Quadra 605 boot problems

[jch]

I‘ve got Quadra 605 with motherboard 820-0364-A, and ASTEC AA16251 power supply. I’ve recapped both of these using caps from Console5. The motherboard caps definitely needed replacing and did cause some damage to the -5V trace near C36, which I repaired with a bodge wire going to the -5V connection on the bottom of the board. I was able to verify connectivity to the following -5V pins:

• U30 DFAC-II pins 6, 5, 15
• U21 26LS30 pin 10
• U22 26LS30 pin 10

When I attempted to boot the machine without HD/Floppy connected, and no 3.6V PRAM battery, I get a boot chime followed by the sad mac tone and no video. I’ve got a DB-15 to VGA dongle with settings for 640x480 video, which i know works or other machines like my IIsi.

I’ve read that not having a battery can cause the no video problem, and since I did not have a good battery on hand I attempted to use 9V to 3.3 V power converter to see if that would fix the no video issue (without success). I realize its not quite 3.6 V but assumed it would be close enough. I’ll get a proper battery soon to rule this out. I’ve also tried the power ”on/off/on” trick to work around the no video problem too.

I’ve verified the that the power supply is providing -5V, +5V, +12V. I’ve reseated the RAM and Video RAM, but have not attempted to use Deoxit 5 on those connectors.

Any ideas on what I can probe to see what’s causing the sad mac chime? Best I have is a voltmeter, so I‘ll be limited in what I can check.

 

[croissantking]

While a missing battery can prevent boot, it shouldn’t cause Sad Mac tones. And you say you’ve tried the on/off/on trick so it’ll be something else (bad RAM, maybe?)

 

[jch]

I’ve been able to at least identify that the slotted RAM causes sad Mac chimes. Since the motherboard has its own RAM, removing the stick of RAM makes the sad Mac chime go away. I still don’t have any video. I do have another Quadra 605 that I can see if swapping VRAM makes the video work to rule out bad VRAM. I was a bit concerned that some other problem (e.g. short) might screw up other potentially working VRAM by putting it into the machine without doing some form of checking before doing so.

Since I wrote my original post I created a USB/serial port cable and can run the Tech Step diagnostic commands. Still learning what it’s capable of doing. i am rewatching Adrian’s Digital Basement videos to glean useful ideas for commands to run to narrow down the issues. I also purchased a FNIRSI 2C53T handheld oscilloscope to better check the board for signals. Open to suggestions for investigating the video circuitry.