PCB Repair Logs – Page 93

Nova 2001 repair log #1

Jan 312015

I got this pcb in December 2014 from Smitdogg of Mameworld as not working:

It was in good condition but it had already some TTLs replaced (socketed)

After firing it up I got a static coloured screen.

The Z80 was socketed so I first tried to replace it and to my surprise the game started apparently without any major faults with correct colours.

It was too good to be true and infact when the demo play started I got a very peculiar fault:

The background colours changed alternating between correct and not only during horizontal scrolling. During vertical scrolling the colour of the background was fixed in the last state (being good or bad).

I started the test of the pcb and everything looked good except the color check.

The “Back” had some strange colours which didn’t look correct

I decided to start Mame and see the same screen on the emulated game and I got this:

it seemed that there were some fixed bits on the background colours but that didn’t explain the alternating colours.

I looked for Nova 2001 schematics which luckily were available.

This game has plenty of 4116 drams which are prone to fault normally but they weren’t related to the fault I had.

I probed also the 3x 6116 SMD rams responsible for the background colors and the related 74LS273 buffers and they were all good.

At this point I had no clue where to probe, the schematics were really bad scanned and difficult to read.

I asked an advice to Charles MacDonald which pointed me to look on the AY8910 sound chips whose I/O are responsible for the horizontal and vertical scrolling.

The first 3 bits BH0, BH1 and BH2 of AY8910@1,2A are negated and sent to a series of 74LS151 @12U, @11U, @10U and @9U.

All the signals going to these 74LS151 were good.

I probed the outputs of all the 74LS151 and noticed that the TTL @12U was oscillating in sync with the alternating background colors.

After checking the inputs of this chip, I noticed 3 stuck signals which were back traced to the 74LS164@12T whose inputs CLK and CLR were correct.

Changing this TTL restored the correct colour of the background during scrolling.

Pitfall II repair log #2

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Jan 302015

The ‘F’ curse strikes again!

This could be a perfect title for this repair log but let’s start from the beginning

Got this faulty PCB from a friend:

It had sever issues, only most parts of graphics were missing and colors were clearly wrong while sprites barely visible

After studying the hardware I could identify the tile RAM in two MB8128 (2018/6161 compatible) chips @IC73 and @84.Probing them revealed irregular actitvity on some address lines.Piggybacking them with a good chip didn’t change anything.I could trace these address line back to the outputs of some 74LS157 multiplexers.Testing them with my HP10529A logic comparator gave me faults on three of them which I promptly desoldered and tested out-of-circuit having confirm they were all bad:

This improved graphics so that I could clearly also see the results of the ROM/RAM test:

IC73 and IC84 (tile/backgrounds RAMs) were riported still bad as well as the color RAM @IC85 so was time to investigate deeper.

Data bus of the color RAM (a 2016) was connected to a couple of 74LS175.Piggybacking the one @IC108 restored colors while piggybacking three 74LS245 @IC104, @IC105, @IC106 (involved in tile RAM data bus) restored most all the graphics and also the RAM/ROM test passed succesfully:

But there was another issue (see picture below):

To cut the story short I found another faulty 74LS157, one of them that I previously tested as good has gone bad while I was troubleshooting the board!Replaced it fixed completely the PCB.

Ah, I forgot…all faulty TTL ( nine in total : four 7LS157, one 74LS283 -not reported in this log-, one 74LS175 and three 74LS245) were manifactured by Fujitsu! Of course, the curse stroke again but I pushed it back! 🙂

Violent Storm repair log

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Jan 252015

Got this faulty Violent Storm PCB from Ebay (well, actually seller sold me as Metamorphic Force one…)

When I turned it on all I got was a solid black screen but this time watchdog circuit was not active.As many other Konami boards RESET signal is generated by PIN10 of the SIL custom ‘051550’.In this case signal was correct (first LOW then HIGH) but not on main CPU (an MC68H000GFN16 in PLCC package) where it was stuck LOW.So was time to investigate.I could trace RESET signal from PIN10 of the ‘051550’ custom to PIN7 of a custom marked ‘053252’ (44PIN in QFP package) while , from other side, RESET (PIN18) of the main 68000 CPU was tied to PIN12 of this ‘053252’ IC through some inverter gates (74F04).This was confirmed also by Metamorphic Force schematics (which runs on same indentical hardware) I could find at a later time:

As I said RESET signal was correctly generated by ‘051550’ custom, routed to ‘053252’ ASIC but then coming out from it stuck LOW.So with this assumption I had no other way than try to replace the ‘053252’ ASIC (in MAME source it’s indicated as CRT and interrupt control unit):

And I was right since board successfully booted and all was properly working:

I was closing the case and declaring the board 100% fixed but the curse of the Konami hybrid sound module struck again!Infact while I was testing the board, the sound suddenly faded.But this time it was not only matter to replace all the SMT caps with tantalum ones but also the LA4705 audio amplifier broken due high ESR of the old caps and we all know that capacitors have the role to stabilize amplifier preventing its oscillation and failure:

That’s all for today, I hope you enjoyed this repair log!

Rainbow Islands repair log #6

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Jan 212015

All good things come in threes!

Yes, this is the third Rainbow Islands PCB (the fourth if we include the Extra version) I repaired.The PCB was in good state (dust apart):

But all I get was a solid blank screen upon powered it on, no activities on DATA/ADDRESS bus of 68000 CPU, RAM and ROM.The program ROMs were dumped as good so I went to the two 6264 WORK RAMs @IC25 and @IC26 and, mindful of what had already happened with the other Rainbow Islands PCBs, I desoldered them and tested out-of-circuit.Both were bad!

With new WORK RAMs fitted the board sometimes booted stuck on “OBJECT RAM ERROR” other times with jailbars all over the sprites:

Jailbairs are a clear symptom of wrong written data.Sprite generation circuit on this PCB is made of a PGA custom ‘PC0900J’ , four 2018 SRAMs , some latches and buffers.Piggybacking the RAMs had no effect but when I made it on a 74LS244 @IC15 the jailbars faded and then disappeared completely when I piggybacked the other 74LS244 @IC17.

Desoldered them and tested out-of-circuit confirmed they were both bad:

Graphics were perfect at this point.Last issue to troubleshoot was the absolute lack of sound.When I was gonna to analyze the sound circuit I noticed @IC44 the 6264 RAM of the Z80 audio CPU was already socketed so I decided to test it resulting in a bad chip.Replaced it restored the sound.Board 100% fixed!

G.I. Joe repair log #2

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Jan 142015

Yes, yet another G.I. Joe PCB on the bench (this is the third I repair).Let’s start with the log.

PCB was in a clean state:

But, as often happens with this Konami hardware, board had the watchdog active sign that there was a problem in main code execution or in the CPU itself.As usually I started my troubleshooting analyzing the main 68000 CPU and I found that, though the RESET signal was correctly generated by the custom ‘051550’ and reached the CPU, PIN17 (/HALT) and PIN18 (/RESET) of 68000 were stuck LOW so it was not never inizialized (all control lines were obviously silent ,too).So, judging from this,I started to suspect that 68000 was really faulty.I decided to do an “extreme” piggybacking with a good know CPU and sometimes I got it booting showing a bad color RAM:

This was enough to desolder the main 68000 CPU (a 16MHz one manifactured by ST) fitting a proper 64PIN socket:

Trying it in another board I obtained a solid black screen sign that it was realy bad (it’s the first time I came across a faulty 68000 CPU, never happened before).With a new 16MHz 68000 fitted in the socket board succesfully booted always showing the color RAM error above but I quickly fixed this by replacing both 2018 SRAM (also the one @14C was bad)

As I expected in this kind of Konami hardware which use ‘054986A’ hybrid custom sound module there was absolute lack of sound ,only some popping noises sign that the LA4707 amplifier was still alive at least.So was time to replace all the SMT electrolytic capacitors with new tantalum ones as they were leaking and having ESR value out of specs:

and install proper 1.778mm pitch sockets for the module to finish the job:

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