Today, after repairing it, I dumped the PALs from a Sega Mega Play PCB.There were six devices, I was able to reverse three of them, one was already dumped by Porchy from a Mega Tech PCB.The remaining two use latches so a deeper analysis is required.
My friend Joachim sent me this Mega Play system for a repair:
The Mega Play is the name of a JAMMA-based arcade boardwith the ability to run Sega Mega Drive games. It was the second attempt by Sega to bring the home console to the arcades, following the Mega-Tech arcade system.Games come in form of cartridges:
At power up the system booted but got stuck on the welcoming screen not loading cart in whatever slot was inserted:
As I said, this system operates on the same core components that the Sega Genesis uses (plus some additional hardware, such as an additional Z80 and Master System VDP for driving an optional second monitor that displays a list of games installed).In particular there are two VDP (Video Display Processor) custom chips marked ‘315-5433’ and ‘315-5313’.When I went to inspect them, I found some lifted pins on the latter :
In particular lifted pins were some from 55 to 70 which are directly connected to the 68000 main CPU data bus :
I reflowed these pin and this was enough to fix the board:
Today we have an important Sega PLD update.After verifying the Out Run dumps we had (having confim they match the ones from my board) I was able to reverse and successfully tested into GAL18V10 devices two of them (original chips were one CK2605 and one PLS153).
Always in Sega, I dumped and successfully tested into GAL devices four PLDs (three CK2605 and one PLS153) from an original Fantasy Zone PCB on System16A hardware.
My friend Alexander sent me this original Sega Out Run PCB for a repair:
After adapting it to JAMMA I powered it up and I could noticed the defect :
There were some dots on the screen in which I could recognize parts of sprites (lile a ghost images, I’d say).Since video board is the lower one, I could not reach with my logic probe or scope the involved circuitry made of the 315-5211 custom Sprite Generator plus sixteen 62256 SRAMs chips :
RAM test was successfully performed but didn’t cover all the chips :
So I went to piggyback each RAM chip and when i did it for the one @IC71, the issue was cleared:
Time to remove the chip and install socket:
Obviously the desoldered chip didn’t pass the test on my programmer:
End of job.
Another double Tube Panic PCB repair, with this so far fourth are the PCBs I repaired for my friend ‘robotype’ (you can find here the first log).Let’s start with first one :
As label said, sprites were totally missing:
Sprites generation circuitry is located on the video board.ROMs were all good so, due lacks of schematics, I went to test components with my HP10529A logic comparator.When I clipped a 74LS161 counter @E8, comparator reported troubles on all its output pins:
It failed the out-of-circuit test:
With a good IC fitted, sprites came back :
First board 100% fixed, let’s pass to the second one which was labeled with “BAD SPRITES” (it seems sprite issue is a common failure on all the Tube Panic PCBs) :
This was confirmed once powered the board up:
As in previous repair, I already knew where to look at.Sprites ROMs are located on video PCB in form of 8 2764 devices on a small piggyback board:
Data of these ROMs are latched by some 74LS273, when I went to probe with my analog scope the one @E20:
I found all outputs were bad compared to inputs:
The IC failed when tested out-of-circuit:
The sprites looked much better but still not perfect:
This is how it should be (MAME screenshot):
So I went to probe other ICs with my BK560A in circuit tester which reported trouble on pin 16 (output) of another 74LS273 @G9:
This was confirmed also by my scope, the output pin 16 was stuck low compared to its input pin 17:
Once desolder and tested out-of-circuit, the IC failed in that specific gate:
A good IC restored sprites:
Another Tube Panic (I hope the last…) fixed!