TR1 and TR2 replacement

Macc

Can anyone tell me the correct replacement part for these? This is for an Issue 4S btw

Zorn

I believe I've used a BC548/549/550 before. Most small NPN transistors would probably work.

Macc

Thanks Zorn, ive ordered some of these then, should do the trick

Macc

Btw, if anyones got the scheme handy and could check the orientation of these two as I know somewhere else on the board they are a bit different

schombi

On all Issue 3 and 4A boards, I found that TR1 and TR2 face each other, means "round" side faces "round" side resp. the sides with the names on.

Macc

The orientation is printed on the silkscreen of the board but I just wanted to be sure due to another transistor (TR4 I think) having to be fitted the other way round on a 4S if you replaced it

Macc

Ive compared the two transistors, the original ones C945 and the ordered ones BC548B and theres a bit of a difference in various values, are these going to be ok?

Zorn

I'm more-or-less certain the transistors I suggested will work for all NPN transistors in the 16/48K Spectrums, apart from use as TR4 or TR7. The pin-out may not be the same as the originals - I can't remember, you'll have to check datasheets.

Macc

Had a good look and it appears the orientation is the same, the EBC positioning on both transistors is the same so common sense that they fit the same. Should be here tomorrow so ill fit and see.

Btw, replacing R53 (300ohm) resisistor with an 82ohm, would that help with the black and white (sometimes colour) problem I have with this board and the 2+v Im getting on the video in?

Macc

Ok, transistors arrived today, replaced them and tried it, very, very faint picture, voltage on video in now down to 0.7v

Macc

The transistors needed to be fitted the opposite to what the silkscreen tells you (I just knew it would be something like that, hence me asking first)