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Author Topic: EP repair service? :-) ... help with Egyptian EP64 -no video output/not starting (Read 702 times)

Offline John Fante

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Well! This is certainly not my sommer when it comes to EP :( . First I managed to mess my EP128 when I tried to fix a video problem. Now I can not get my "new" Egyptian EP64 to start. More on that later.

First: Are there anybody - besides ZoZo who is a bit out of the loop at the moment - who does EP repair work? I can solder a bit but I do not have the equipment or knowledge to fix major issues. I will ofcourse pay for the time, postage etc. I would highly appreciate it if anybody are willing to give it a go!

Secondly. The Egyptian EP64 problem (the 128 problem is described in the thread linked to above). The machine I recieved is in VERY good condition. Clean an clearly not used. The red led lights when I power it on and you can hear very low static in the speaker so there is some kind of activity. However there is no video output and there is no click when I press the keys so it is not booting.

There is also some kind of signal comming out of the RGB port. My OSSC registers this but no picture. Normally the frequency should be like this.

My first instinct would be the two voltage regulators (7805) to see if the machine is getting enough power. They are however fine. The next would be to recap the machine. Capacitors does not age well.

It would be a very big challenge for me to do a recap. Does anybody here has some advice on doing it and does anybody have a complete list of the replacement capacitors I need?  

Or is there any other suggestions/advice?

I have done a first check of the motherboard and it looks fine. You can see it here and a closeup of the power section here.

Sorry for taking your time with my issues. This has really been an EP sommer from hell. Instead of playing with my Symbiface3 as planned I have been bogged down with technical issues.

I hope someone will be able to help so I can get at least one of the machines up and running.

Thank you in advance!
« Last Edit: 2020.August.25. 13:44:00 by John Fante »

Online gflorez

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Sorry, I am not your guy...  But Zozo  always puts Philips capacitors as one of the common failures on the 64KB computers. And your EP64 already has Philips capacitors.....

Another obvious question: Have you tried the OSSC on other devices to reassure it works fine?

Edit: Reading the value of an electrolytic capacitor is very easy, as it is written on the cylinder.

If you have experience in soldering it will be very easy for you to do it.

Buy one of this:

I have tried some of them, and usually the cheaper is the best...  It works as a gun, you must arm the tool and then press the trigger when you have heated the tin on the hole with the point of your iron. Put the mouth of the de-solder pump near the hole you want to clean.

You have to be fast on the operation, you can't heat the hole for a long time(only a second or two every time), because then you can burn the cooper tracks.

Probably it will be better to train you on the PCB of a device you have thrown on the trash bin....

Also, electrolytic capacitors have polarity. Usually a "+" is marked on the PCB, but the capacitor makers put only a lot of  "-" on the negative pin.... Just the contrary pin. Better you must guide you by the pictures of your PCB, and change them one by one. If you test the video between every individual change, still better.

Some of the capacitors you will find on the EP have a pin on every side(axial, observe how the arrow marks the right leg on the picture as the negative),



not so common today, but can be replaced with the usual component with the two legs at the same side of the cylinder(radial). The pins are usually very long, so they can fit on the same holes than the axial type, but you must isolate one of them. If it doesn't reach the holes, solder a lead on one of the legs.



The values you will read on the capacitors will be a number followed by nF, uF or pF, nano Farad, micro Farad and pico Farad. You also will read a voltage, but it is only the maximum operation voltage, so 15v or 20v is good for the EP.
« Last Edit: 2020.August.26. 00:00:48 by gflorez »

Offline John Fante

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@gflorez: Thank you for your - as allways - huge help :) I will start soldering .... :smt068

Offline Judge

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I've already done this with an EP64 motherboard. Here you will find a list of capacitors in post # 98.
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Great!

You can also extract the capacitors gently pulling with your fingers from the component while you heat the tin on the hole from the PCB underside. Gently to avoid to break some cooper track. Once done you can use the vacuum pump to clean the surplus of tin inside the hole. The good point is that the Enterprise PCB was very well build and will endure the punishment.

Offline dangerman

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My first instinct would be the two voltage regulators (7805) to see if the machine is getting enough power. They are however fine. The next would be to recap the machine. Capacitors does not age well.

If the 5V is fine, have you got a volt meter and checked the 12V coming out of the 78L12 regulator? It could be that you're not getting 12V to the motherboard. Apparently the most common fix with 12V is to replace TR2 and C9.


Offline John Fante

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If the 5V is fine, have you got a volt meter and checked the 12V coming out of the 78L12 regulator? It could be that you're not getting 12V to the motherboard. Apparently the most common fix with 12V is to replace TR2 and C9.

I have not checked the 12V. Where is "78L12 regulator" more precisely located? :)

And thank you for the tip :)

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It's U21. Check out this photo.

Offline John Fante

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I managed (I think) to find the 78L regulator and have measured it :smt050 .

It shows 6,8 volt on the output pin and 8,3 on the input. I figure that that is not the correct value :)

I have changed the C9 capacitor and that did not make a difference so is the way forward to replace TR2 and maybe 78L12?

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If the voltage at input 78L12 is lower than 12V, it means that the converter is not working (probably TR2 failed).
Below is a diagram (description in the thread).

Offline dangerman

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I agree with Pear. The input voltage to the regulator 78L12 is too low, so I'd try replacing TR2

Offline John Fante

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It is alive :ds_icon_cheesygrin: :ds_icon_cheesygrin: :ds_icon_cheesygrin: :ds_icon_cheesygrin: Replacing TR2 brought it back to life.

The keymembrame is dead (simply fell apart) and need replacement and I have a little noise on the picture but otherwise it seems to be functioning.

I have - so far - only replaced three caps so maybe the noise problem is there but it this a known problem? Besides the noise the picture seems rock solid (and better that an my old 128)

Offline Judge

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The keymembrame is dead (simply fell apart) and need replacement...

You can also buy foil from the one I showed Getafix.
Quote
http://www.commodoreszerviz.hu/billentyuzet_folia.htm
This person is very nice, and very efficient.  Replied immediately and we had a few back-and-forth emails over the weekend.  The new keyboard membrane is in the mail to me already.  

At this time, the price before shipping was 8.000 HUF (EUR 23 and USD 27) which, in my opinion, is reasonable.  

I will report back once I have received the new keyboard membrane.

I think Philips capacitors are highly recommended to replace them all. You can read about it here:

Újrakondiztam egy EP64-es alaplapot. Már épp ideje volt. A 100uF-os kondik már csak 70-75uF-ot tudtak, a C9-es pl. már csak 65uF-ot.
A 10uF-osak mind már csak 7-8uF-ot. Mindegyik Philips volt.

Az Enterprise kondenzátor készlete (segítség annak aki hasonló műveletre vállalkozik):

3db 100uF 25v álló    (8x12mm)
3db 100uF 10v fekvő (6.3x11mm)
11db 10uF 25v fekvő (5x11mm)
Üdv.Judge

Offline John Fante

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I have allready written to http://www.commodoreszerviz.hu/billentyuzet_folia.htm regarding new membrames. Thank you very much for the tip/link :)

I have planed to continue replacing the caps while I wait for the keyboard membrame. Was just wondering if the "noise" problem was a known issue.

Offline Zozosoft

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    • http://enterprise.iko.hu/
But Zozo  always puts Philips capacitors as one of the common failures on the 64KB computers. And your EP64 already has Philips capacitors.....
Yes :ds_icon_cheesygrin:
Meanwhile John solved it. If the C9 failed, then it is kill TR2, as it is also happened there. Another capacitors not a "life-critical", but good idea replace all avoid signal noise problems.