Apple macintosh Quadra 605 not posting - no chime/video

[slaanesh]

I recently bought a Macintosh Quadra 605 And completed the following work.
I checked the power supply and recapped it completely and it works like a champ rock steady voltages at the expected levels,
I recapped the board using tantalum caps. Everything seemed to go really well. No pads damaged and only a bit of cap goo mainly around the top-left part of the board. cleaned it thoroughly with loads of 99.9% IPA.

Anyway it doesn’t boot or even post. No chime or video. I’ve tried a known good CRT and adapter with LCD.

I’ve checked the speaker and it’s showing a good 16.2 ohms resistance which is spot on. I’ve checked the speaker out connector and the switch is working and should be routing to the internal speaker.

im starting it with fan, HD but no SIMMS at all just the onboard RAM. I’ve tried with and without the PRAM battery but no difference. I’ve pressed the CUDA button several times.
I’ve checked the power to the various caps and it all looks good. With my scope w I’ve checked the oscillator and it’s getting a good steady oscillation.

What I don’t see is any activity on the RAM. I’m wondering if the CPU is even getting out of reset state?
how to check? The MC88920 controls this state and I believe RST_IN and RST_OUT control this but the later is always low.

Attached is a photo of the board just before recapping.

Any suggestions?

 

[killvore]

This may be super obvious but you didn't mention it - do you have a battery installed? iirc these won't post without a battery

 

[slaanesh]

Do you mean it won’t post and no chime without a battery? All my last testing has been without battery.

 

[beachycove]

The machine needs a battery, or you can flip the power switch off and on quickly after the grey screen first comes up.

 

[zigzagjoe]

Iirc mine will chine but no video without the battery. Do you get any speaker pop when powered on?

 

[joshc]

Iirc mine will chine but no video without the battery. Do you get any speaker pop when powered on?

This is what I remember as well, it should still chime without a battery.

 

[slaanesh]

Iirc mine will chine but no video without the battery. Do you get any speaker pop when powered on?

No it doesn't pop when powered on.

I touched all the ICs with my finger tip. Only the 68040 is really producing any sort of warmth.

I sampled a few random lines with my scope on RAM chips. Usual activity is absent, they are flat or +5V with one having a waveform. Bur I only sample a few, expecting to find data/address line with activity, but none.

 

[slaanesh]

I read that C127 and C128 were a weak spot but I've checked my photo and I've tested continuity to C127, C128 and C129 (several times) and they were all good on both sides (5V, 12V and -5V and GND). These are the power filter caps closest to the power input cable.

 

[killvore]

I had to redo C36 on my LC475, the traces go really close to the pad and my capacitors are too big. Might be worth taking another look especially if you have bad mask? (C35 might have similar) These are the ones next to the RAM socket, though I don't know if they are actually involved with the RAM at all. Sorry for potato quality photo!

 

[slaanesh]

I had to redo C36 on my LC475, the traces go really close to the pad and my capacitors are too big. Might be worth taking another look especially if you have bad mask? (C35 might have similar) These are the ones next to the RAM socket, though I don't know if they are actually involved with the RAM at all. Sorry for potato quality photo!

yes thank you excellent suggestion I have found a culprit C127 solder squidged out and grounded A0! Bad!
I will redo it tomorrow morning when I am fresh and check for others!

 

[slaanesh]

So I fixed C127 and also ended up checking most of the other caps and replaced C136, C137, C149 and C150 with smaller ceramic caps… not sure if these will be ok but I just wanted to make sure that nothing else was shorting in that area.
so after this I got some video but it’s still not healthy and still no sound.

 

[slaanesh]

Ha I hadn’t put the VRAM SIMMs in … it works!
yay but no sound…

 

[joshc]

so the opamp on these can have problems, and/or the components connected to it. all in the top left corner of the board

The sound chip (DFAC) is also near capacitors that leak into it, so worth checking that area over. Sometimes removal of the chip is necessary to clean under it properly

Do you get sound from headphones?

 

[slaanesh]

Do you get sound from headphones?

yes, I do - a nice, strong, clear chime so presumably either trace going to the speaker - which I doubt as the board looks really clean and good or more likely the opamp.
i don’t have a spare for this so I will order one in.

 

[slaanesh]

Okay so the new DA7052 op-amps arrived. I took the old one out, put in a new one and BINGO, we got sound from the internal speaker.
It couldn't be anything else.
The old one still looked completely fine.

So that's everything AFAIK working. Now I can finish "building" the system and install an OS, etc.

And play some games!