Repair Logs – Page 42 – JAMMArcade.net

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!

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:

Irem M92 double repair log #2

PCB Repair Logs, Repair Logs 6 Responses »

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

Megazone repair log #2

PCB Repair Logs, Repair Logs Comments Off

Aug 102017

Got this faulty pcb for my collection

Game was resetting over and over right after the first stating screen without even the possibility to see the diagnostic screen “RAM ROM OK”

The code was running and the watchdog was triggered by some event which I eventually found in a faulty 2114 SRAM @E15 on the video board

Marked in red on the actual pcb:

After changing it, the boot process went on until it displayed RAM and ROM OK but it reset again just before screen with the white grid.

At this time I was complete blind , missing any programming skills I couldn’t check what the code missed to go on.

I had a suspect on the sound part and after checking the clocks on the 8039 MCU I noticed it was completely missing.

The oscillator was working correctly and from the schematics I could see that the clock for the 8039 and the AY is generated using some 4bit binary counters 74ls293, very difficult to find on other boards.

Probing pin 9 of 74ls293@A12 it was stuck high while on pin 10 I had the clock.

I proceeded to test it out of circuit but was tested good.

Not sure about the reliability of the tester, I found a Starforce boot which use one 74ls293 and I installed it in a socket on megazone.

Still reset and no clock from pin 9

The output of the IC@A12 goes to pin 8 of a 74ls240, therefore I decided to test pin 8 of IC @D14 against +5V and it gave me a short.

After changing it the game finally booted without any other faults

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