MacinPosh Posted November 7, 2020 Report Share Posted November 7, 2020 I recently brought my Lisa 2/5 back out of the cupboard to have a tinker during lockdown. Unfortunately after a few minutes the contrast goes very dark and the image starts to shrink on the right hand side. I haven't dared to leave it on long enough for something to go bang... The BU406 is quite hot, but probably within normal limits. Any ideas would be much appreciated I've attached the video board schematic for reference. Quote Link to post Share on other sites
bibilit Posted November 7, 2020 Report Share Posted November 7, 2020 My guess is that capacitors are failing. Quote Link to post Share on other sites
MacinPosh Posted November 7, 2020 Author Report Share Posted November 7, 2020 A very good point, although I went through and recapped it when I first got it in 2018. I don't think they'd wear out that quickly? Quote Link to post Share on other sites
bibilit Posted November 7, 2020 Report Share Posted November 7, 2020 I don’t think so. Bad solder joint or another component going bad ? Quote Link to post Share on other sites
stepleton Posted November 8, 2020 Report Share Posted November 8, 2020 A shot in the dark, but could this be a grounding issue? Did you remember to connect the white ground lead to the tab on the metal "cup" that shields the CRT neck? Is there a chance that this could have come loose when you moved your Lisa in or out of storage? Quote Link to post Share on other sites
MacinPosh Posted November 8, 2020 Author Report Share Posted November 8, 2020 Thanks again for the ideas. I've had the card out a few times to inspect it and always made sure everything was connected back up, but i'll check again. Going on the assumption that as BU406 is hot, maybe something in the Horizontal drive circuit is failing, i.e. Row A of the schematic. I'm definitely not an expert in CRT circuitry/flybacks, if anyone has some insight into this it would be most appreciated. I've started looking at the biasing passives but they've all checked out so far Quote Link to post Share on other sites
lisa2 Posted November 9, 2020 Report Share Posted November 9, 2020 I have worked on dozens of these boards, and the capacitors have never been the problem for me... Try replacing the voltage 7824CT regulator U1 ( at lower right corner of the board ), an indication that this is failing is that the the resistor R1 will be burned/cooked (and should be replaced also). This is a very common fault on these boards as they age. Good luck! Quote Link to post Share on other sites
MacinPosh Posted November 10, 2020 Author Report Share Posted November 10, 2020 Thanks lisa2 I’ll replace these and report back asap. Quote Link to post Share on other sites
sunder Posted November 12, 2020 Report Share Posted November 12, 2020 I've recently noticed that all of my Lisas (Lisae?) are now showing various video symptoms. At least one is a trimpot issue which should be easy to fix. Another the display over time scrunches up at the top, but is otherwise readable and playing with the trimpots doesn't help. Another goes out of focus. So I've also got a bunch to repair. So it seems whatever these issues are, whether capacitor, voltage regulator, or trimpot, or other, this is roughly the lifespan of the analog video boards. I'd like to collect the symptoms and fixes, and catalog these so I can update the lisafaq with them: https://lisafaq.sunder.net/single.html#lisafaq-hw-vid_jumpy Quote Link to post Share on other sites
MacinPosh Posted November 16, 2020 Author Report Share Posted November 16, 2020 I finally got some time to replace R1 and U1. Unfortunately it doesn't seem to have made an improvement Are there any other common problem components I can look into? Quote Link to post Share on other sites
techknight Posted December 7, 2020 Report Share Posted December 7, 2020 you should run the lisa with the analog board exposed. then turn a can of compressed-air upside down and hit each component (after its warmed up) until you find the one that alleviates the symptoms. Quote Link to post Share on other sites
aplmak Posted April 28 Report Share Posted April 28 As I said in another post one Lisa video board I replaced the caps.. still had an issue so I recapped again.. maybe it was a bad replacement cap I don’t know or a solder connection. The video boards can be finicky. I’ve always replaced my trimpots as well... for whatever it’s worth. Hey my friend Techknight btw!!! Quote Link to post Share on other sites
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