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| LC 475 chimes but no video output |
Posted by: bilbomacuser on 2023-04-04 02:29:20
I recently bought an LC 475. At first it did that weird repeated pipping sound that I associate with power supply issues - so I recapped the power supply and motherboard, and apart from some issues with the hard drive eventually got it working. I had it booting consistently from an internal BlueSCSI V2 whilst also having a BlueSCSI V1 connected externally. I put a new 32 MB SIMM as well as upgraded the VRAM to 1MB. All was good - except it took a long time before any video output would appear - I assumed this was the time it was taking to test the large amount of memory.
However, a week later and I power it on without changing anything - I get a chime, but video never appears. However, pressing Apple-Control-Reset does cause it to re-boot (startup chime sounds). It has a new battery. I've tested by removing the RAM and the extra VRAM and this didn't make any difference (it has onboard RAM and VRAM).
Any ideas how to investigate this further? |
Posted by: joshc on 2023-04-04 02:36:19
Got any pics of your board?
What voltages are you getting from the power supply?
Tried a different DB15 adapter? |
Posted by: Phipli on 2023-04-04 02:39:39
except it took a long time before any video output would appear - I assumed this was the time it was taking to test the large amount of memory. Your assumption is correct. With that much RAM expect ~30 seconds of blank screen.
I know you said it has a new battery, but this is what a bad battery does exactly. Try powering on, switching the power off for half a second then back on. Does it start then? |
Posted by: bilbomacuser on 2023-04-04 02:52:50
The voltages are correct, eg. 12.1V, 4.99V, -5.01V. I don't have another DB15 adapter but I could try a proper Mac monitor later. The board looks in good condition. |
Posted by: bilbomacuser on 2023-04-04 02:55:24
The battery measures 3.6 volts
Oddly when I tried the power on, power off half a second, then power on - the monitor now says Input Not Supported - whereas it had been displaying correctly at the different resolutions I tried last week. |
Posted by: joshc on 2023-04-04 03:00:49
I've tested by removing the RAM and the extra VRAM and this didn't make any difference (it has onboard RAM and VRAM). I don't think the 475 has any onboard VRAM.
Have you got any spare VRAM SIMMs to test with? |
Posted by: Phipli on 2023-04-04 03:08:54
Input Not Supported Double check your adapter dip switches. What are they set to?
Like joshc says, you must have VRAM installed. |
Posted by: bilbomacuser on 2023-04-04 06:28:40
Had tried it with and without the new VRAM - can I try swapping back the original VRAM just in case it's that. I don't think there are any dip switches. The monitor settings haven't changed since last week when it was working ok. |
Posted by: MrFahrenheit on 2023-04-04 06:34:08
What VRAM are you using? If possible can you provide photos of that (front and back)? As joshc said, the 475 doesn’t have any on-board VRAM and both sockets are required to be populated.
Did you overclock this machine to 33mhz?
Have you tried turning on with command option p r held down, and wait for at least 3 chime boot loops before releasing? Also worth a shot but try with 10 boot chimes before releasing.
Also, with the machine off, press and hold the red button on the logic board for 10 seconds then release. Wait 30 seconds and try powering on. |
Posted by: bilbomacuser on 2023-04-04 06:38:00
I bought VRAM from an eBay seller in France, 2 x 512MB, purple coloured boards. Haven't overclocked it. Command option P R doesn't seem to work. |
Posted by: bilbomacuser on 2023-04-04 06:40:35
No different with the original 2 x 256MB VRAM it can with. Just tried. |
Posted by: bilbomacuser on 2023-04-04 06:42:57
Just tried the Red button suggestion but not didn't make any difference. |
Posted by: bilbomacuser on 2023-04-04 06:46:10
Hmm, after trying various combos, the original VRAM and with the RAM module removed has just started up. Not sure if a coincidence, as there have been some inconsistencies since I got this computer.
Update - not repeatable. Changed nothing yet back to the same issue. |
Posted by: Phipli on 2023-04-04 06:58:41
Hmm, after trying various combos, the original VRAM and with the RAM module removed has just started up. Not sure if a coincidence, as there have been some inconsistencies since I got this computer.
Update - not repeatable. Changed nothing yet back to the same issue. Try putting the VRAM in and out a few times (with the machine off) to clean the contacts. If you have contact cleaner, spray it in the VRAM slots.
Do all your testing without a RAM SIMM because it is fewer things to consider. Until the screen starts working.
Unplug the hard disk too, so you don't corrupt your System by cutting the power while it is booting hidden in the background, or whatever. It isn't needed for this testing. |
Posted by: bilbomacuser on 2023-04-04 07:06:07
Good idea. Although it's not consistent, the most consistent way of getting the display working is by holding the red button down for 10 seconds, then waiting 30 seconds and powering on. With the RAM SIMM removed and the hard drives disconnected I get he floppy symbol - but if I power off, wait 10 seconds and then power on the display again doesn't come on.
Update: the most consistent way of getting it to work is: No RAM SIMM module; power off; wait 30 seconds; power on. I then tried adding the BlueSCSI internally, and it still works, and boots (but warns not enough memory). Adding the SIMM module (either the original 4MB module or the 32 MB module. So perhaps I'll try contact cleaner on the RAM socket. Any best way of doing that - is it harmful to get it on anything else? |
Posted by: Phipli on 2023-04-04 07:08:08
Good idea. Although it's not consistent, the most consistent way of getting the display working is by holding the red button down for 10 seconds, then waiting 30 seconds and powering on. With the RAM SIMM removed and the hard drives disconnected I get he floppy symbol - but if I power off, wait 10 seconds and then power on the display again doesn't come on. Did you was the board during the recap? How well did the recap go? Any trouble? |
Posted by: Phipli on 2023-04-04 07:09:15
Also, where are you (approximately)? In case you're two miles down the road from one of us. |
Posted by: bilbomacuser on 2023-04-04 07:20:48
I cleaned off the flux thoroughly with isopropyl alcohol, but didn't submerge the board. Recap went very well - for the surface mount capacitors used 2 soldering irons to simultaneously melt each site and lift the caps off, then solder wick to clean the pads, flux, then new solder on the pads. Flux on the soldered pads, tten capacitors on the solder, then heated each side separately with iron until reflowed.
I'm in the UK, not too far from Bristol. |
Posted by: Phipli on 2023-04-04 07:50:38
I'm in the UK, not too far from Bristol. Heartland of UK based MLAers 🙂
I'm in the Midlands though, doesn't seem to be anyone else willing to admit they live near here though. |
Posted by: bilbomacuser on 2023-04-04 14:33:03
Had thought the chance of you being in the UK was negligible! |
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