PCB Repair Logs – Page 39

Michael Jackson’s MoonWalker repair log #2

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Sep 072017

Got this Michael Jackson’s MoonWalker PCB (Sega System 18) for repair:

Board booted but sound was missing at all and game behaved strangely, you could no longer move your character whenever you pressed the buttons or being hit by enemies :

At first glance I thought the FD1094 custom CPU module was slightly suicided so I swapped it with a good one along with the i8751 MCU but with no luck.I began to think of a correlation between the lack of sound and freeze.Probing the Z80 sound CPU revealed /HALT line was asserted while the /INT was floating.The latter comes from one of the two YM3438 FM sound generator @IC88 :

I removed the chip and tested it on a good motherboard, it was bad.But replacing it made no difference, the shared data bus of the two YM3438 was still inactive.So I pulled the other one @IC87:

It was bad too.Replacing it fixed the board.

Rainbow Islands repair log #11

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Aug 262017

This is the eleventh repair log for Rainbow Islands, almost a record for a board…

PCB was in fair conditions :

But the TC0070RGB DAC module was missing and its solderside was brutally burnt during removal :

Hence, for first I soldered back a spare module and patched a burnt trace:

On power up I was greeted by a blank static screen, /HALT and /RESET lines of 68000 were continuously going high/low sign that the watchdog circuit was active:

Usually this means that main code is not properly executed due some problems in CPU/RAM/ROM circuitry.For first I focused on WORK RAMs, two Sony CXK6864 (6264 pin to pin compatible).When I piggyback the one @IC26 I got this screen:

The watchdog shut down too, this lead me to remove the chip, it failed when tested out of circuit :

Now I got always that garbage screen.Probing the two 62256 RAMs @IC-IC4 in tilemap generation circuit revealed unhealthy signals on some data lines (good signal on the left for comparison)

Piggkybacking both RAMs at same time allowed the game to boot although with scrambled backgrounds:

I desoldered the RAMs having confirm they were both bad:

Graphics was perfect now but sound was faint and scratchy:

I used my audio probe to troubleshoot the sound circuit.This revealed that sound came out from PIN12 (which is the analog output to the TL074 OP-AMP) of the YM3012 DAC already corrupted.Indeed I could measure on this pin a weak voltage :

But a bad output means also a bad input and PIN11 (the analog input) was not healthy too:

This came from pin 8 of the near TL074 OP-AMP (through a 560 Ohm resistor)

I pulled it and it resulted faulty when tested :

Fitted a good OP-AMP restored the sound and fixed completely the board.

Sky Kid repair log

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Aug 252017

A quick repair for this Sky Kid (Namco) I received some days ago :

Board was in near mint condition but it didn’t boot sitting on a semi-static garbage screen (which was looping sign that watchdog was active)

Most of the devices were socketed so for first I ruled out the many custom ICs present, they were all working.Then I tested the RAMs out of circuit.Two Mitsubishi M58725P (2k x 8-bit static RAM) failed (at different address location)

Replaced them with compatible 6116 and board successfully booted with no further issue.Job done.

Mahou Daisakusen repair log

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Aug 222017

A friend got a Mahou Daisakusen (japanese version of Sorcer Striker) board with faulty graphics.

It was playing fine with sound but there was an obvious color palette problem.

I started looking at signals around the color outputs of the PCB and quickly found weak signals on the 74HCT273 at location U12. Piggybacking the chip with a working 74LS273 fixed the colors immediately.

I replaced the chip… Board fixed.

Here is a picture of the PCB with the defective chip highlighted in red:

Irem M92 double repair log #2

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Aug 172017

Received some Irem 92 boardsets mostly for replacing preventively the infamous ELNA brown electrolytic capacitors but two of them were faulty too.

The first was a Cross Blades (japanese version of Blade Master!), board had green ELNA capacitors so no strict need to replace them.

But it suffered from sprites isssue, they were missing some parts:

Pressing the board in the area of ‘NANAO GA22’ custom ASIC restored the sprites :

A closer inspection of this custom revealed three liften pins :

Reflowed them fixed the issue :

The second board was Hook (World version) :

Game booted up but sound was missing, I could hear only a rustling noise.Besides, video had some interferences:

Usually the two issues are strictly related, the cause is some bad electrolytic capacitor in audio circuit which affects video output too.The board mounted ELNA brown capacitors which are well known to age poorly.Sure enough :

The 470uF 25V @C202 was clearly leaking, this capacitor is used as filter for the +12V for the amplifier, this explained the issue.Measuring it out of circuit confirmed it was bad with an increased ESR of 150 Ohm :

I replaced this and all other electrolytic capacitors, this fixed board completely:

Here’s for reference the capacitors list with value and location :

C201 1uF 50V
C202 470 uF 25V
C203 220uF 10V
C204 22uF 25V
C209 100uF 25V
C210 1uF 50V
C213 47uF 16V
C215 1uF 50V
C216 1uF 50V
C217 1uF 50V
C218 1uF 50V
C219 1uF 50V
C236 100uF 25V

You can find it in our document section too :

https://www.jammarcade.net/files/Documents/Irem_’M92-A-B’_CPU_board_electrolytic_capacitors_list.pdf

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