JAMMArcade.net – Page 184

Konami GT repair log

Jul 232014

A friend of mine sent me this really mint original Konami GT PCB saying it suffered from vertical stripes across most part of screen.

Fired up the board and …he was right 🙂

Initial test said all RAMs were good so the problem was elsewhere.Without any schematics I started my visual inspection as usual.I noticed that the only IC replaced on this mint PCB was a 74LS157 @H13.Since a socket was installed, I removed this IC and all the part of graphics affected by stripes disappeared so I started to think problem was generated after this part of circuit.In particular I traced an output (pin 7) of this 74LS157 to pin 4 (RAS) of some TMM4164 DRAMs (there are 16 of them).Probing these DRAMs with my logic probe revelaed that on four of them pin 2 (DATA IN) was pulsing but the pin 14 (DATA OUT) was stuck high.So I desoldered (they were @G2, G3, H4, H5 position) and test them in my Hi-Lo Systems ALL-07A programmer and the result was this:

They all failed miserably.I was lucky since had some good 4164 DRAMs taken from a scrap PCB in order to repair a Commodore 64 motherboard.Installed them and goodbye stripes for ever!Board 100% fixed.

Varth bootleg PAL dumps added

PAL Updates Comments Off

Jul 232014

This interesting CPS1 bootleg has seven PLDs, five of them are registered so I could dump only the two combinatorial ones.The first is a PALCE20V8H device that was dumped by me and reversed by Porchy in a GAL20V8 targeting device, the other was dumped and reversed by me into a GAL16V8.Both are tested and working.

X Multiply RAM errors

General, Technical Info 1 Response »

Jul 202014

At the moment I have an X Multiply PCB that shows a “RAM NG 10” error on startup.
Although I have yet to find the problem with this board I thought it best to find out exactly what RAMs these errors are referring to.
To make any sense of this you will need the memory map for the game found in M72.C file of the MAME source code.

Here is a short list of what I have found so far:
0x9c000-0x9ffff = RAM NG 1 (Work RAM)
0xc0000-0xc03ff = RAM NG 10 (Sprite RAM)
0xc8000-0xc8bff = RAM NG 9 (Palette RAM 1)
0xcc000-0xccbff = RAM NG 8 (Palette RAM 2)
0xd0000-0xd3fff = RAM NG (Video RAM 1)
0xd8000-0xdbfff = RAM NG (Video RAM 2)

Cheap and easy -5v

General Comments Off

Jul 152014

Its becoming more and more common for power supplies to not supply -5v.
There are devices out there like the “Negatron” that offer a nice and easy way to obtain an adjustable -5v but there is a much cheaper way of getting it providing you can do a little bit of soldering.
Intersil offer a 7660 voltage converter IC. Its an 8 pin DIP device that can be bought for under £1 from Farnell and other places.
Farnell – ICL7660

I bought a couple of these on a recent order to test and the results, as expected, are great.
This is it setup on breadboard.

All that’s required is a +5v input, the ICL7660 IC and 2 x 10uF capacitors to get a -5v output. Add a variable resistor into the mix and you have a fully adjustable device for very cheap.
Here is the diagram lifted straight from the datasheet to show how simple this is.

Gradius 2 PAL dumps added

PAL Updates Comments Off

Jul 132014

I dumped 3 PAL chips found in a Gradius 2 board set.
The board set is not fully operational so I have not marked them as tested in case one of these chips is at fault.
I have also dumped the PLS173 chip on this board but it looks very suspicious so I have not included it. If anyone has a dump of this chip or its equations I would be interested in seeing it.

Thanks

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