Quadra 610 - Plays boot chime but no video

[activepilot]

Hi all, happy New Year! I'm trying to repair a Quadra 610 that I got some time ago together with a DOS compatibility card. The PSU outputs look fine, but there were some leaked capacitors.

So far I have changed all the electrolytic capacitors (10x 47µF 16V), cleaned the leakaged with isopropyl alcohol and replaced the battery. Now I get a boot chime (yay!) but sadly no video output. I tried both with a Color Display and a VGA LCD display using an adaptor, but still no luck. The CPU does get warm, and a few other ICs around do as well, so I assume the board does turn on correctly.

Here's some pics of the board:

• View attachment DSC06463.JPG
• View attachment DSC06464.JPG

I checked the DB-15 video connector pins with an oscilloscope, and I do see a signal on the red, green and blue pins. However, CSYNC and VSYNC are both stuck at 5V and HSYNC is always at 0V, which seems odd. I found a nice reference on how the video output works here: https://www.bigmessowires.com/2023/...d-designing-a-mac-to-vga-adapter-with-lm1881/.

Does anyone have a clue what might be going on and what I can try next? Some tips on how to debug the video issue are also appreciated.

 

[Daniël]

What happens after a fast power cycle after initially powering up the Mac?
You basically want to power it up, then power it off and on again, fast enough that the capacitors don't fully drain, but not so fast that it doesn't properly trigger a new startup sequence.

If that works, something related to the battery circuit might be affected in a way that stops the battery's power from getting to the rest of the system, meaning the video circuitry won't properly initialize on a cold boot. Have you checked if the battery's charge is OK as well?

 

[Phipli]

What happens after a fast power cycle after initially powering up the Mac?
You basically want to power it up, then power it off and on again, fast enough that the capacitors don't fully drain, but not so fast that it doesn't properly trigger a new startup sequence.

If that works, something related to the battery circuit might be affected in a way that stops the battery's power from getting to the rest of the system, meaning the video circuitry won't properly initialize on a cold boot. Have you checked if the battery's charge is OK as well?

I think the 610 starts without a battery.

 

[activepilot]

What happens after a fast power cycle after initially powering up the Mac?
You basically want to power it up, then power it off and on again, fast enough that the capacitors don't fully drain, but not so fast that it doesn't properly trigger a new startup sequence.

If that works, something related to the battery circuit might be affected in a way that stops the battery's power from getting to the rest of the system, meaning the video circuitry won't properly initialize on a cold boot. Have you checked if the battery's charge is OK as well?

Doing a fast power cycle just plays the boot chime again, but still no video output.

The battery is brand new, and it does output 3.6V - I also tried without a battery, but same results.

I read that the Quadra 610 has on-board RAM and VRAM, so for now I'm testing it without any extra memory modules.

 

[Phipli]

Check the pins if the chip U21 at the corner next to C45. I've seen two C610s with pins that the cap goo has freed on that corner, although with different symptoms to yours.

Nudge they pins very gently with a scalpel to see if they are detached from their pads. If they are, extreme care is needed repairing, because the pads are slightly proud of the surrounding area, and have a habit of getting stuck off to one side. Just ask @max1zzz @mg.man

 

[Daniël]

I think the 610 starts without a battery.

I owned one (since sold to a friend of mine), and I remember it needing the battery. I know there's some debate whether this model needs it, I wouldn't be surprised if this differs from board revision to board revision, or maybe even video IC revision.

 

[Phipli]

I owned one (since sold to a friend of mine), and I remember it needing the battery. I know there's some debate whether this model needs it, I wouldn't be surprised if this differs from board revision to board revision, or maybe even video IC revision.

Fair enough. Mine reliably boots without a battery.

 

[activepilot]

Check the pins if the chip U21 at the corner next to C45. I've seen two C610s with pins that the cap goo has freed on that corner, although with different symptoms to yours.

Nudge they pins very gently with a scalpel to see if they are detached from their pads. If they are, extreme care is needed repairing, because the pads are slightly proud of the surrounding area, and have a habit of getting stuck off to one side. Just ask @max1zzz @mg.man

They seem fine, at least all the pins of the IC are still attached to the pads.

 

[Phipli]

They seem fine, at least all the pins of the IC are still attached to the pads.

You've poked (very gently) them? Not just looked? You can't tell by looking.

 

[activepilot]

You've poked (very gently) them? Not just looked? You can't tell by looking.

Yes, I carefully poked them and they are still firmly attached. Also tried some of the other ICs near cap leakage, but none seems to be detached.

 

[Phipli]

Yes, I carefully poked them and they are still firmly attached. Also tried some of the other ICs near cap leakage, but none seems to be detached.

Good news

Given it happy chimes, it is almost certain the CPU, RAM, reset, sound and ROM are good.

I'd start by thinking what is after that and needed for video. Obvious thing that springs to mind is the clock that feeds the video sub system : G1 (near U21 that you just looked at). Does pin 3 have a clock signal?

 

[Phipli]

Also, check where that signal goes and see if the clock is present at the other end(s) of the trace(s). Or check continuity with the power off.

 

[activepilot]

Good news

Given it happy chimes, it is almost certain the CPU, RAM, reset, sound and ROM are good.

I'd start by thinking what is after that and needed for video. Obvious thing that springs to mind is the clock that feeds the video sub system : G1 (near U21 that you just looked at). Does pin 3 have a clock signal?

I do see a signal on pin 3 of G1 (it seems to be oscillating around ~2-4V, I can't see the signal clearly with my oscilloscope), but can't see where it goes; from pin 3 it goes under the board to R131, and from there it seems to go to one of the pins of U21.

Same story with G3 as well, I think that trace goes either to U26 or to the SONIC IC.

 

[Phipli]

I do see a signal on pin 3 of G1 (it seems to be oscillating around ~2-4V, I can't see the signal clearly with my oscilloscope), but can't see where it goes; from pin 3 it goes under the board to R131, and from there it seems to go to one of the pins of U21.

Same story with G3 as well, I think that trace goes either to U26 or to the SONIC IC.

What frequency is your scope?

 

[activepilot]

What frequency is your scope?

Just 20 MHz.

 

[Phipli]

Just 20 MHz.

Yeah, it isn't fast enough - what you're seeing is probably a good clock as undersampling would give a reading between 0 and 5v from a ~31MHz clock.

 

[Phipli]

BTW, I use one of these for measuring frequencies. It doesn't let you know the quality of the square wave or whatever, but it does pretty accurately tell you if the correct frequency is coming out. They're cheap as long as you don't mind doing a bit of soldering.

Digital LED Tester Kit Crystal Oscillator Meter Frequency Counter DIY Kits | eBay

1 x 1Hz-50MHz Frequency Counter Kit. Frequency range: 1 Hz-50 MHz. Crystal Test Range: 4 MHz-48 MHz. Five digits accuracy. Due to the difference between different monitors, the picture may not reflect the actual color of the item.

www.ebay.co.uk

You can get them even cheaper direct from China. It is a good tool to have on the side for vintage computer repair. Busses didn't exceed the 50MHz limit of these boards until the G3 era.

 

[Phipli]

What country are you in? If you don't mind my asking - I'm UK based.

 

[activepilot]

BTW, I use one of these for measuring frequencies. It doesn't let you know the quality of the square wave or whatever, but it does pretty accurately tell you if the correct frequency is coming out. They're cheap as long as you don't mind doing a bit of soldering.

Digital LED Tester Kit Crystal Oscillator Meter Frequency Counter DIY Kits | eBay

1 x 1Hz-50MHz Frequency Counter Kit. Frequency range: 1 Hz-50 MHz. Crystal Test Range: 4 MHz-48 MHz. Five digits accuracy. Due to the difference between different monitors, the picture may not reflect the actual color of the item.

www.ebay.co.uk

You can get them even cheaper direct from China. It is a good tool to have on the side for vintage computer repair. Busses didn't exceed the 50MHz limit of these boards until the G3 era.

Nice! I may go ahead and order one, never had to test for bad oscillators.

What country are you in? If you don't mind my asking - I'm UK based.

I'm in Spain

 

[Phipli]

I'm in Spain

Good to know - if you stick your country in your profile it means we can quickly check if we're gauging how easy it is to post you something (for example, I have spare ~31MHz clocks if you had needed one (which I don't think you do)).