On 21/01/2017 17:30, "dwight" <[email protected]> wrote: > It is possible that it is the phone side of the system that is > hanging it up ( no pun intended ). > A while back, I purchased about 12 broken phone modems for > about $2. I found out that all the boards had suffered lightning > damage. Various parts on each board were blown. There was > no consistency. I believe I recovered about 5 boards by combining > the good parts. > The reason I mention this is that it seems your board has had > more than one part fail. It is possible that it was lightning > damaged. >
I agree, it's also been wet and I don't know if that was pre-failure or just an effect of long term storage. There are also some (I assume) voice components like a -24V regulator (MC79L24A) that aren't getting power, I've just looked at the transformer that feeds it and that doesn't appear to be working. I'll post a separate pic of that. > If so, it could be that one of the chips has sent an interrupt to > the processor but not hand shaking when the processor is > asking for data from the modem. > Just a though. The modem in this case is an SAA5070 "LUCY" chip which I guess I can't easily test or even source a known working spare if it turns out to be faulty :/ Cheers > ________________________________ > From: cctalk <[email protected]> on behalf of Adrian Graham > <[email protected]> > Sent: Saturday, January 21, 2017 8:27:06 AM > To: General Discussion: On-Topic and Off-Topic Posts > Subject: Re: 8085 IO ports > > Back to the Executel after a few days relaxing :) > > On 17/01/2017 20:59, "Tony Duell" <[email protected]> wrote: > >>> Yep, on the left two. I haven't dared to pull them from the board though >>> even though they're socketed. >> >> Do be careful, the substrate is a brittle ceramic material... > > I don't think I'll touch them, they're obviously part of the phone subsystem > and I doubt I'll ever plug it into a phone line - I have several One Per > Desks for that sort of thing if needs be. > >>> be seen on both the built-in TV and my external CUB despite lack of sync is >>> for all intents and purposes random crap which again makes me think >>> something isn't initialising properly. >> >> Yes. It sounds like the processor is not initialising the video system, >> clearing video RAM, etc. >> >> Now either the processor is waiting for an interrupt (but from what)? or >> ir's not running the right code. CPU trouble, ROM troublem, RAM >> trouble, address decoder trouble? > > I remember becoming aware recently that it USED to look like it was reading > all four ROMs but now just pulses ROM1. I'm still chasing down one > particular clock source because there's a flip-flop LS74 that isn't getting > anything at all, it's fed from an LS21 and an LS139 decoder which in turn is > fed by A4 and A5 on the address bus. Having the whole board drawn out with > all its connections is one thing but I need to put it into a logical > schematic order. > >>> I have, a small 16 channel one that's Saleae Logic compatible so I'm slowly >>> learning how to drive that too. I should be able to decode addresses and >>> suchlike using it shouldn't I. >> >> Can you clock the analyser from an external input rather than sampling >> every 10us or whatever? If so, clock it from the Rd/ signal and grab the >> 16 address lines (8 on the processor pins, 8 on an address latch, most >> likely a 74LS373, which you will have to find!). Now you can see the >> sequence of locations that the CPU is reading. Most (but not all) will be >> instructions. Find one, compare with the listing, see if the sequence makes >> sense. > > I can trigger it on the RD signal yes. There's 2 LS373s which both had dead > inputs so I replaced those and made sure the signals were correct at all > outputs. I'll have to lose A15 to latch onto RD (only 16 channels) but I'll > give it a go. > > Cheers! > > -- > Adrian/Witchy > Binary Dinosaurs creator/curator > Www.binarydinosaurs.co.uk - the UK's biggest private home computer > collection? > > -- Adrian/Witchy Binary Dinosaurs creator/curator Www.binarydinosaurs.co.uk - the UK's biggest private home computer collection?
