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Author Topic: JoPac JO7400 not working  (Read 1272 times)
Little_Rabbit
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« on: January 18, 2018, 11:07:32 PM »

Hi guys,

I attached more pictures of my unusual JoPac (sorry for the low quality pictures, I took them yesterday with my phone in my storage room where light is not good...).

I first noticed this unusal switch under the console. I opened it and it revealed to be simply the power switch because the original one is missing (broken I imagine).

As I said before, there's absolutely no name, brand or product reference on it ! Because I'm not a Videopac expert, I discovered only very recently that it was a JoPac Smiley.

The nice thing is it features an RGB output with a SCART cable Smiley.

This evening I brought it back home, so I will be able to look closer at it, and will start to repair it. On the next post I'm gonna show you some of the cartridges and the inside, and the defect Wink.

Bye
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Little_Rabbit
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« Reply #1 on: January 18, 2018, 11:25:06 PM »

Hi,

Here are some of the cartridges I got with the console.

As you can see, many of them were opened and somebody hand-wrote extra numbers on the label.

Bye
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Little_Rabbit
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« Reply #2 on: January 18, 2018, 11:30:32 PM »

Let's have a look inside Smiley.

Do you know if most the G7400 pcbs have their main chips mounted on sockets ? Does this PCB look standard to you ?

As I said, it doesn't work : when I put a cartridge and turn it on, I get garbage and glitches on the screen, sometimes some sound effects. If I press the RESET key, I get the "Game Select" invitation screen, but corrupted.

If you look at the letter I get, you will notice it is written "WELEGT GEME" Smiley.

Let's have a look at binary coded ASCII table for the impacted letters :

S = 01010011
W = 01010111

A = 01000001
E = 01000101

C = 01000011
G = 01000111


Have you noticed the same thing as I noticed ? Smiley

The third bit from the right, D2, is always set to 1 on my machine, even when it should be set to 0 !...

I need to look at the data bus and find wich component is defective, forcing the data bit D2 to a high level. If you have any clue, it would be very welcome Kiss.

Bye
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Janzl
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« Reply #3 on: January 19, 2018, 08:17:20 AM »

I can't help you with the technical side of this story but I do notice that the character colors on your Select Game screen are different than the standard colors. Might be just the photo but I'll post an image for comparison just in case.

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gertk
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« Reply #4 on: January 22, 2018, 08:10:17 PM »

If the chips are socketed you might try to pry them a bit out of the socket and press them in again, might do the trick.
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Rene_G7400
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« Reply #5 on: January 23, 2018, 09:51:10 AM »

It's normal for a Jopac console that the large chips are socketed.
Normally the start-up screen of a Jopac displays "Quel Jeu ?" instead of "Select Game".
I noticed that this Jopac console seems to be missing the Secam modulator PCB.
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Little_Rabbit
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« Reply #6 on: January 29, 2018, 05:49:17 PM »

Hi guys,

Thanks for your comments and hints.

@gertk : that’s the first thing I did, even before registering on your forum Wink.

@Rene_G7400 : Thanks for the info about the sockets ^-. Yes, you’re right, the SECAM RF part is not present! There’s only the SCART output on the mother board. As you can see on the picture, the soldering points on the edge of the PCB on its lower part look intact: I think the modulator was never soldered on this Jopac. I still believe it was a pre-production unit (no labels on it, no RF modulator, an English “SELECT GAME” boot screen instead of the French “QUEL JEU ?”, a Videopac keyboard overlay instead of a Jopac one).

So, I spent a little time trying to repair this Jopac. I first looked for the schematic: Google led me to the Rene’s page! ^- Thank you Rene for this precious information!  Cool

I have some general knowledge about systems built around 8 bit microprocessors, but I admit I was quite lost reading the Videopac schematics ! Smiley I knew nothing about the 8048 Intel family, so it was a new world for me!

As I said in a previous post, I noticed the 3rd data bit was wrong, according the misspelled “SELECT GAME” boot screen. With an oscilloscope, I looked at the bit B3 of the multiplexed bus: it was not dead; I could see some activity, changing from 0 to 1. It didn’t seem to be the track to follow…

I also checked the quality of the +5V powering the motherboard: it looked fine. To be sure, I temporarily replaced it with an external lab power supply (picture 1): same result.

I read more posts published on http://videopac.nl and noticed it was often said that most of the breakdowns came from the µP8048 itself !...

By chance, I have another Videopac+ in my collection, a Philips G7400 made in France, and in working condition! Smiley (picture 2, 3  and 4)

(next post for the rest of the story)
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Little_Rabbit
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« Reply #7 on: January 29, 2018, 05:59:02 PM »

I opened it and first noticed the motherboard looked exactly the same. I also noticed the huge SECAM RF module not present on my Jopac (attached picture 1 and picture 2).

I first swap the 8048 of the working one to the faulty Jopac. I first took the cartridge #19 (Catch the ball + Tic Tac Toe) for my test : it showed a garbage boot screen (picture 3). But, I discovered later this particular cartridge create the same buggy boot screen on a valid Videopac ! Cheesy Murphy’s law I guess Wink.

Even with the buggy boot screen, I noticed that if I press reset and then press 1 for example, it launches the game ! I tried another cartridge, and with this one, I got a buggy boot screen (showing “QUEL JEU ?” misspelled since I was now running a French µP 8048), and once again, I could play the game !

Then I tried a Videopac+ cartridge, the number 51 (Terrahawks, a pretty good game for the Videopac !) : buggy boot screen, like before, and this time the high res background picture was buggy too, but the game fully playable (picture 4, sorry for the bad quality Undecided).

My first conclusion was my µP8048 was dead, but a good one was not enough to make the console fully operational.

(next post for the rest of the story)
« Last Edit: January 29, 2018, 06:07:02 PM by Little_Rabbit » Logged
Little_Rabbit
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« Reply #8 on: January 29, 2018, 06:06:15 PM »

So I continue to swap the chip mounted on sockets, chip after chip to see if it made a difference :

- RAM MC6810 /IC653 => no change
- SRAM MSM2128 /IC IC671 => no change
- SRAM MSM2128 /IC IC666 => no change
- SRAM MSM2128 /IC IC667 => no change
- VIN CRT Display Processor EF9340 / IC661 => no change

Can you see my face becoming more and more desperate ?? Undecided Wink

And I swapped the little brother of EF9340, the Character Generator EF9341 / IC662 => bingo ! It was the guilty chip !!

Now Terrahawks plays just fine (picture 1).

To be sure this EF9341 chip was responsible for the buggy boot screen from the beginning, I put back the faulty µP8048 => the console doesn’t work of course, but I have at least the proper boot screen (picture 2) Smiley.

The results of this troubleshooting show that I have 2 faulty chips:
- Intel µP8048
- Thomson EF9341

Would some of you have some spare parts that you could sell to me? I imagine the 8048 can't be bought anywhere in shops because it includes the Philips boot code in its internal ROM, can it ?

Regarding the EF9341, I read on the Internet it was used in France inside the Minitel (a unique device provided for free by the French Telephone company, a communication terminal letting you consult some kind of BBS services in the 80’s/90’s) ! Smiley So it must be pretty common, but I have no source right now. If some of you have it at a low price, you could make my day Smiley.

Thanks for having read my (too long) story ! Wink
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VideopacBelgium
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« Reply #9 on: January 29, 2018, 07:52:51 PM »

Great technical story!
I have spare
- Intel µP8048
- Thomson EF9341
 Smiley
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Rene_G7400
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« Reply #10 on: January 30, 2018, 09:10:29 AM »

It's rare that two chips are dead at the same time.
Nice that you were able to find the problems!
The Minitel console contains an EF9345 chip.
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gertk
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« Reply #11 on: January 30, 2018, 07:03:15 PM »

As for the 8048, you can use a 8748 instead (8748 is the Eprom version of the 8048) You just need a suitable programmer.

I have a Digelec 844 824 programmer which can handle the 8748 and have already made some 'custom' versions of the G7000 and G7400 CPU's

8748's are still to be found on eBay
« Last Edit: July 02, 2018, 10:15:53 AM by gertk » Logged

>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
Little_Rabbit
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« Reply #12 on: January 30, 2018, 10:16:05 PM »

Hi,

Thanks a lot for your comments ! Kiss

@VideopacBelgium : Thank you very much Marc for your kind offer ! Let's see in pm if we can find an arrangement Cool.

@Rene_G7400: you're right, some Minitel use the EF9345 chip. But as far as I've understood from my quick reading, only the most recent ones use the EF9345. The older ones use the pair EF9340+EF9341.

@gertk : thanks for the info ! That's nice to know there's an alternative source, and that it can be programmed by ourselves. I've checked my Wellon VP280 programmer : unfortunately, it seems this programmer doesn't support the 8748 familly... Cry

Thanks again Smiley.
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Little_Rabbit
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« Reply #13 on: September 11, 2018, 03:40:51 PM »

Hi,

No, I'm not dead ! Wink

Sorry for not having given any news sooner... it's true this Jopac repair is not on the highest position of my to do list Wink.

For the ones remembering my quest, I was looking for :
- Intel µP8048
- Thomson EF9341

I knew the EF9341 could be found in a French Minitel : I finally found someone who mod Minitel to transform them as Bartop, and got his mother board Smiley. With my de-soldering iron, I succeeded in picking up the EF9341 ^- !
(picture 1)

For the Intel µP8048, I discussed a little bit with VideopacBelgium who could have it as spare parts, but unfortunately I had nothing to offer as an exchange  Cry. Thanks to the hint from gertk, I'm now looking for the EPROM version of the Intel micro-controler. My programmer is not compatible with this device, but a friend of mine has a Galep 5 that can do it ! Azn

Could you confirm that such a 8748 is the chip I need :

https://www.ebay.fr/itm/D8748H-INTEL-INTEGRATED-CIRCUIT-D8748H-DIP/201426424313?hash=item2ee5f351f9%3Ag%3ATcoAAOxyaoFSDi1M

Then, would you have a link to the proper binary file for its programming (an English version displaying "SELECT GAME" would be ideal to keep it as the original Smiley ) ?

Thanks a bunch for your help !
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