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Sound Board A-12738-50020 WH20


stuba

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I have a couple of interesting problems and they may be related, fairly new to this so would appreciate someone double checking my approach - Someone also may have encountered something similar and maybe can point me straight to problem.

 

2 problems on powerup.

 

1. Factory reset every time. Batteries are fine. Battery holder is fine and correct voltage on CPU board (4.8). Following Marvins guide I have tracked problem to D2 which is testing 4.8 one end and 2.2 other end - should only be a .5v drop so conclude replace D2.

 

2. The main problem. I get 5 beeps on powerup (U14 error). I then get 2 U14 checksum errors (Sound board and bigfoot). The board did not have a U14 eprom when i got it - there were no sound effects, voices. From what i can gather U14 has the voices, sound effects. I replaced the U14 - same errors.. BUT sound testing now has all the voices sound effects except the 100M(?) which is a staticcy noise. Also note the sound board has cooked LM1875 which has been replaced (prior to me) and is obviously working (but job is a bit rough), looks like C15 replaced at same time.

 

Concerns/Issues/Questions:

Can the CPU board problem be affecting the sound board?

The U14 i put in was good and as proof it's working but why i am getting the 5 beeps error if its good, can a ROM partly be bad, one sound effect is missing?or could this be in the SB itself? maybe a U14 trace/component broken or dry?

 

I can swap a TZ board in to check the ROMS but don't want to do this until the CPU board problem fixed. Don't want to screw up my TZ board as well.:redface

 

Approach From Here:

Fix the D2 CPU problem. See if this makes any diff to SB. Test the ROMS in the TZ board - swap the TZ board into the wH20 and see if the ROMS ok. This will isolate prob to SB or ROMS. One other question while I'm going - sound quality is not great - is it worth just replacing all the caps on the sound board anyway? does anyone do this as a matter of course? Overkill?

 

Any thoughts, comments appreciated. I want to be sure I'm barking up the right tree.:unsure

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Hi Stuba,

Not familiar with this board but is D2 a standard diode and not a zener? My multimeter has a diode tester on it and can measure the 0.5-0.6 voltage drop across the diode with the power off to the board. D2 may be faulty but if you meter can do this it might confirm the diode is faulty. Its possible the Rom could be corrupt. If you have a eprom burner you could read the rom back and check its checksum against the rom image.

 

Regards Derek

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Hi Stuba,

Not familiar with this board but is D2 a standard diode and not a zener? My multimeter has a diode tester on it and can measure the 0.5-0.6 voltage drop across the diode with the power off to the board. D2 may be faulty but if you meter can do this it might confirm the diode is faulty. Its possible the Rom could be corrupt. If you have a eprom burner you could read the rom back and check its checksum against the rom image.

 

Regards Derek

 

Thanks Derek. It's not a zener. It's a 1N4148. 5c at Jaycar. The plot thickens tho - i removed D2 and it was bad, it fell apart when i de-soldered it - the ultimate semi-conductor:badgrin, replaced it and this fixed the factory settings restored/reset problem. Stage 1 complete. The new one passed .5v drop test so all good on CPU board. note - can be measured with board power off because power source is the 3 x 1.5 v batts.

 

I then put the sound board back in and the U14 checksum error has dissapeared - :lol but I'm now getting a u15 checksum error:x! 5 beeps has become 4. Given up for today but will get u15 and u18 roms replaced as well. Sound test is failing on 2 sound effects (bigfoot scream and 100M) - which was the same as yesterday.

 

The power prob on CPU board was definitely messing with the Sound Board in some way. Starting to be fairly certain it is a rom problem though. I think those missing sounds have to equate to a checksum error. The other interesting news is that the sound quality has dramatically improved (on the sounds and music that work:))

 

I don't have rom burner but ordered one today from darkwire (willem) hopefully will help. will update after i try new roms...

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It's not at all uncommon to have Game & sound rom shit themselves.

 

I've had U15 checksum error on my WH20 after I installed a new set of roms. Put the old one back in and away she went.

You might get away with removing the chip and reseating it. Make sure you observe good anti-static behaviour. The sockets Williams use are not the greatest.

 

I'm thinking of being a total anal retard and replacing all the Williams IC sockets with good quality gold plated ones. They don't cost much.

I have them on all the LM339 chips.

 

The sound boards are very reliable as a whole. Thats why no-one makes an aftermarket board.

 

I have had a problem with LM 1875 Audio amp on one board.

They run soo fucking hot I'm surprised they don't blow up more often.

Cheap and easy to find chip.

 

Very rarely the electronic pot chip chucks in the towel. E9503 these are also readily available & much cheaper than the chip on the later model board.

 

Time will cause this and other boards to fail by virtue of the Electrolytic Capacitors. Good idea to change them all if you have the time and money.

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Good work with the diode. I guess when it fell apart it was a bit of a give a way!

Its interesting the the sound quality has improved.

 

I was thinking that the rom was faulty but now that the problem has shifted to U15 it may indicate different problem. What you mentioned about a broken trace on the board might be right. At least once you have the willem you can definitely confirm the roms. Only simple things but have you checked none of the roms have bent legs underneath. Marvins guide suggest the cables can sometimes be a problem. If you have another board you might be able to swap the ribbon cables over.

 

All the best with the troubleshooting.

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It's not at all uncommon to have Game & sound rom shit themselves.

 

I've had U15 checksum error on my WH20 after I installed a new set of roms. Put the old one back in and away she went.

You might get away with removing the chip and reseating it. Make sure you observe good anti-static behaviour. The sockets Williams use are not the greatest.

 

I'tt try a reseat later today, good idea. Derek - I can check no bent pins at the same time.

 

The sound boards are very reliable as a whole. Thats why no-one makes an aftermarket board.

 

I wondered about that. I did see if any were available but then decided i had better fix this one in the absence of them.

 

Time will cause this and other boards to fail by virtue of the Electrolytic Capacitors. Good idea to change them all if you have the time and money.

 

I'll look at doing this after I have sorted probs. Caps at jaycar are cheap and i have already ordered some of them but I have not been able to source 4700uF 35v and another one as well .01M (never seen this description before)??

 

I'm 95% sure a good set of roms will get it over the line "no fault" wise, i'll update after I test that...

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