CBM 8032, nothing on screen

No, the cable just was off.. and I happened to look up and saw that single dot there. It vanished after a while. I don't have an oscilloscope (yet) but I do have a multimeter and will try what you suggested. I'm curious.. to what extent can you 'piggyback' good ram on top of bad, or chips, for that matter? I was introduced to that trick on my 4016.. I piggybacked a 2114 on the first 2114 video RAM and everything started working again. Can you do that with any suspected bad chip? Can you do it with all of them at once? (I have a very large lot of Commodore/MOS/TI chips and have tons of 4116s and 2114s, mostly known good. And can you do piggybacking with ROMs? I've swapped out all socketed chips but haven't attempted anything with the soldered ones. I did try experimenting with the 2114 piggyback trick, and tried it a bit with the 4116. Every now and again with the 4116s, I would place the chip over an existing one, turn the PET on, and get no chirp. On one chip, about four down from the back, I got the chirp followed by a high pitched squeal. I have tried some tricks with the keyboard to see if this is purely a video problem or if there's something going on with the ROMs.. I did a PRINT CHR$(7) -- no beep. Tried holding down the keyboard for a long time.. nothing there either. Brad Hodge Better Computing Tel: 604.892.1224?? Fax: 604.898.3155 brad at bettercomputing.net www.bettercomputing.net ? -----Original Message----- From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org] On Behalf Of Tony Duell Sent: Saturday, January 25, 2014 11:55 AM To: cctalk at classiccmp.org Subject: Re: CBM 8032, nothing on screen startup. THat last sentence is ambiguous. Do you mean that if you pull the cable off once the machine is running youy get a dot on the screen (and does it remain or fade out?) or do you mwean that you get a dot i nthe middle of the screen if you power the machine up with the video cable unplugged for mthe motherboard? If the latter, or if the dot doesn't fade out, I am totally puzzled... Anyway, here's hwat I would do... Firstly, determine if the problem is in the monitor or motherboard. There are, IIRC, 3 TTL level signals from the motehrboard ot monitor. Horizontal drive, Verticla Sync, and Video. Check them witha logic proble (much better than a 'scope here, IMHO, at least to start with, since what you are really looking for is signals that are stuck in one state). If the video signa lis never being assettedm, the screen will be blank (it should be!) but no amount of wortk o nthe monitor wil lget it going. Assuming the motherboard is outputting video, the quickest thign to do is to measure the CRT pin votlages. IIRC, tue PETs use a 7 pin (modified B7G) based CRT> The pinout is (at least for every such CRT I've seen) : 1 Control Grid 2 Cathode 3 HEater 4 HEater 5 Control Grid 6 First anode 7 Second Andoe (focus) One of pins 3,4 is likely to be ground. Expect about 11.5V-12V on the other one. Expect a few hundred V o nthe 2 anodes, about 40V-70V on the cathode, and ratehr less (may even be -ve) on the control grid. Ifd all the higher voltages are misisng, suspect problems in the horizotnal section (these voltages come form the flyback transformer), but as you can get a dot on the screen, this is unlikely. If one is missing, uspect the associateed rectifier/capacitor. Anotehr thing that will remove the display is to great a -ve bis o nthecotnrol grid. That is, the grid is too low in voltage _or the cathode too high_. It might be aproblem with the video output transistor or something. -tony