TR4 or TR5?

protek

My issue two gives horizontal bars on bootup. Flicking reset takes it to copyright screen though. I measured voltages and got 4,9V, 11,99V and -4,3V. The -5V rail is bit out of threshold but was it TR4 or TR5 that needs changing?

Funny thing that if I power the Spectrum by plugging the wall wart, it'll give the bars but if I plug the power connector, it'll boot normally. My issue 3 doesn't make any difference whichever I plug.

1024MAK

Have the electrolytic capacitors been renewed?

Mark

balford

I'll second Mark's suggestion - I've seen boards producing out of tolerance -5V, capacitor replacement will sort this out.

In my experience TR4/TR5 are either 100% alive or 100% dead :)

B

protek

Caps I assume to be originals. Visually they look ok. Any place to source axial capacitors? My local store has only radial type.

balford

I use Vishay BC axial components from Farnell. They're a little pricey but if you're going to keep the machine, they're a close enough match to the originals:



B

protek

Thanks!

I think it might be also worth mentioning that there is a buzzing sound, when the Spectrum is powered. Is it the coil?

balford

Again perfectly normal - issue 1 and 2 boards seem to have much louder coils than later machines.

B

Zorn

The voltages you measured suggest TR4 & TR5 are in working order.

The initialisation problem could be caused by a failing C27, so I agree with the advice to replace all of the electrolytic capacitors and this could well bring the -5 V supply rail back to where it should be.

Axial electrolytic capacitors are available, but not very common now. Radial capacitors could be mounted as I demonstrate here: https://www.youtube.com/watch?v=TeCVt2T-YSo

If the noise from the inductor is particularly annoying, giving it a thick coating of varnish or similar might help.

ramsrc

Maplin also still have a reasonable range of Axial Capacitors (Surprisingly!)

www.maplin.co.uk/search?text=axial capacitors

protek

Shame that Maplins doesn't ship outside UK and Ireland.

ramsrc

Ooops - Sorry! I didn't notice that you were outside the UK.

Reichelt will ship to Finland: http://www.reichelt.de

I use them a lot, and they carry a very extensive range of components.

To be honest, I am surprised Maplin don't ship outside of the UK. Particularly in this day and age!

protek

I managed to find the needed axials from a local shop. They have to order them from their supplier but there's no extra cost and I can get them next week.

protek

I got the axial capacitors the other day and I swapped them over. The Spectrum now seems to boot straight into copyright text without having to hit the reset button. The -5 V rail now gives -4,48 V instead of -4,3 V, so there is a slight improvement.

Good thing I got some extras because otherwise I would've run short, if I had just ordered the ones mentioned in the 48k Service Manual.

pkersey

Congratulations!