May 292020
 

Philmur has sent me his Pacman diagnostic ROM.

Pacman test ROM – philmurr 05/20

Fits at location 6E

Tests programme, colour, video and sprite RAM 1 (note sprite RAM 2 is write-only)
Displays sprites dropping from screen to show sprite select and addressing is working (tries to show all 8 but most boards only have 6)
Shows real-time status of inputs and DIPs

Colour RAM – 4P, 4L
Prog RAM – 4R, 4M
Video RAM – 4N, 4K

Sprite RAM 1 – part of 4R,4M but may make it clearer to people when testing

File can be downloaded in the “Downloads/ROM files/Diagnostic” menu

Thanks to Philmur for his hard work and for sharing this

 Posted by at 4:32 pm

Metro Cross repair log ( same hardware of Baraduke)

 General, PCB Repair Logs  Comments Off on Metro Cross repair log ( same hardware of Baraduke)
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 BaradukeĀ  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 šŸ˜‰

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 on Pacland repair log #5
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@7KĀ  was stuck low thus selecting the wrong sprites on the sprites eproms

After changing it board was fixed:

Mar 262020
 

I recently got two Operation Wolf boards from Muddymusic to fix.
This board was not booting at all and I got a screen full of flickering garbage

I removed all four of the 27C512 program EPROM’s and verified they were good. All of them matched the “World, Set 1” version in MAME.

I confirmed continuity between all the address, data and control pins of both EPROM’s and RAM was present and correct and it was so I opted to remove the two TMM2063 work RAM chips and test those

As you can see both failed. I replaced them and tested but there was no change.
Next I started looking at the reset circuit.

Here is the main reset circuit taken from the schematics

Using the logic probe I found that signal “/TMCL” (timer clear) was floating. Shifting focus to grid A5 on the schematics we see that this signal comes from pin 13 on the 74LS138 at location IC60.

Further probing found that the A18 signal on pin 2 was also dead. This signal is the buffered MA18 (address bus pin 18) and comes from the 74LS244 at location 65. Checking the signal on the LS244 revealed that it was present so there was a break in the trace some where.
I couldn’t see anything obvious so I patched it with some Kynar wire

No on boot up I get no more resetting buyt the screen is full of garbage still

Next I started looking at the custom PC080 tilemap generators, more specifically the RAM connected to it

Checking both of these with the probe showed me there was no activity on most of these pins and some others were stuck high

I removed both of them and checked them, obviously both failed

Replacing both of these now gives me something to see.
In test mode I get this

I looked into this fault for a good hour or so before I decided the RAM I fitted was too slow. Swapping for a faster RAM type fixed both of these issues.

Now the board would successfully pass the self test in the test mode I could see that I had an issue with colours.

I started off probing the colour RAM at locations IC64 & IC65 and quickly found bit 4 of the address pins stuck low

Using the schematics I could easily trace this back to a 74LS157 at IC52

Replacing this gave me my colours back

Now onto the sound board.
The good news is all the music was present and correct. The bad new was all the voice samples were not.

Again, using the schematics I see that ultimately the addressing for the Maskrom at IC21 gets set by a bunch of 4-bit counters at IC27-IC30.
Probing these I found that the UP counter wasn’t pulsing at all

Checking the 74LS04 at IC32 revealed this inverter was bad so I replaced it and sound was restored but the sounds just carried on playing one after the other (never got a video of this).
The Z80 sets the start and stop data by writing values to address $C002 & $C003 respectively which gets latched by a couple of 74ALS574’s and fed into the B side of a 74LS688 comparator

Using the MAME debugger I could see that the data being written to the 74LS574’s was correct but probing the /A=B output pin 19 of the comparators showed that these were either never matching or they weren’t working.
I couldnt find issues up stream of these so I desoldered them and replaced them with pulls from another board as I don’t have any spares.

I now have working sounds and fully working board set ready to return.

 Posted by at 1:43 pm
Mar 262020
 

I had this Fever SOS (international version of Dangun Feveron) PCB since many Years. Here is a picture of the board with the two chips I had to replace highlighted in red:

It had flickering sprites (the problem being pretty hard to photograph, I’m not able to show screenshots of it). In other terms, every second frame of sprites was not displaying.

1) The sprites are generated by a large 240pin custom chip labeled 9838EX002 – 013 on this board. Closer inspection revealed a cross marked on it by a previous repairer as well as a mark on pin #226. That pin goes to the RAS (Row Address Strobe) pin (#14) of a DRAM (424260) at U36, which is one of the two DRAMs that deals with sprites, each of them displaying alternatively one frame after the other.

There was no signal at all on that pin (#14). Probing the equivalent pin on the adjacent DRAM at U35 showed a pulsing signal. RAS being a signal going towards the DRAM meant that the large custom chip wasn’t giving the signal needed at pin #226.

I needed to change that large custom chip. These being on Cave 68000 systems, they are unfortunately available mainly on rare and expensive games (list available in the Cave 68000 MAME driver). After a long time, I finally had the opportunity to grab a UO Poko board which has the same chip, even labeled not exactly similar: 9749EX004 – 013.

Left is the faulty chip taken off the Fever SOS board. Right is a working chip taken off a UO Poko board. Notice how the left one blistered after heating it for desoldering, while the right one didn’t change.

2) Unfortunately, swapping the chip did not resolved my sprite flickering issue but at least the signal at pin #226 was then looking good. Probing the linked DRAM at U36 showed some weird looking signals on a few I/O pins (#2, 3, 4 & 5 pins).

I swapped it with a functioning DRAM (a NEC 424260). That finally resolved the flickering sprites problem.

Board fixed !

 Posted by at 9:35 am