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Author Topic: Enterprise 64 Video issue (Read 959 times)

Offline Prefim

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Enterprise 64 Video issue
« on: 2022.September.22. 17:02:14 »
Hi All,

New member, pointed here from a facebook group.

I have an enterprise 64. It initially had really shaky video via the monitor port and a scart cable from Retrocables. I was advised to adjust the L2 variable inductor which slowed the shaky to a very slow wobble (sometimes I can get it static) but there's still an odd bend to the image (see attached). I've reacapped the board and checked and have 10.3v input to the regulators and 5.03v output (measuring elsewhere on the board I see around 4.95V).  Any suggestions as to what the issue might be? the image on RF was straight and looked pretty good for RF.

I have the scart fed into a scart to HDMI which is confirmed good. when I plug scart direct to several TVs it fails to lock and produce an image.

Offline Dr.OG

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Re: Enterprise 64 Video issue
« Reply #1 on: 2022.September.22. 17:56:08 »
Does the SCART cable contain the recommended resistors? (See at the bottom of this page): http://enterprise.iko.hu/pinouts.htm
ÉN ekelek, TE keregsz, Ő gyeleg,
MI ákolunk, TI vornyáztok, ŐK lendeznek.

Offline Prefim

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Re: Enterprise 64 Video issue
« Reply #2 on: 2022.September.22. 18:04:10 »
It does. 100ohm on the mains lines and I forget the other but yes. I took the cable apart and checked that.

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Re: Enterprise 64 Video issue
« Reply #3 on: 2022.September.22. 21:41:56 »
Checked all the pinouts on the scart end. added some grounds next to red/green/blue etc. just to be sure. still no better. I can get a non-moving screen, but its still got the bend on the image.

Tried scart direct again to several screens some older than others. Saw something of an image one time but it was wobbly again.

Offline Judge

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Re: Enterprise 64 Video issue
« Reply #4 on: 2022.September.24. 08:28:20 »
I've reacapped the board and checked and have 10.3v input to the regulators and 5.03v output (measuring elsewhere on the board I see around 4.95V).
I suggest you check that the 12V voltage is correct.

29417-0  29419-1
Üdv.Judge

Offline Prefim

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Re: Enterprise 64 Video issue
« Reply #5 on: 2022.September.29. 14:10:17 »
Will check that out. thanks for the heads up. I didnt realise there was a 12v reg on there too. just the two 5v on the heatsink...

Offline Prefim

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Re: Enterprise 64 Video issue
« Reply #6 on: 2022.September.29. 19:55:57 »
@Judge

So I'm getting 7.73v on the right side as you marked out that 7812 reg.
9.38volts on the left side which I assume is the input
And if I measure the outer of the DC barrel and use the same ground point I get 10.12v

PSU lists output as 9.5V 2A output. So how are they getting a 12V regulator to regulate?. the centre pin of the regulator appears to be a dead short to other grounds.

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Re: Enterprise 64 Video issue
« Reply #7 on: 2022.September.29. 20:42:45 »
Here's a pic showing the voltages I get all over that section.

Offline BruceTanner

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Re: Enterprise 64 Video issue
« Reply #8 on: 2022.September.29. 22:54:09 »
PSU lists output as 9.5V 2A output. So how are they getting a 12V regulator to regulate?
It is a 1980s style DC-to-DC converter https://en.wikipedia.org/wiki/DC-to-DC_converter.

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Re: Enterprise 64 Video issue
« Reply #9 on: 2022.September.30. 02:11:20 »
So I'm getting 7.73v on the right side as you marked out that 7812 reg.
9.38volts on the left side which I assume is the input
Then the TR2 are dead.
Faulty C9 kill this transistor. Very common problem.
If you not replaced the capacitors then replace first, then the transistor.

Offline Prefim

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Re: Enterprise 64 Video issue
« Reply #10 on: 2022.September.30. 08:45:54 »
Thanks for the guidance and confidence on the TR2 being the issue. I've now got some on order (got the BC212 and BC337 just in case) and will get that fitted in a few days when they arrive. Hopefully I can have a nice stable, straight image then!

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Re: Enterprise 64 Video issue
« Reply #11 on: 2022.October.07. 13:13:49 »
Just wanted to say a big thanks for all the guidance. Swapped TR2 and saw 11.69v on the output of the 78L12. Still wobbling.
Swapped TR3, a BC212 with a BC212L assuming they were the same. Saw wobble and voltage dropped to 7v out the regulator.
Swapped back to the BC212 original in TR3 and voltage went back to 11.69v so clearly a BC212 and BC212L are not the same, then readjusted the variable inductor and got it bang on stable!

Now to investigate the ram upgrade and SD card options!
« Last Edit: 2022.October.07. 22:24:35 by Prefim »

Offline Quickie

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Re: Enterprise 64 Video issue
« Reply #12 on: 2022.October.11. 00:51:10 »
Excellent news, another EP64 alive and kicking! :)