JAMMArcade.net – Page 149

Pang repair log #2

Jun 162015

Got a friends Pang PCB here for repair.
He had carried out the ROM swap (made by ArcadeHacker) to desuicide it but he had no output although we could hear it playing blind.
The board is very clean and a visual check revealed nothing.
On powering the board up I got this screen

I could also hear the board did play blind so that’s a good sign.
I like to make little schematics for boards when I’m working on them and they don’t have any available and I quickly came up with this.

I started probing back from the RED pin on the JAMMA edge connector and soon came to a RAM chip at location 8C. Probing this chip and its counterpart gave me some odd looking signals which I got suspicious about.
These chips are CXK5814 SRAM chips and they seem the be the most unreliable RAM by comparison.
One of the RAM’s had all its data lines stuck LOW while the other chips data lines were all dead despite all the enable lines working as they should and the address lines active.
At this point I was certain they were dead but one last test was to ‘piggyback’ a known good RAM chip on top of the suspected bad one. I chose the one with the dead data lines to avoid potential contention and I got a partial image on screen.

I desoldered both the RAM chips and replaced them. I didnt have any spares in my RAM bin but found a couple of skinny 6116 RAM’s on a scrap bootleg board.

Fitting these I now got this wonderful sight.

Job done.

Olivetti Prodest PC1-HD (HDD version) PAL dump added

PAL Updates Comments Off

Jun 132015

As announced some days ago, we have another (and last) dump from Olivetti Prodest PC1-HD (the hard disk version).Binary dump of original PAL16L8 device was provided by José G. (JP-Retro ,JOSÉ GONÇALVES E PAULO SOUSA Group) and we took care of reversing its equations into a GAL16V8 replacement.Dump has been tested as working by José G, thanks to him and all other guys of Olivetti Prodest group.

Olivetti Prodest PC1-DFD (double FDD version) PAL dumps added

PAL Updates Comments Off

Jun 082015

In the past days me and Porchy were contacted by José G. (JP-Retro ,JOSÉ GONÇALVES E PAULO SOUSA Group).They are a group of “aficionados” of Olivetti Prodest PC1, a vintage home computer released in the 1988.You can read more about it here:

https://www.seasip.info/VintagePC/prodestpc1.html

There is a Facebook group as well:

https://it-it.facebook.com/OlivettiProdestPC1

He asked us for some help to reverse some secured PLDs (PAL16L8) present on the motherboard of his Olivetti Prodest PC1-DFD (double FDD version) :

So, we suggested him to build a simple adapter (designed by Charles MacDonald, all credits to him) to read them as 27C020 EPROM in a regular programmer:

He succeeded to get the proper binay 256KB dumps so we took care to analyze them and reverse their equations into GAL16V8 replacement devices.Dumps have been successfully tested by José G.

Thanks to him and long live to the Olivetti Prodest PC1!

P.S.

There is a third PAL to be dumped and reversed , this one comes from the HDD version of Olivetti Prodest PC1:

Chip is on the way to be delivered to José G. so stay tuned for further update.

Major Title (IREM M82) PAL dumps added

PAL Updates Comments Off

Jun 072015

Today, after repaired it, I dumped the four PAL16L8 on a Major Title PCB (which runs on IREM M82 hardware).The one marked “MT_A-2H-” @IC5 has same equations of the ‘M81_A-2H-‘ dumped (and tested) by Porchy from a M81 X-Multiply PCB, all other ones seem to be exclusive to this game but could be also shared with other IREM games.All dumps have been successfully tested in GAL16V8 replacement devices.

Major Title repair log

PCB Repair Logs, Repair Logs Comments Off

Jun 072015

Many of you may think that repairing arcade boards is a difficult task but sometimes it’s not so (well, few times though…).Here is an example.

Got an IREM Major Title PCB (M82 hardware) from my friend Corrado (who is part of JAMMArcade team as contributor):

When I powered it up I was greeted from this rolling screen:

There was no SYNC at all.I traced this signal back to a 74LS32 @IC14 on video board but, after checked its logic, it seemed good.I noticed there were some socketed ICs both on CPU and video board.Two of them were TBP24S10 PROMs manifactured byTexas Instruments (you can read its specifications in our “datasheet” section).When I pulled of the socket the one @IC47 I got this:

PIN16 (VCC) was broken so IC was not powered at all.A little bit of “reconstructive surgery” on this (other adiacent wobbly ones) pin was enough to restore the correct video syncronism (later I found that outputs of this PROM were connected to a couple of custom ICs involved in video timing generation).

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