in the machine, i can hear this annoying high pitched whining noise, which sounds almost like coil whine in a modern gpu. I was wondering if this is 1 normal and 2 if there is a way to remove this noise. Cheers

RWAP
Site Admin
Posts: 1231
Joined: Thu May 08, 2008 7:42 am
Location: Stoke-on-Trent, UK
Contact:

Re: Zx Spectrum 48k Noise

Post by RWAP » Thu Jun 16, 2016 7:10 am

It is the oscillator which causes this and may need replacing (assuming it is not your power supply!)

Jacobartaylor
Posts: 5
Joined: Wed Jun 15, 2016 11:34 pm

Re: Zx Spectrum 48k Noise

Post by Jacobartaylor » Thu Jun 16, 2016 8:27 am

Thankyou :) do you know where i can purchase this part? I assume it isnt the power supply as i have 2 sinclair 1400 units and it makes no difference what one i use
Last edited by Jacobartaylor on Thu Jun 16, 2016 8:45 am, edited 1 time in total.

User avatar
Fwapp
Posts: 147
Joined: Mon Jun 01, 2015 9:32 pm

Re: Zx Spectrum 48k Noise

Post by Fwapp » Thu Jun 16, 2016 8:37 am

It just the coil buzzing in the power section and the noise is perfectly normal. It's the highlighted part in the pic below.

Image

There's no point in replacing unless the former is physically broken, but the whining can be reduced in intensity by removing the coil and dipping in varnish or wax a few times, making sure not to get any on the legs - allow to dry before refitting :D
ZX80, ZX81 - 2C158C Bugged Rom iss.1, 2C158C "kludge fix" iss1, 2C184E iss1, 2C210E iss3, US NTSC iss1 "straight traces", US NTSC iss3 TS1000

Jacobartaylor
Posts: 5
Joined: Wed Jun 15, 2016 11:34 pm

Re: Zx Spectrum 48k Noise

Post by Jacobartaylor » Thu Jun 16, 2016 9:08 am

Ok thankyou :) if its normal and safe to use it i think i will leave it as it is, i was mainly concerned about causing damage to my machine if it was faulty, plus i cant seem to find any replacement for the coil online

User avatar
Fwapp
Posts: 147
Joined: Mon Jun 01, 2015 9:32 pm

Re: Zx Spectrum 48k Noise

Post by Fwapp » Thu Jun 16, 2016 9:55 am

One thing to check is that when you replaced the capacitors that you put C46 back in the "wrong" way around - the PCB is marked up incorrectly, so you need to put the -ve lead of the capacitor to the + mark on the pcb.

Check all the voltages as well - 12v, 5v, -5v (easiest on the lower memory chips, IC6-13) - as long as they are there or there about you'll be fine.
ZX80, ZX81 - 2C158C Bugged Rom iss.1, 2C158C "kludge fix" iss1, 2C184E iss1, 2C210E iss3, US NTSC iss1 "straight traces", US NTSC iss3 TS1000

RWAP
Site Admin
Posts: 1231
Joined: Thu May 08, 2008 7:42 am
Location: Stoke-on-Trent, UK
Contact:

Re: Zx Spectrum 48k Noise

Post by RWAP » Thu Jun 16, 2016 11:16 am

RWAP wrote:It is the oscillator which causes this and may need replacing (assuming it is not your power supply!)
Oops - yes, I meant the coil - it was early this morning.... :lol:

User avatar
1024MAK
Posts: 1773
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Zx Spectrum 48k Noise

Post by 1024MAK » Thu Jun 16, 2016 1:24 pm

The coil is actually a small transformer. To generate the +12V regulated and the -5V supplies, the Spectrum uses an early form of DC to DC converter (also known as an inverter). This transformer "coil" is part of this circuit. It switches at high frequency. Which results in the copper wire formed around the core vibrating. It is this vibrating that results in an audio buzz to human ears. In actual fact, for issue 1 and issue 2 boards, it's a good sign that the DC-DC converter is working correctly if you hear the buzz :(

The later issue boards use a simular circuit, but the transformer "coil" makes less noise, as over the life of the production run of the 16k/48k Spectrum, this part of the design had various changes in an effort to improve it.

The only source of replacement transformer "coils" is from dead Spectrum circuit boards. More modern DC-DC converters exist, but fitting them means lots of changes to the circuit board.

Mark

balford
Posts: 100
Joined: Tue Dec 03, 2013 10:20 pm
Location: Dublin, Ireland

Re: Zx Spectrum 48k Noise

Post by balford » Fri Jun 17, 2016 4:41 pm

If the coil is too noisy for your tastes, a little varnish over the windings helps reduce it considerably.

Me, I quite like the buzz :)

B

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest