BBC Model B No2. Will it live again!

[stephen_usher]

Those pins are part of the 16MHz oscillator circuit aren't they.

You don't have a dry joint on the ground or power of that chip do you? What do you get on pin 10?

[rubber_jonnie]

Those pins are part of the 16MHz oscillator circuit aren't they.

You don't have a dry joint on the ground or power of that chip do you? What do you get on pin 10?

Pins 1-6 of IC43 form part of the 16Mhz master clock circuit. Continuity is good all the way through from the 16Mhz oscillator to IC6.

With the clock triggered, the signal at pin 8 of IC6 matches that of pin6 at IC43, bar I can't tell what the frequency is, other than it looks like a very tight sine. Measuring at pins 7-4 of IC6 shows them to be different.

When the clock has been triggered and I'm seeing RAS activity, on pin 10 of IC43, I see the same as on pin 3 of the 6502A, as best as I can tell.

I also see activity on pins 37 & 39 of the 6502A.

BTW there is continuity between pin 11 of IC37 and pin 3 of 6502A. Also, IC 34 has been socketed and replaced and continuity to all pins and their next hop checked.

However, if I power on and leave the clock to it's own devices, then none of the above happens. I get no RAS, and see no signals in any of the places described above, so no CPU clocks either or at any of the pins on IC6.

I then trigger it and they all appear. I can boot touching pin 4/5 of IC43 and it will start with all signals in place.

What it feels like is that I am having to kick off the clock, and when it kicks off, it's running but really slowly. I need to hook it up to a TV and hold the probe on pins 4/5 whilst I boot, see if anything registers.

I was hoping to have picked up another working machine by now for comparison purposes, but I've missed out on about 2 or 3 now because the prices have just got silly. Some more coming up this weekend for me to go for.

[BennehBoy]

Clearly you just need to superglue your fingers to that chip :lol:

[rubber_jonnie]

Clearly you just need to superglue your fingers to that chip :lol:

I'm not allowed superglue and my soldering iron time is limited, due to the burnings.......

:dizzy:

[stephen_usher]

It sounds like IC43, the 74S04, is having "issues".

This is why I asked it touching pin 10 on the chip helps (it's on a different clock line from the video chip) and checking the ground and power to that chip.

[rubber_jonnie]

It sounds like IC43, the 74S04, is having "issues".

This is why I asked it touching pin 10 on the chip helps (it's on a different clock line from the video chip) and checking the ground and power to that chip.

I've already replaced it. I have checked all the continuity between pins and their destinations.It's just decided to revert to doing nothing now and touching the IC43 pi4/5 no longer triggers the clock to start.

Ho Hum

[stephen_usher]

Probably the capacitors then. They're the things, along with the resistors, which set up the resonance.

[Tomswork]

Just a thought maybe you have a corroded solder joint in a via

Tom

[rubber_jonnie]

Probably the capacitors then. They're the things, along with the resistors, which set up the resonance.

They are on order :)

[rubber_jonnie]

Just a thought maybe you have a corroded solder joint in a via

Tom

WhenI replace the caps etc I will check.