More Serial Woes

[t0nyt]

Many thanks Martyn/Pr0f

Have finally located the ICs on the mobo, not sure why I couldn’t see them before!

Have ordered some to try

Many thanks
Tony

[Pr0f]

On the issue 6 board - this is to the left of and down a bit from the loudspeaker connectors - which are under the large heatsink (when viewing from the front of the machine)

https://www.sinclairql.net/srv/QLPCBoardIssue6.gif

[t0nyt]

I'd forgotten that that 12v power-line is also fed out both SERial sockets, albeit with a series 680ohm resistor to limit the current-draw. You'd have to be quite unlucky to pop the 78L12 by mis-connecting that 12v line at the SERial port (even shorted to GND, the series resistor would limit current to 12/680 < 20mA.)

I definitely didn't mis-connect anything at the serial port

Just so I'm 100% sure what I'm doing, it's the IC37 (by leg of large capacitor) that I'm replacing with a 78L12, +12v 100mA regulator please?

Many thanks

[Maskenlos]

Is TR10 missing by purpose?

[t0nyt]

Is TR10 missing by purpose?

Don’t know. This isn’t a picture of the actual QL I’m trying to fix, it’s my spare parts board which had a memory problem I couldn’t find a fix for. I didn’t remove TR10 from it though.

[Martin_Head]

While you are changing the the plus and minus 12 volt regulators. I would also replace the electrolytic capacitors involved in the two supply rails.

C37/C39 470uF 25v, and C38/C40 47uF 15v (I think that's the correct references, the circuit diagram I looked at is not very clear)

The caps are 40 years old, and may have started to dry up.

[t0nyt]

While you are changing the the plus and minus 12 volt regulators. I would also replace the electrolytic capacitors involved in the two supply rails.

C37/C39 470uF 25v, and C38/C40 47uF 15v (I think that's the correct references, the circuit diagram I looked at is not very clear)

The caps are 40 years old, and may have started to dry up.

Ok, many thanks

[Pr0f]

I'd forgotten that that 12v power-line is also fed out both SERial sockets, albeit with a series 680ohm resistor to limit the current-draw. You'd have to be quite unlucky to pop the 78L12 by mis-connecting that 12v line at the SERial port (even shorted to GND, the series resistor would limit current to 12/680 < 20mA.)

I definitely didn't mis-connect anything at the serial port

Just so I'm 100% sure what I'm doing, it's the IC37 (by leg of large capacitor) that I'm replacing with a 78L12, +12v 100mA regulator please?


IMG_4243.jpeg


Many thanks

That's an early issue 5 - as you still have the battery contact points (not ever properly implemented)

But yes - that's the 12V regulator

[t0nyt]

Thanks for all the help and advise on this one, much appreciated

Spare parts arrived but I haven't been able to get it working and have therefore decided it's time for it to go to the great spares box in the sky (and I can't face any more soldering)

Will re-use the MDV1 as MDV2 in my other spare QL and bag all the other parts up for my spares box

Many thanks