Noisy Audio on Taiwanese +2

[Morpheus]

My +2 Grey has always had a loud hum to the sound. I've owned it since the release of 1986.

As you stated, it is possible to hear it working as the screen is being drawn in a BASIC listing, the high pitched whine when enter is pressed and changing colours can make it musical.

Code: Select all

5 LET A=20
10 BORDER 0 : PAPER 0 : CLS : PAUSE A : BORDER 7 : PAPER 7 : CLS : PAUSE A : GOTO 10

and the hum will change frequency when the colour alters. This is through both the RF/TV and the sound out port.
I altered the resistors (as shown above) a few years ago to make the AY louder, but the hum is present.

I always thought that all my Spectrums and Amigas were the same and had that working hum to them regardless of the TVs or monitors that they were connected to.

Thanks for the advice Guys
I have only had this a few weeks and In my haste sold my 48K+ to pay for this one. It seemed like a good Idea as most modern games have a 128K requirement or mode.

I also reverted it back to as it arrived and the fault is there anyway so it arrived with it.

Yeah what you are describing is more indicative of what I seem to have and this +2 is from '86 as well. It seems like one of the "quirks" of using real hardware. The noise is a bit less obtrusive when I choose 48K mode as well so I will just work through the list checking the joints and maybe looking at the decoupling capacitors as I have plenty in my box.

Do you think the Transistors that are the wrong way round could cause this problem???

[1024MAK]

Do you think the Transistors that are the wrong way round could cause this problem???

I suspect they will not be the primary cause. But a transistor operated “in reverse” will generate more noise.
It’s still a good idea to replace them though.

Mark

[Morpheus]

I have been having a go at this +2 this morning. I have replaced some of the decoupling capacitors on the power circuit and fitted a new 7805CV Voltage Regulator and the noise has diminished to the point where I can hear the Beeper sound/music on normal volume levels....

Maybe it was the VR after all, I know the thermal adhesive had deteriorated as the VR was not stuck to the heatsink when I unscrewed it.

[MatGubbins]

+2 Grey issue 3 Z70500 - 8639 date.
Should note that I've also done the transistor mod for composite (unsoldered and replaced TR4, TR5 and TR7 with new from Maplins) and the C31 mod that removes the sound noise from the composite signal. I've not yet done a TEA2000 mod as I don't have the correct parts.

[Ast A. Moore]

What PSU are you using with your +2?

[Ast A. Moore]

I've not yet done a TEA2000 mod as I don't have the correct parts.

You mean the RL filter that removes the yellow/blue tint/shift over composite/RF signal? I decided against it on my Toast Rack. I primarily use the RGB output anyway, but can switch to composite on the TV. This lets me see the “worst-case scenario” for testing purposes. Besides, it’s fun to look at things like this, which take advantage of that particular fault.

[Morpheus]

What PSU are you using with your +2?

I have the original power supply and the noise using that is very bad. I have a new 9V 2A Power Supply and it doesn't look a cheap and nasty one but I could not tell really it's made by someone called Akuru.
I normally use Goodleads as the ones they ship have a ferrite choke fitted to the lead which they reckon helps the noise.

Might get one and send this one back....

[Ast A. Moore]

So, if you use a newer, regulated PSU, does it make a difference noise-wise?

[Morpheus]

So, if you use a newer, regulated PSU, does it make a difference noise-wise?

Yes noise is improved by using modern power supply compared to the old Sinclair/Amstrad one.

I changed some of the ceramic capacitors around the the power in and that helped a little bit as well and also the new 7805 Regulator too.

It's getting better incrementally

BTW this board is marked 86/28 on the back....

There is a Mod under the TEAC2000 with a capacitor and a cut track is that normal ???

[Ast A. Moore]

BTW this board is marked 86/28 on the back

Early July, then.

There is a Mod under the TEAC2000 with a capacitor and a cut track is that normal ???

Could be. I think some of the redesigns were incorporated into the main PCB layout around 86/37 and later boards.