Snow Bros (Bootleg) x2

[Jacmar]

OK so my first ever repair attempt so please be nice Thought this might be a fairly easy fix and so a good one to start with, and I'm sure some of you fixing wizards will be thinking it not worthy of a thread but you gotta start somewhere I guess and this is my start! Apologies if my terminology isn't right at times or I describe things in the wrong way!

Picked this up with a bunch of other cheap faulty bootlegs, with the fault described simply as a coin error...



Board would boot, pass RAM/ROM test but then flash up a coin error with repeating coin up sound. After about 5 seconds of that the board would then reset.

My thinking here is that the board is behaving like it's getting a non stop coin input signal, and I believe all the control inputs on the edge connector should be tied high and when the buttons are pressed the signal is grounded goes low. With this in mind I went about checking the edge connector with my logic probe and sure enough the Coin 1 Input (pin 16) had a permanently low signal. I traced pin 16 of the edge connector to a resistor array and on from there to the adjacent 74LS244 (highlighted below).



I measured the resistance of all the pins on the array and sure enough the one connected to my coin input read only around 1K whereas all the others read 22K. So is it the resistor array or the chip faulty? ... Seeing the chip above had already been replaced I suspected probably the chip ... At this point I thought I'd check the other nearby resistor arrays and found 3 other pins with readings way lower than they should be, I followed these to some other inputs, 1P Up (tied low) 1P Right (floating) & 2P B2 (floating) .. the 2P B2 was connected to the chip that had already been replaced and socketed. So I replaced that LS144 (with one from a donor board) and that fixed that signal which was now tied high and the resistance reading on the array on that pin was now 22K as it should be. This reinforced the theory that the chip was at fault for the coin error and not the resistor so I de-soldered the chip and replaced it - again with one from a donor ... (I didn't have a 20 pin socket (had every other size) but couldn't wait so soldered straight to the board)



Fired up the game .... and it couldn't believe it .... it worked !!!! I was absolutely buzzing



I am still left with a permanently low signal on PIN 18 (1P Up) and a strange really fast toggling mostly high signal on PIN 21 (1P Right) but the game plays fine and I have no issues with moving the character right. I don't think you use UP on this game ?? But I will swap out the LS144 responsible for those signals next and hopefully clear those signals up, then the board should be 100% ! ... I'll update when I've done that...

Much tougher challenges to come no doubt but still well happy with this one

 

[Lurch666]

A fine fix log.
Don't worry about terminology. A lot of this stuff has different names anyway.

 

[Jacmar]

Finally got around to putting this in my cabinet to check all the input controls as I don't have player 2 controls on my test rig. And Player 2 RIGHT was not responding, brought it back to my test bench and still had those 2 pins on the top LS244 held low instead of high.
(I think I was mistaking Player 1 right with player 2 right back at the beginning of this fix).
Anyway swapped it out and now all inputs are working correctly and game plays perfectly.



In the end I had to replace three of the four LS244's near the edge connector to get all inputs working correctly and the game fully playable, but the original coin error fault was attributed to the bad LS244 under RA22.

 

[Georgian2]

Nice and easy repair. A good motivation to dive deeper.

 

[Jacmar]

100% mate, this was just tying up loose ends on my first ever pcb fix
My brain is well and truly fried on more recent ones !!

 

[finfi]

Bueno, mi primer intento de reparación, así que por favor, sean amables. Pensé que sería bastante fácil de arreglar y, por lo tanto, una buena opción para empezar. Seguro que algunos de ustedes, expertos en reparaciones, pensarán que no merece un hilo, pero supongo que por algún sitio hay que empezar, ¡y este es mi comienzo! Disculpen si a veces no uso la terminología correcta o si describo las cosas de forma incorrecta.

Lo recogí junto con un montón de otras copias piratas defectuosas y baratas, con el fallo descrito simplemente como un error de moneda...

View attachment 34102View attachment 34101

La placa arrancaba, pasaba la prueba de RAM/ROM, pero luego mostraba un error de moneda con un sonido repetido de moneda levantada. Tras unos 5 segundos, la placa se reiniciaba.

Creo que la placa se comporta como si recibiera una señal de entrada de monedas ininterrumpida, y creo que todas las entradas de control del conector de borde deberían estar conectadas a nivel alto y, al presionar los botones, la señal a tierra se vuelve baja. Con esto en mente, revisé el conector de borde con mi sonda lógica y, efectivamente, la entrada de Moneda 1 (pin 16) tenía una señal permanentemente baja. Rastreé el pin 16 del conector de borde hasta una matriz de resistencias y, desde allí, hasta el 74LS244 adyacente (resaltado a continuación).

View attachment 34103

Medí la resistencia de todos los pines en la matriz y efectivamente el conectado a mi entrada de monedas leyó solo alrededor de 1K mientras que todos los demás leyeron 22K. Entonces, ¿es la matriz de resistencias o el chip defectuoso? ... Al ver que el chip de arriba ya había sido reemplazado, sospeché que probablemente el chip ... En este punto, pensé en verificar las otras matrices de resistencias cercanas y encontré otros 3 pines con lecturas mucho más bajas de lo que deberían ser, seguí estos a algunas otras entradas, 1P Up (ligado bajo) 1P Right (flotante) y 2P B2 (flotante) .. el 2P B2 estaba conectado al chip que ya había sido reemplazado y enchufado. Entonces reemplacé ese LS144 (con uno de una placa donante) y eso arregló esa señal que ahora estaba ligada alta y la lectura de resistencia en la matriz en ese pin ahora era 22K como debería ser. Esto reforzó la teoría de que el chip era el culpable del error de la moneda y no la resistencia, así que desoldé el chip y lo reemplacé, nuevamente con uno de un donante... (No tenía un zócalo de 20 pines (tenía todos los demás tamaños ) pero no podía esperar, así que soldé directamente a la placa)

View attachment 34104

Abrí el juego... y no lo podía creer... ¡funcionó! Estaba completamente emocionado.:Me parto de risa::Me parto de risa::Me parto de risa::Me parto de risa:

View attachment 34115

Todavía tengo una señal baja permanente en el PIN 18 (1P Arriba) y una señal extrañamente alta que cambia muy rápido en el PIN 21 (1P Derecha), pero el juego funciona bien y no tengo problemas para mover el personaje a la derecha. No creo que uses ARRIBA en este juego, ¿no? Pero cambiaré el LS144 responsable de esas señales y espero que se solucionen. ¡Entonces el tablero debería estar al 100%! ... Actualizaré cuando lo haya hecho...

Sin duda vendrán desafíos mucho más difíciles, pero aún así estoy muy contento con este.

Hi friend. I have a board like yours, but it doesn't work. I only get an orange screen. I'm going crazy trying to get it to work. The simplest thing is supposed to be to flash the ROMs. I don't know which ROMs I have to flash on the four chips above, the ones that go together. Could you tell me which ROM set those four chips have? In MAME, the numbers don't match.
Then, my 68000 CPU only works on pins D0-D7. There, I see activity on the corresponding RAM. D8-D15 is all high. Its corresponding RAM bank is the same. But the RAM is good. It's been checked...could it be the bad CPU?
Thanks. Best regards.

 

[Georgian2]

Hi friend. I have a board like yours, but it doesn't work. I only get an orange screen. I'm going crazy trying to get it to work. The simplest thing is supposed to be to flash the ROMs. I don't know which ROMs I have to flash on the four chips above, the ones that go together. Could you tell me which ROM set those four chips have? In MAME, the numbers don't match.
Then, my 68000 CPU only works on pins D0-D7. There, I see activity on the corresponding RAM. D8-D15 is all high. Its corresponding RAM bank is the same. But the RAM is good. It's been checked...could it be the bad CPU?
Thanks. Best regards.

Any buffers between the ram and cpu on data bus? Ls245?

 

[finfi]

¿Hay algún buffer entre la RAM y la CPU en el bus de datos? ¿LS245?

there are someone.....

 

[Jacmar]

Hey.
My ROMS are not in sockets so I never removed and dumped them. Your issue is unlikely to be with that bank of 4 ROMS at the top of the pcb as they are only graphics roms. have you checked the 2 program roms (under the cpu) with romident?
Also like @Georgian2 says check the LS245 above the cpu, one will probably handle the D8-15 signals. seems a more likely cause

 

[finfi]

Hey.
My ROMS are not in sockets so I never removed and dumped them. Your issue is unlikely to be with that bank of 4 ROMS at the top of the pcb as they are only graphics roms. have you checked the 2 program roms (under the cpu) with romident?
Also like @Georgian2 says check the LS245 above the cpu, one will probably handle the D8-15 signals. seems a more likely cause

Hey.
My ROMS are not in sockets so I never removed and dumped them. Your issue is unlikely to be with that bank of 4 ROMS at the top of the pcb as they are only graphics roms. have you checked the 2 program roms (under the cpu) with romident?
Also like @Georgian2 says check the LS245 above the cpu, one will probably handle the D8-15 signals. seems a more likely cause

I've checked the two software ROMs, and according to ROMIdent, they're fine. I've checked the 245s, and they seem fine. I've done a pick-up with new chips, and nothing changes. The signals are a little low, though. There are a lot of floating points. Will I have to desolder them?

 

[finfi]

Those four ROMs fell out of order and got all mixed up. I tried to flash them again, but I don't know what the .bin file is, and ROMIdent can't identify them.The other 3 roms, program and sound, are correctly identified by romident.

 

[Lurch666]

Is the CPU getting a proper reset?

 

[finfi]

Is the CPU getting a proper reset?

Well, I honestly don't think so. When I turn on the board, the reset signal isn't correct at all. It doesn't perform a clean upload. But while it's on high, I reset it by grounding it, and it still doesn't respond. The screen remains orange.

 

[Jacmar]

Another one of these bootlegs fell into my hands very recently and whilst I had the 2 recent original fixes still fresh in my mind I decided to go straight into this one ....
BOARD 2



Not in the best of condition and clearly seen some previous work, CPU looks to have been replaced, some of the RAM socketed, a number of TTL chips replaced and a few trace repairs - the most obvious one being the white jumper wire on the solder side ... Looks like whoever did the work just smeared the whole solder side with flux and then used their spare dynamite to get the chips off But must've been all out of IPA though to clean up afterwards! Lovely and sticky !!
No shorts though so fired up to see what the state of play was ....



So good news, game was running and sound working as it should ! So just graphics issues to sort out ....
Started off with a close visual inspection of the board and came across a number of problems with traces ....



The missing signals had been bodged on the parts side with bits of wire but these traces (particularly the left one) could've been shorting on other pins causing all sorts of issues. Little tidy up job on these done and checked a number of other trace repairs done by someone previous which were all generally ok, if not great looking. The white piece of jumper wire on the solder side was also loose and flapping around so repaired that with a tiny piece of wire through the via as the break was only a small one between the via pad on the solder side and the trace. So with all the trace issues I could see either checked or repaired I fired it up again ...



Progress ....
Suspecting address issues I scoped the RAMs and ROMs and signals all looked healthy. Not desperate to start mapping the logic to specific areas of the board, I first went back and had another really close visual check in case I'd missed anything. I'd concentrated on the traces before but switched to looking at IC's and after a little while spotted a dodgy looking leg (pin 13) on a LS157 (IC306) in the top corner near the Jamma connector. On close inspection it was apparent that the leg wasn't going through the board, confirmed by looking underneath- no pin sticking up out of the board. Must be folded underneath the chip and it was. Pin was definitely not making contact with the pad as the scope showed it floating....



Removed, cleaned the area and replacement socketed in ....This cleared up the remaining graphics issues ...



Removed some redundant labels, put about 10 decoupling caps around the board as there were none, and this ones looking good !

 

[Judder]

I love reading these fix reports - amazing the detail it takes to fix the boards and fantastic writeups 👍