Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!uw-beaver!milton!gordon From: gordon@milton.acs.washington.edu (Gordon Davisson) Newsgroups: comp.sys.mac.hardware Subject: Re: MacPlus Analog Board Schematic Wanted Message-ID: <2078@milton.acs.washington.edu> Date: 22 Feb 90 07:30:18 GMT References: <8582@pogo.WV.TEK.COM> Reply-To: gordon@milton.acs.washington.edu (Gordon Davisson) Distribution: usa Organization: University of Washington, Seattle Lines: 35 In article <8582@pogo.WV.TEK.COM> kenh@pogo.WV.TEK.COM (Ken Hillen) writes: >The +5 volt power supply on my old MacPlus is starting to act funny. If I >adjust it above ~4.8V the screen blanks and the speaker goes tick-tick-tick. >If I adjust it below ~4.6V the reset generator starts resetting continously >so the speaker goes ding-ding-ding. When I set the voltage to ~4.7V the Mac >will usually boot OK, but due to what appears to be poor regulation it will >occasionally start resetting (ding-ding-ding...) or going overvoltage (tick- >tick-tick...). I would like to get a schematic of this board if anyone has >one so I can attempt repairs. Alternately, does anyone have any suggestions >for fixing this problem? By far the most common cause I see of this problem is a bad connection on the cable from the analog board to the motherboard. You can check this by looking at the +5V supply at the analog board end of the cable (if you count the missing pin as #2, #6 is the +5V line and #7 and #9 are grounds). Some voltage loss across the cable is normal, but it shouldn't be more than 0.2V. Also, try looking at the +12V line, since it's the one that's really regulated (the +5V is scaled off it by the ratio of windings in the transformer secondary). If it looks like this may be the problem, you'll have to clean and respring the contacts in the cable. Just pull the cable completely out, then pull out the contacts on the blue wire (#6, as I said above) (you'll have to use a jeweler's screwdriver or something similar to hold in the catch as you pull). Scrape any dirt or corrosion off the contact, and straighten the bend out slightly (to get more pressure on the contact area). It's a good idea to fix the catches before reinserting the contacts, so they'll stay in. Oh, yeah, and be sure to plug the cable back in... -- Gordon Davisson Westwind Computing (206) 632-8141 4518 University Way NE, Suite 313, Seattle WA 98105