On Oct 14, 2013, at 8:30 PM, Liam Proven wrote: I have a few books on troubleshooting old Macs from 128K to SE. I'll be glad to scan a few pages if necessary. However, the birds-eye view would say that it's either the CRT or something in the analog board; my guess is the analog board, though transatlantic prognostication without any low-level detail is necessarily an inexact thing. :-) In either case, the analog board is more likely (in my recollection) to go bad, and it supplies both the video signal and the power supply to the CRT. It also supplies the power to the logic board, so it's obviously not TOTALLY gone. But it could easily be something in the HV supply or the logic chain. Do you have meters and/or oscilloscopes to determine potential problems? I assume you've osmosed enough of the general warnings about CRTs and HV supplies from this list to know that you should take at least some basic precautions when poking around inside. - Dave

On 10/14/2013 07:30 PM, Liam Proven wrote: I assume you've checked the obvious: the brightness control under the screen? :-)

FWIW, the Mac+ will boot without a mouse. I can't remember if it needs a keyboard, soemthign tells me it doens't OK... OK... Possibly not a lot. The Mac+ is on 2 main PCBs. One is flat at the bottom of the case and is claled the 'digitial board' by Apple. It contains the CPU, RAM, ROM, all the digital stuff, basically. The other is vertical at the left side of the case. It's the 'analog board'. It cotnains the switch-mode PSU and the CRT driver circuits. For the machine to do waht it's doing, the PSU must be basically working. Maybe the 12V supply could be missing or low, that is the one used to power the monitor circuitry. The monitor circuit is pretty conventional, fromwhat I remember, but I suspect that's not a lot of ohelp to you. I cna tell you how I'd troubleshoot it : 1) Take off the case. Power up 2) Look to see if the CRT heater is glowing. If so, the 12V line is present, and the picofuse in the supply to the monitor (a soldered-in fuse, looks abit like a small resistor, on the analog oboard) is OK. 3) Cheakc all PSU outptu votages at the connector to the digital PCB 4) If the picofuse ahs blown, then I would suspect horizontal output toruble,m and would check the transistor for short circuits. Then sort otu that area 5) If the fuse is OK, then check all the CRT electrode voltages. I can't rememeebr if the CRT base is connected ot the PCB by oen fo thpse 0.156" conenctors. If so, I'd check there. Also check the EHT at the anode conenctor. Hopefully this will show up a problem, like the electron gun being biased way beyond cut-off (grid very -ve wrt the cathode) or a missing anode votlage. Again, if all CRT electode votlages are very low, I'd suspect horizotnal output trouble. THe first problem is getting the case off. It's held on by 5 screws. 2 are easy, at the neds of the connector panel. One is inside thge battery cover, and is easy to get to when you unclip the cover. The last 2 are inside the handle at the top. Most normal Torx drivers 9for all these screws are TX15 heads) will not go in. You need a very long one. Do you have that? If you do open the case, be careful. There are lethal voltages o nthe analog board. The monitor voltaesg are bad enough (IIRC there's around 800V on one of the CRT base pins). But there's also rectified mains for the SMPSU. which is much more dangerous. So take great care. Checki nthat the CRT heater glows is a good fisrst step, and is relatively safe and doesn't need instrumennts. Look into the back end of the CRT and see if you can see an orange glow. After that, if you have a voltmeter (up to about 1000V) and are prepared to make some measurements, I can look up the connections to the CRT. -tony