HP97 The journey begins

[teenix]

(07-21-2019 02:29 PM)mfleming Wrote:  Give it a scrub with a microfiber cloth soaked in 90% IPA. The PCB process can leave behind some contamiate they don't always bother to clean up. Definitely improves my success rate.

I gave a new board a good scrub and seemed better, thanks :-)

(07-22-2019 09:37 AM)Harald Wrote:  Hi Tony,

If you like you can send a kit (I'll pay for it) and I can try assembling. My address has changed and I am not sure if you have the new one already, so please make sure before sending anything...
I had to play with the timing on the display driver as well. I can't remember what I settled on (I could look it up if you like). But the display did not work initially when I triggered the DMA on the clock edge I expected to be correct.

Cheers,
Harald

Hi Harald,

Sorry for delay.

As I am definitely not an electronic engineer, I think I might have bitten off a bit more than I can chew. It "seemed" to work fine with the through hole processors, but now it just won't fire up properly at all. I can get 0.00 on the HP-67 display "sometimes" but it is not reliable any more for reasons that escape me. The software simulates ok, and ran ok previously, but not in this hardware.

It might be poor power supply design, but otherwise I've run out of ideas. Below is a CRO snap shot at power up on the 8V rail which propagates through the other supplies. With a 5V scale, it's showing a 12V negative spike which might initially upset the PICs, not sure. After settling down, the supply rails have very low ripple.

Unfortunately, I'm not really geared up for surface mount development, and it is proving to be costly and time consuming, so not sure if I can continue.

cheers

Tony

Edit: Hmmm, I couldn't resist and had to play some more. I tapped into the code on both processors, and just have a blinking LED working from each. Both perform as I expected after multiple quick or slow power on/off cycles. This would seem to suggest that they are happy working in their surroundings, so it appears maybe some bug has crawled into the code on either or both of them. If so, tracking down a fault with two interacting processors will be a tad difficult.