PCB Repair Logs – Page 5

Operation Wolf repair log #4

Apr 112020

Another Operation Wolf repair!
This one belongs to Frothmeister on UKVAC.

Again, we have a nice little fault label

So to start with there was no sound. I did a couple of signal checks to see if commands were being written to various IC’s but saw none of them so I just removed the RAM which of course failed.

Fitting a new RAM brought the sounds back but the samples were garbage

Samples are all stored in the 40 pin MASKROM.

I attempted to read the MASKROM as a 27C400 EPROM in my programmer but it gave me errors

As I had a scrap sound board here I swapped this ROM out and retested.
Samples were now restored but I had the same issue as in a previous repair where the sounds started playing and never stopped.

Time to check out the comparators.
I quickly found the comparator with a stuck output at location IC18

Replacing this fixed my faulty sample playback for this one but I found another by playing sample 2E.
Using the same technique I found another dead 688 at IC39.

To determine which channel the game uses for various samples I use the wonderful MAME debugger.
If you look at the memory map for the sound CPU in the MAME source you can see the addresses that get written to to set the START and STOP values.

Address ranges $B000 – $B006, $C000 – $C006, $D000 – $D006 & $E000 – $E006 are what we are concerned with so set some breakpoints in the debugger and fire up the Operation Wolf test menu (dont forget to set the debugger focus onto the sound CPU).
Play the sounds that cause issues and see which address gets written to.

Now look at the schematics

From here we need to work out with signal is address $C000.
A15 & A14 give us an address of $C000. the 74LS138 at location IC14 gives us the enable line for the channel. A15 enables the 138 itself and A14 selects the relevant output, in this case its input C which enables (active LOW) pin 11. This in turn enables IC54 which as you can see from the signal names is channel B.
Following the schematics further we find the 74LS688 comparators responsible for this

Probing the only output on those comparators (pin 19) and playing the sample shows me which one isn’t toggling. In this case it was IC39.

All fixed

Operation Wolf repair log #3

Apr 102020

Another few Operation Wolf boards in at the moment. This one is from Unit504.

There is a nice little tag on this telling me the faults which really helps me keep all these boards together and where to start looking.

First job was to look into the gun shot register issue.
I did a quick test and could see the screen flash when the trigger was pulled so I knew that wasnt the fault
Following the circuit I come to the 74F74 IC which is used to latch the gun co-ordinates.

I normally wouldn’t start looking at this part but it was already socketed so decided to pull the chip and test it. It failed an out of circuit test.

I replaced this with a 74ALS74 and it seems to be be fine.
Now all the gun shots register as expected.

Next onto the sound.
None of the sounds were working at all and I didnt believe that all the seperate circuits for making sounds would be dead so looked a bit closer at the CPU side of things.
First off I checked the ROM and it dumped out fine.
Next the RAM. An inspection of the RAM showed signs of corrosion

I removed and tested it and thankfully it failed

Looks like that corroded pin has broken contact somewhere. Anyway, replacing the RAM brought all the sound back to life and completed this repair.

Metro Cross repair log ( same hardware of Baraduke)

General, PCB Repair Logs Comments Off

Mar 302020

The game at first didn’t boot due to the watchdog circuit being triggered.

There were 4 work srams by Toshiba and first one from left was faulty.

Unfortunately soon after , game started to reset again and the second sram from left failed.

The PCB had then all sprites in a single row and was missing the text on the upper and bottom area and soon after it losts also the BLUE component

Decided to start from the easy part and restored the missing colour.

Green and blue components are generated by the PROM @ 1N.

Signals were good so the fault was in the 74LS173@2P which had all output stuck at 0V

After changing the TTL I restored the blue component.

The missing text was due to the 74LS195@6L , while checking it I saw that the text reappeared but glitched

After changing it I finally had again the text

To restore the sprites I decided to concentrate on the \HSET signal on the sprite address generator circuit.

This signal comes from pin 22 of CUS35 and it was always stuck LOW. I took another CUS35 from a Baraduke board and the problem remained.

So I decided to look at the other side and checked two 74LS173@9N and 9P

I shorted for a brief moment the \Hset signal to 5V and the sprites were correctly drawn again and the signal was oscillating.

But I noticed that some sprites has some glitching on colours.

I decided to replace both of them

Board was 100% fixed

Of particular note is that all the faulty TTLs were by Texas Instruments ( not Fujitsu!) and of uncommon type.

It seems Namco had a stock of these ICs to be used on an hardware design 😉

Please note also that CUS35 is 100% compatible with CUS48 from later Namco system 1 games.

Pacland repair log #5

General, PCB Repair Logs Comments Off

Mar 292020

Second Pacland pcb I got for repair is a Namco one.

It had some sprites wrongly selected by the game code

After checking on the schematics the sprite addressing I found this:

pin 16 of 74ls377@7K was stuck low thus selecting the wrong sprites on the sprites eproms

After changing it board was fixed:

Pacland repair log #4

PCB Repair Logs Comments Off

Mar 292020

Got two Pacland pcbs to be repaired from a friend.

Fist one is a Sidam Pacland which showed the following problem:

All the screen had shadowed colours going up and down vertically.

By expecience whith similar problems on different hardware I understood it was a Hblank problem.

The game didn’t shut off the screen at the borders so the monitor didn’t have anymore the black reference.

Looking at the schematics I found immediately a clear reference to the blanking circuit:

Compblank was oscillating, while COMPBLANK A and \COMPBLANK A were stuck.

Chaning the 74LS74@6M fixed completely the issue

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