Macintosh SE/30 Black Screen

[Tribble]

Hello and thanks for having me.

I aquired an SE/30. When I started it I had a picture which was off-centre. I have since found out I could have just removed the casing and adjusted the pots. As you can tell, I'm new to old CRT computers.

However, I did read that it can be caused by bad caps. I replaced all the caps but ripped one pad off. I jumped it with a wire which I thought would fix the broken trace. When I boot the machine I now have a black screen. There is no boot sound but I don't recall there being one before.

I did make a mess of taking some capacitors off.

Here are 2 pictures of the mess I've made.

C4 - I think can join to the via on the right.
C5 - I don't know where I would rejoin this from.
C6 - Should go to the trace above the C4 via
C12 Should attach to the via to the left

That is what I think anyway.

[Mark1960]

C5 might have had a via within the missing pad. Is this pcb multilayer or only double sided?

Can you identify the missing via on the opposite side of the pcb? It might be easier to mount the capacitor on the opposite side, or thread a wire through the hole of the missing via.

[TonyDuell]

Which board are you working on? The pictures look like the 'digital board' which is flat at the bottom of the machine.

If the schematics I have are correct and applicable, then :

C4 +ve to UB11 pin 10, -ve to R12 (180R)
C5 +ve to UB10,UB11 pin 15, -ve ground
C6 UB11 pin 7 and ground (this capacitor is unpolarised)
C12 +ve to the +5V rail, -ve ground.

C4-C6 are all associated with the sound circuit, in particular the right hand channel, but none of these capacitors should prevent the machine from producing video

[Tribble]

Thanks Mark, I'll have check tonight.

I'm open to sending to anyone to have a look for me to see where I have gone wrong.

[Tribble]

Thanks Tony, that is very interesting.

I'll post later the board type.

[SiriusHardware]

As has been said, the most likely thing that's happened is that you have accidentally pulled one of the conductive circular through-hole 'tubes' out of one of the holes along with a capacitor lead. (That is, if the PCB is double sided). This is especially likely where the capacitor leads were bent over before being soldered, or where they have cranked 'clip in' leads, as some of the bigger capacitors do.

If you ever try to remove capacitors again, first make sure the capacitor leads are completely straight - I melt the solder with a soldering iron in one hand and use a Stanley knife blade to lift and bend the capacitor pin straight upright while the solder is melted. Don't try to lift / bend the capacitor leads with the iron tip, as it risks damage to both the iron tip and the solder pad. Irons are for melting solder with, nothing else.

Don't Panic: You can fix this. This is a clear case of cause and effect. It was working normally (ish) before you recapped it, and then while recapping, you inadvertently did something which broke it.

The first thing to do is to go patiently back over everything you did, one capacitor at a time - removing each capacitor again if necessary - to check the condition of the pads and through-hole connectiions (if it is a double sided PCB).

If you've still got the original capacitors have a look at all of their pins to see if any them are wearing a tell-tale copper coloured 'anklet'.

[TonyDuell]

I am fairly sure the original capacitors were surface-mount devices.

[Tribble]

The board is 820-0260-A.

It's double sided.

All the caps were SMCs and one was an axial through the board.

Originally Posted by TonyDuell

Which board are you working on? The pictures look like the 'digital board' which is flat at the bottom of the machine.

If the schematics I have are correct and applicable, then :

C4 +ve to UB11 pin 10, -ve to R12 (180R)
C5 +ve to UB10,UB11 pin 15, -ve ground
C6 UB11 pin 7 and ground (this capacitor is unpolarised)
C12 +ve to the +5V rail, -ve ground.

C4-C6 are all associated with the sound circuit, in particular the right hand channel, but none of these capacitors should prevent the machine from producing video

Hi Tony,

Could you tell me the connections for;

C8, 9 and 10 please?

Thanks,

Pete.

[Keith956]

Originally Posted by TonyDuell

I am fairly sure the original capacitors were surface-mount devices.

That's what I thought too. Just need some fine wire to connect back to the broken tracks - fiddly but doable.

[Tribble]

Originally Posted by Keith956

That's what I thought too. Just need some fine wire to connect back to the broken tracks - fiddly but doable.

I have some fiddly enamelled wire Keith

[TonyDuell]

Originally Posted by Tribble

Could you tell me the connections for;

C8, 9 and 10 please?

Thanks,

Pete.

C8 : -ve to the -5V rail (e.g. pin 6 of the video connector), +ve ground
C9 : -ve to the -12V rail (e.g. pin 7 of the video connector), +ve ground
C10 : +ve to the +12V rail (e.g. pin 14 of the video connector), -ve ground

[Tribble]

Thanks Tony.

[SiriusHardware]

I am fairly sure the original capacitors were surface-mount devices.

Are we at the point where even retro devices contain SM capacitors?

(Sorry, I didn't see the pictures earlier).

[Tribble]

I’ve checked the remaining pads and they are all connected where they should be. I have since found a schematic of the board. That makes the job infinitely easier. I’m just waiting for the axial capacitor to turn up and I can repopulate the board.

Obviously I’ll post what happens after.

I’d like to take the opportunity to that you for all the help so far. It’s great to get such good feedback so quickly.

[Tribble]

On the side where the video ROM is, there is a row of pads (on J14?) that don't appear to do anything.

Can you enlighten me as to what they do?

[TonyDuell]

Can you post a photo of the appropriate part of the PCB?

I don't know offhand what those pads are for. Maybe factory testing?

[Tribble]

Hi Tony.

Here is a picture. I found a schematic and worked out which pin is which. I don't know what they do though. Probably test pins as you said.

Cap C4. Does it matter which side the -ve goes on the resistor R12?

[Tribble]

I populated the board all except the C4, which is for the sound.

I still get no picture.

Here is a picture of the neck of the vacuum tube. It looks brighter in the picture. I am still thinking that something happened on the analogue board. Do you agree?

[cmjones01]

You'll get nothing at all on the screen of a Mac SE/30 if the logic board isn't working at least a bit. One of the outputs from the logic board is the drive which goes directly to the line output stage, and without it there will be no scanning, no EHT and no raster of any kind. A running but faulty logic board will produce a 'rug pattern' of random-ish black and white dots on the screen.

Faults in the video circuitry are quite common, I understand. My own SE/30 had several which required some of the 74 series discrete logic to be replaced. Even without the video output working, the board should still make the 'bong' startup sound or the 'chimes of death' if it's not happy. That requires the electrolytic capacitors to be in good shape, though. The sound is one of the first things to disappear when the surface-mounted electrolytics dry up.

Chris

[TonyDuell]

What test equipment do you have, if any? Multimeter, oscilloscope, logic probe, logic analyser?

At this point I'd check the power rails to the digital board with a multimeter to be sure the power supply is working correctly (it must be doing something for the CRT filament to light, which I think runs off the 12V supply).

Then use a 'scope, logic probe or logic analyser to look for activity on the vertical and horizontal drive outputs and the video outputs of the logic board. This will indicate if the thing is producing video or not.