Macintosh SE/30 Black Screen

[Keith956]

Originally Posted by Tribble

Thanks Keith,

Where do the probes go? One has a yellow ring on the base of the connector to the scope and the other has a mauve ring. Or doesn't it matter? Does one need to be on ground?

Sorry but I am learning all this and really appreciate the help.

Have you measured the supply voltages yet? As there's not much point using the scope until you've verified that all the power rails are correct.

The scope probes - looks like its a dual channel scope so there are two of them - should have a ground crocodile clip and a probe tip. The clip goes to GND, you probe the signal with the probe tip. From the photo, looks like yellow is the channel1 signal and purple the channel2.

[Tribble]

As far as I can tell all the power rails are there.

[Tribble]

I am currently watching a youtube video of learning the basics of oscilloscopes.

Hopefully I'll know more tomorrow.

Pete.

[ortek_service]

Originally Posted by SiriusHardware

If I can repeat an earlier suggestion, can you guide tribble to where there will almost certainly be a signal for his scope to look at so he can get the hang of using the scope?

I think others have now stated that the two oscilloscope channels are effectively independent and whilst some 'scopes with do subtraction between the two you really need a (ground) reference on at least ones of these (possibly both, if the 'scope has isolated-ground inputs)

So ensure the associated ground wire clip is connected to a good circuit ground - sometime a a heatsink can be grounded, but not always - if in doubt use a DMM on resistance / continuity to check there is approx 0R resistance to the a known ground (0V) in on a power connector.

Originally Posted by SiriusHardware

At the moment we don't know if there are drive/sync signals for his scope to see once it is properly set up, so it may be better to look at circuit points which are almost sure to have active signals on them first.

I think the problem with being able to say where to look for a signal is at present we don't know how much (if any) of the circuitry is actually running (Although if +5V is on the Digital board, then hopefully the main clock for the CPU etc should be present).
That's why I suggested using the 'scope-meter's built-in function generator, to get some familiarity with it, first, to ensure a signal is actually present.

[ortek_service]

Originally Posted by Tribble

As far as I can tell all the power rails are there.

Can you tell us what board, connector number and what DC voltages you measured on each pin ?
- We can then check that thee are actually correct, rather than just a voltage being present. And can hopefully spot any that look abnormal.

I would suggest measuring the voltage at the connector directly on the outputs of the PSU module itself, to start with, to confirm whether that looks OK - as it had been suggested in a fault guide that this was most likely to be at fault.

[Tribble]

Thanks Ortek.

I'll do all that tomorrow. I'll measure the logic board and analogue board outputs as best I can.

[ortek_service]

I thought it would also be a good idea to try and measure the PSU Module outputs, directly, to check that first.

And I presumed there would be info on the 'net showing which board this plugged into / a block diagram / service manual for this. But surprisingly I struggled to find much on these!

I have eventually worked it out from the Schematics for the SE/30 at:
https://www.macintoshrepository.org/875-macintosh-se-30-schematics-and-repair
- I've attached a copy with MacOS bits removed to make ZIP under 4MB
(Plus also relevant sheets, directly for ease of access but may get compressed)

But even these aren't too easy to follow (especially the poor-quality scans of the original Apple originals. so the Bomark Services RevEng / Redraws are much-more readable - Although I've found these have an error with two Pin9's / No Pin 7 on P3 PSU connector on Monitor's 'Analog' (CRT) board!).

So for info to everyone, I've found the Mains-PSU Module plugs into Monitor High-Voltage 'Analog' board into P3.


P3 (PSU Plug) pin functions / wire colours :
Pins 1,2,3,7,8 (Black) = 0V (Gnd)
Pins 4,9 (Orange) = +5V @6A
Pin 5 (Yellow) = +12V(digital) @2.1A
Pin 6 (Green) = -12V
Pin 10 (Red) = +12V(monitor) @1.25A

Note: Confusingly, there are actually two (isolated from each other) separate +12V outputs, with different current ratings!
With only one being passed to the digital circuitry, and the other just to power the monitor (Heaters, Field output stage IC, and the line-output HT/EHT step-up transformer stages).

On the Monitor board, most of these supplies are then passed to the 14way P4 connector, which connects (1:1 wired) to J12 on the Digital board.
There is also an additional -5V regulator (fed from the -12V supply) on the Monitor's 'Analog' board, whose output then also feeds into the Digital Logic board.

P4 (= J12) pin functions / wire colours :
Pins 1,2,3,4,5,8 (Black) = 0V (Gnd)
Pin 6 (Blue) = -5V (From 7905 1A reg)
Pin 7 (Green) = -12V
Pin 9 (White = Composite video ('Data') (Drive to CRT Cathode-driver transistor)
Pin 10 (Violet) = Horiz Sync (Drive to Line Output stage transistors)
Pin 11 (Grey) = Vert Sync (Drive to Field Deflection output IC)
Pins 12,13 (Orange) = +5V @6A
Pin 14 (Yellow) = +12V(digital) @2.1A


Note: As these are 2-row connectors there can be different ways of pin-numbering, even when you know where pin 1 starts! Some number one row as odd and the other as even. Whereas some number sequentially down one row the go back up the other side (like IC's), or continual numbering on the second-row, opposite pin 1.
Good board assembly etc drawings would have been useful, to identify this, but wire colours should also allow this to be identified fairly-easily as they have nicely colour-coded each function.

[ortek_service]

BTW: I did also find this webpage about changing the SMT capacitors inc. tips on removing them without stressing the pads too much: https://sharebrained.com/vintage/computer/apple/mac-se30/

And also this page on running / testing the Logic Board without the Monitor's 'Analog' board, using an RGB2HDMI converter and a PC PSU: https://68kmla.org/bb/index.php?threads/running-a-macse-30-without-an-analog-board.38857/

Note: The Logic Board J12 pinout linked from here at: https://old.pinouts.ru/Power/macclassicpower_pinout.shtml
is for the 'Classic' and whilst similar it is reverse numbered as well as some pins having slightly-different functions!

[Tribble]

Originally Posted by ortek_service

P3 (PSU Plug) pin functions / wire colours :
Pins 1,2,3,7,8 (Black) = 0V (Gnd)
Pins 4,9 (Orange) = +5V @6A =+5V
Pin 5 (Yellow) = +12V(digital) @2.1A =+18v
Pin 6 (Green) = -12V =-12v
Pin 10 (Red) = +12V(monitor) @1.25A =+18v

Note: Confusingly, there are actually two (isolated from each other) separate +12V outputs, with different current ratings!
With only one being passed to the digital circuitry, and the other just to power the monitor (Heaters, Field output stage IC, and the line-output HT/EHT step-up transformer stages).

On the Monitor board, most of these supplies are then passed to the 14way P4 connector, which connects (1:1 wired) to J12 on the Digital board.
There is also an additional -5V regulator (fed from the -12V supply) on the Monitor's 'Analog' board, whose output then also feeds into the Digital Logic board.

P4 (= J12) pin functions / wire colours :
Pins 1,2,3,4,5,8 (Black) = 0V (Gnd)
Pin 6 (Blue) = -5V (From 7905 1A reg) =-5v
Pin 7 (Green) = -12V =-12v
Pin 9 (White = Composite video ('Data') (Drive to CRT Cathode-driver transistor)
Pin 10 (Violet) = Horiz Sync (Drive to Line Output stage transistors)
Pin 11 (Grey) = Vert Sync (Drive to Field Deflection output IC)
Pins 12,13 (Orange) = +5V @6A =+5v
Pin 14 (Yellow) = +12V(digital) @2.1A =+18




Note: As these are 2-row connectors there can be different ways of pin-numbering, even when you know where pin 1 starts! Some number one row as odd and the other as even. Whereas some number sequentially down one row the go back up the other side (like IC's), or continual numbering on the second-row, opposite pin 1.
Good board assembly etc drawings would have been useful, to identify this, but wire colours should also allow this to be identified fairly-easily as they have nicely colour-coded each function.

It seems odd that I'm getting 18v where I should have 12v.

[Tribble]

I have been measuring voltages on the CRT board. All the resistors seem to have voltage except R4. It measures correctly at 100K ohms. I don't know if it should have voltage.

[Keith956]

That resistor would appear to be the 100k connecting to the grid of the CRT. According to the schematic, it's supposed to have -34 to -62v depending on the brightness control.

Before probing around that section too much (which has some nasty volltages in it, so beware!) I'd want to check if the hsync and vsync were active - P4 pin 11 has vsync at 60Hz and pin 10 has hsync at 22.25KHz. If the latter is not working there will be no HT for the CRT.

Also the +18v reading is odd. I wonder if you can re-check the +12v supplies.

[Tribble]

Hi Keith.

I rechecked the 12v and they are 12v. No idea where 18v came from!

I can't seem to get any reading from the v and hsync.

Where to now?

[TonyDuell]

The main problem is that we don't know if the lack of signal on hsync and vsync is a fault in the Mac or your inexperence with the 'scope.

Does anyone know if this 'scope will handle a repetetive 32MHz signal? If it is known that it will, I'd suggest looking at the master clock on pin 8 of UH7 on the logic board. This is very likely to be present (OK, the oscillator Y2 could have failed) so if you can't detect it it suggests mishandling of the 'scope.

[Keith956]

Originally Posted by TonyDuell

Does anyone know if this 'scope will handle a repetetive 32MHz signal?

A quick Google image search show Elektor sell it as the DSO3D12, and it's a 120MHz 250Msample/s job. So it should do.

[Tribble]

I'll check that Tony.

[Keith956]

Originally Posted by Tribble

I can't seem to get any reading from the v and hsync.

When you say reading, is that with a scope probe on the pin(s) (and with the probe ground clip on ground?

You will also need to set the X axis sweep of the scope (for vsync around 20mS/div, for hsync around 50uS/div). And a Y axis sensitivity of say 1V/div.

[Tribble]

I've found UH7 but I can't find which pin is 8.

I'll check the syncs again using those settings after I read pin 8.

[Tribble]

Probing all the pins on UH7 I actually got a reading. It was 31.5Hz which is close enough for me. Still no reading on P4.

[Keith956]

Originally Posted by Tribble

Probing all the pins on UH7 I actually got a reading. It was 31.5Hz which is close enough for me. Still no reading on P4.

Do you means 31.5MHz?

And P4, that's probing vsync/hsync signals with the scope?

[Tribble]

D'oh! Yes, 31.5MHz.