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Rainbow Islands repair log #11

PCB Repair Logs Comments Off

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.

Commodore 1084-D repair log

Monitor Repair Log, Repair Logs 2 Responses »

Aug 262017

This fantastic monitor has been on my test bench for as long as i’ve been in this hobby and its been a great little work horse.
I powered it up the other day to test something and noticed the upper half of the screen had what I would describe as thick scanlines whereas to lower half of the screen looked a little compressed.
I hooked up my NES to it and the problem was a lot more apparent

Keep you eye on Luigi when he jumps to the top of the screen. As he moves up he gets longer

Asking a couple of people quickly, they all recommended changing the capacitors. The ‘shotgun’ approach isn’t really something I like doing as I like to understand what would cause issues before I randomly poke around but monitors are not my strong point so I started ESR testing in-circuit.
All the capacitors I checked were perfect with really low ESR values and all the capacitance readings were within spec. All except for one little capacitor, C306. This is a 47uF 25v capacitor and is connected to pin 12 of the vertical deflection circuit (TDA1670A)

I tested the capacitor out of circuit and confirmed for sure it was actually bad.

With the monitor taken apart I hooked up the Muter BMR95 to the tube to check the condition of the guns
A tube can usually be identified by the label that is on the back of the tube

E2940B22 is the one we want. Next we cross reference this to the supplied manual to find which adapter we need to use.

Adapter 808 is the one we need for this tube.
All hooked up

The guns aren’t too bad and certainly no need to attempt any cleaning or rejuvenating. Sometimes this can cause more harm than good. I have a spreadsheet prepared too as outlined in the BMR 95 manual to give a better indication of the life expectancy of a tube but i’ve not included it here.

With all that done it was time to test the monitor again

All seems to be fixed again and im happy with that.
You can see the stretching better with a picture comparisson

Before

After

Never underestimate the importance of a single capacitor!

FixEight PAL dump added

PAL Updates Comments Off

Aug 252017

‘Rod_Wod’ sent in dump of the unique PAL from a FixEight PCB.Original device was an unsecured PALCE16V8H, dump has been successfully tested by him onto a same device and a GAL16V8 too.Thanks again to him.

Sky Kid repair log

PCB Repair Logs Comments Off

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

PCB Repair Logs, Repair Logs Comments Off

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:

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