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Old Tech Fan
August 4th, 2017, 11:43 AM
Hello there, I am having problems with there being no video on the screen on my Eagle ][e. I have
booted up the computer. I have verified it by typing commands and having disk response.

ldkraemer
August 5th, 2017, 04:30 AM
Bitsavers has the Service Manual in PDF format.

Page 55 is the place to start. Turn on the Computer and look for a glow of the CRT Element. If it isn't
glowing then it's the CRT Power Supply. There are other steps to follow if it is glowing.

Larry

Old Tech Fan
August 6th, 2017, 08:56 PM
Thank you, I googled and I got a huge amount of spam.

ldkraemer
August 7th, 2017, 04:30 AM
You got SPAM from going to Bitsavers? I doubt that.

http://bitsavers.trailing-edge.com/
http://bitsavers.trailing-edge.com/pdf/eagleComputer/


Download the Service manual.


Larry

JonB
August 7th, 2017, 05:56 AM
@Old Tech Fan: How much general purpose electronics know-how have you got?

Here's a few things to try. open up the Eagle and...


Look for the video connector and try to reseat it. Check the connectors for loose wires or dry joints. If it is an edge connector, try to clean the CRT PCB contacts.
See if the back of the CRT is glowing with the machine on.
Reseat the plug at the back of the CRT. WARNING - HIGH VOLTAGES. Turn the Eagle off and use rubber gloves. DO NOT DISTURB THE HT LEAD (big fat wire plugged into the side of the tube). It's got very high voltages, which can persist even after switch off as the tube can act like a capacitor.
Check the brightness / contrast controls (if fitted) - sometimes they can get dirt in between the wiper and carbon track (this can lead to a screen blackout). Turn them back and forward a few times.
Sometimes there are trimmers on the CRT board for brightness / contrast (instead of, or in addition to the user controls). Refer to the service manual to find them, then turn them back and forward (to clear any dust). Aim to leave them in the original position.
Locate the power supply to the CRT board and check it is within tolerance with a multimeter. Use the schematic in the service manual to locate it.



If these don't help you will be in the realm of trying to see if the video generation circuitry is working or not. You will need at the very least a logic probe, but better still an oscilloscope. Have you either?

Cheers
JonB

JonB
August 7th, 2017, 06:08 AM
From the service manual:

The monitor is a Motorola 12 inch monitor containing its own power supply and requires
only a single AC input (110 VAC, 60 Hz; or 220 VAC, 50 Hz). The video signal, horizontal
sync, and vertical sync are provided via a small ribbon cable from the main board module.
The monitor provides adjustments for the +24 volts, horizontal hold, vertical hold,
horizontal delay, vertical linearity, vertical size, master brightness, focus, and horizontal
width. Adjustment procedures can be found in SECTION 4: HARDWARE MAINTENANCE.

So, it is a single unit with its own PSU. If the CRT is glowing, we can probably assume the PSU is OK.

You can build a really small circuit to combine its inputs into a composite video signal. Something like this:

http://www.dasarodesigns.com/product/commodore-pet-video-mixer/

This is for a Commodore PET, true, but that machine supplies video, horizontal and vertical sync signals to its monitor like the Eagle does, so you should be able to hook it up to the Eagle and a composite monitor and see if the computer is producing a picture. The purpose of this is to determine if it is the Eagle main board or the monitor that is at fault.

The video mixer is very simple. You could knock one up on a bit of breadboard. Take a look at the original version: http://www.dasarodesigns.com/wp-content/uploads/2014/03/pet-composite-video-adapter.jpg and have a go. If it cost you more than a few quid (or dollars?) I'd be very surprised.

:)