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Author Topic: EP64 after few starts no screen over modulator (Read 456 times)

Online rambrand

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EP64 after few starts no screen over modulator
« on: 2020.November.21. 22:34:51 »
Hi,
i´m new for the Enterprise and get one from egypt a few days ago. First tests were fine, only the keyboard membrane seems to be defect, so I ordered a new one.

Now I received the membrane, but before replace it, I turned the EP on. The power led is lights up. But there is no picture on the tv.
Because I connected another retro computer to the tv i started a new channel search, but the tv doesn't find any signal from the EP.

My research showed that there might be an issue in combination with the 12V power supply and the capacitor C9. But I'm not sure, because the EP is absolutly new.

Does anyone have a hint for me? I have not a rgb cable (ordered one but not received it yet), may I get a signal over the monitor connector?

Hope my english is good enough to explain my problem ;-)

Bye
Markus
"Nukular. Das Wort heißt Nu-ku-lar." - Homer Simpson
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Offline ergoGnomik

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Re: EP64 after few starts no screen over modulator
« Reply #1 on: 2020.November.22. 09:12:57 »
I'm no electronics expert but that machine is not new at all. All these computers are well over 30 years old even if they spent no time turned on since manufacturing and quality control. And there could have been nothing done to avoid natural component decay.

It is a well known phenomenon that the electrolytic capacitors in these machines are prone to drying up. Your best move would be replacing all these in your computer without a second of thinking. Extra care must be taken when replacing the notorious C9 which is seemingly implanted with reverse polarity. You should replace it with a unipolar one or solder it with the same polarity as the one being there.

Furthermore, you should be prepared to replace TR2 too as it can break when C9 breaks down. It is also possible that L1 needs replacement too, in worst case.

These are based on the experiences of a well known amongst us Hungarian Enterprise guru frequenting this forum with Zozosoft handle and some other knowledgable guys.

Offline SlashNet

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Re: EP64 after few starts no screen over modulator
« Reply #2 on: 2020.November.22. 09:28:45 »
Composite B/W signal you can take from monitor connector.

Central male connector (RCA) connect to A3 contact, and ring connector to A2 or B2 contact: http://enterprise.iko.hu/pinouts.htm

Online gflorez

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Re: EP64 after few starts no screen over modulator
« Reply #3 on: 2020.November.22. 15:18:21 »
Better wait for the RGB cable before opening the Enterprise. Bad RF output is not a proof that your EP has a failure.

Does the speaker sound when you press the keyboard keys?
« Last Edit: 2020.November.22. 15:50:49 by gflorez »

Offline Zozosoft

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Re: EP64 after few starts no screen over modulator
« Reply #4 on: 2020.November.22. 16:45:15 »
Yes, it is very likely that capacitor C9 is faulty, which is killed the TR2.
Probably all egyptian EP64 with the bad Philips capacitors, and stored in a hot Egypt for a decades...

You can check the 12V output on the monitor connector, if it is less than 12 then this is the problem.
(With a RGB cable and old full analog CRT monitor you can got a broken, running screen in this situation, but modern TV/monitor say No signal or Invalid signal)

Online rambrand

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Re: EP64 after few starts no screen over modulator
« Reply #5 on: 2020.November.23. 23:10:50 »
Hi,

@ergoGnomik: yes i´ve read about the C9 and the possible death of TR2, when C9 dried out. That´s a realistic scenario.

@SlashNet: I´ve seen the page with the pinouts. May I make a Adapter for composite.

@gflorez: no the EP don´t makes any sound when pressing a key.

@Zozosoft: Thanks for info. I looked at the pinout of the monitor connector. But I can't find a lane with 12V. Where I can check 12V on the monitor connector?

Bye
Markus
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Online gflorez

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Re: EP64 after few starts no screen over modulator
« Reply #6 on: 2020.November.23. 23:30:01 »
If the speaker does not sound at keys pressed... The EP probably can't boot.

This picture is from Zozo's useful Enterprise page:



At the right you can see the representation of the Monitor/Audio EDGE connector, very near to the RF output connector you have been using.

The view is from the rear of the Enterprise(all the computer connectors have B=components side up, A=solder side down, numeration starting from the left of the viewer.

You must test with a multimeter the voltage between pins B2(GND) and B6(+12v).
« Last Edit: 2020.November.23. 23:33:12 by gflorez »

Offline Judge

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Re: EP64 after few starts no screen over modulator
« Reply #7 on: 2020.November.23. 23:49:03 »
@Zozosoft: Thanks for info. I looked at the pinout of the monitor connector. But I can't find a lane with 12V. Where I can check 12V on the monitor connector?

25829-0
25831-1

Inside the machine:

25833-2
Üdv.Judge

Online rambrand

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Re: EP64 after few starts no screen over modulator
« Reply #8 on: 2020.November.23. 23:55:50 »
Thanks, I´ll test the 12V on the connector.

Bye
Markus
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Online rambrand

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Re: EP64 after few starts no screen over modulator
« Reply #9 on: Yesterday at 22:39 »
Ok, got 11,8V at the monitor connector.
But no click sound when pressing a key.

Bye
Markus
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Re: EP64 after few starts no screen over modulator
« Reply #10 on: Today at 10:41 »
If I were you I would wait for the RGB cable before continue. Maybe you have the membrane totally dead...