Macintosh SE/30 Black Screen

[Tribble]

Thanks Chris.

There is no bong yet as I'm waiting for a couple of new caps to arrive.

Once they are on if I still don't get any noise I'm not sure where to go.

[TonyDuell]

Originally Posted by Tribble

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

Sorry, missed this.

One side of R12 is connected to R4 and to pin 2 of the filter L2. C4 connects to the other side of R12.

[Tribble]

Hi Tony.

I only have a multimeter sadly. All I can really do is check for voltages.

[Tribble]

Originally Posted by TonyDuell

Sorry, missed this.

One side of R12 is connected to R4 and to pin 2 of the filter L2. C4 connects to the other side of R12.

Thanks Tony.

[SiriusHardware]

Tribble, does your multimeter have a frequency or 'Hz' measurement range or feature? If it does that could help to check some signals, like the line output drive signal Tony mentioned.

[Tribble]

Hi Sirius, I only have OHM, DCV, ACV, DCA, DCV and hfe.

I've managed to knock off one side of R34. I need to know where they go to in case the pad has come off.

Thanks,

Pete.

[TonyDuell]

One side of R34 goes to ground, the other to pin 3 of UA9

[Tribble]

Thanks Tony.

As far as RAM goes, I didn't notice their position when I took them out first time.

I have 8 modules.

4 are NEC 421000-70
4 are Siemens HYB511000AJ-70.

Do they need to be in any particular order in the simm slots?

[Tribble]

Lucky for me R34 connections are still intact.

[Tribble]

I watched a video on YouTube by Adrian's Digital Basement where he tested if a CRT had high voltage output using a mini fluorescent tube. It lit up when next to the neck to the CRT.

I have ordered such tube after looking over the logic board and not seeing anything untoward. I can't tell if it is the logic board playing up or not. I suppose it is possible I have dislodged a solder joint somewhere.

Pete.

[Temporalnexus]

If you haven't changed the battery on the board it also won't boot, Apple's of that period wouldn't do anything if the internal battery was flat

[Tribble]

Hi Courtney,

I did change the battery.

[Tribble]

I bought the mini flourescent tube. The tube didn't light up like Adrian's did.

I am leaning towards the analogue board now.

Can you suggest what to look for? I am getting a glow on the neck as mentioned before.

There is still no bong but the speaker only measured 3 ohms. So that could be faulty.

[ortek_service]

The glow at the CRT neck will just show that it is getting an OK supply to its heaters.

You can sometimes tell if a CRT is getting an OK EHT supply, by feeling for the static charge build-up on the FRONT (viewing) face of the CRT, by putting the back of your hand against that at switch-on. Or listening for a 'rustle / crackle' sound at switch on.

You could also try measuring some other, lower-voltage, supplies that are also derived from the Line OutPut Transformer (LOPT) - after their rectifier diode, so can be measured at DC - to check this is being driven.
Normally the CRT Heaters also come from this, but it seems this monitor may be a bit-different.


Re: Speaker
3R at DC is probably typical for many small speakers
- The stated 'Impedance' on these (e.g. 8R, 4R, 32R etc) also includes their (Inductive) reactance at (usually) 1kHz.
(So they will measure quite a bit lower on a standard DC Multimeter)
And speakers do not tend to go partially short-circuit (especially low-power ones, that can't get enough power to damage them).

You could also test it, by connecting it up to a headphone jack of an audio player (or a Hi-Fi amp Loudspeaker output - but keep volume v.low to avoid damaging these low-power speakers).

You could also connect some headphone to the computer's speaker output, after disconnecting that.
However, I suspect the problem is elsewhere and that it isn't running to produce the 'bong' sound to drive the speaker.

[TonyDuell]

According to the schematic I have for one version of the analogue board, the CRT runs off a 12V output from the main power supply. So a glow from there does not imply the horizontal output stage is running.

There is no horizontal oscillator. The horizontal system depends on the drive signal from the digital board, if that's missing you'll get no high voltages. So lack of them could mean a problem on the analogue board or the digital board.

Without a way to test and measure some of the signals, you are working blind and have little hope, I feel, of finding the fault. Have you even checked the DC power voltages to the digital board?

[Tribble]

Thanks Ortec and Tony.

I'll check the sound tonight with a headphone.

I can borrow a multimeter with Hz measurement. Where should I check and what should I be looking for?

I did check voltages and I do seem to have power on the board where it should be but i'll do a better check now I have a schematic.

[ortek_service]

It's probably not worth trying to check for the sound output 'bong' on a DMM's 'Hz' measurement function, as it probably won't be a very-constant frequency.

So the 'Hz' measurement function will be best to use on the Horizontal drive signal (logic levels) output from the Digital board.
It seems on the Mac SE, this is a rather unusual horizontal line-frequency (compared to UK PAL 15.625kHz / CGA (& NTSC) 15.75kHz or VGA's double that of 31.5kHz) of 22.255kHz.

Detailed frequencies, on reply at: https://retrocomputing.stackexchange.com/questions/13077/wha...-of-the-lisa-and-original-macintosh

This webpage has some useful info about the SE's video circuitry:
https://tinkerdifferent.com/threads/mac-se-video-output-comp...not-tall-enough-skipping-rows.2937/


I presume you have the schematic as a pdf, so if you can attach a copy (Zipped-up if required, to reduce size / avoid forum compressing) / a link to it online, then can probably advise further where to probe for this signal.

Although I have a feeling the problem will be a bit more fundamental and that the CPU / ROM / RAM etc isn't actually functioning. And (like with Commodore PET's), there may need to be quite a bit of in-depth fault-finding of those areas to make much-progress, which you probably need at least a logic-probe (ideally an oscilloscope) - Although these can be obtained relatively-cheaply these days.
However, all supply voltages to these can be checked to start with, using just a DMM etc.

[Keith956]

Have you had a look at this? Has some guidelines on what to check if a black screen with no 'bong' on startup.

[ortek_service]

Originally Posted by Keith956

Have you had a look at this? Has some guidelines on what to check if a black screen with no 'bong' on startup.

That's quite a useful document - especially as the webpage it seems it was printed-from no longer exists where it originally was at: http://www.biwa.ne.jp/%7Eshamada/fullmac/repairEng.html

In summary, it suggests when there is a black screen with no signs of start-up

When the SE/30 appears totally dead (black out monitor, no startup bong, no spinning sound, no noise), the major cause of the problems is the power supply (SONY or ASTEC). Check the power supply/power switch with a digital multimeter. If the power supply doesn't work, replace it with another one (new or used)

So measuring ALL of the outputs of this PSU should quickly confirm whether that is at fault (although possible that these all measure OK at DC, but there is excess ripple on some due to failed electrolytics etc)

[Keith956]

It came from here, there are also schematics which may be useful:

https://www.macintoshrepository.org/875-macintosh-se-30-schematics-and-repair