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CPS2 sound issues

Apocalypse said:
Yes.
From my notes, with garbled sound issues I replaced a lot of the LS374s @2N, 2P, 2R, etc. All TI branded.
Click to expand...

Ok, time has passed fast again. Meanwhile I got my logic probe digged up, watched couple of videos just a reminder of it's use. Collected all the chips as a list and nassekova collected me the pinouts to a single PDF easier to watch when poking with the probe tip.

Now I finally prepared to make measurements. But another problem arised what I really didn't think earlier (I should have!). If I don't have A and B boards together the CPS2 A board plays pretty much dead. Powers up, but nothing happens (except white picture on screen)... If I put the boards together I can't use the probe as the chips are under the B board...

How did you figure out the faulty chip?
 
stt1 said:
Ok, time has passed fast again. Meanwhile I got my logic probe digged up, watched couple of videos just a reminder of it's use. Collected all the chips as a list and nassekova collected me the pinouts to a single PDF easier to watch when poking with the probe tip.

Now I finally prepared to make measurements. But another problem arised what I really didn't think earlier (I should have!). If I don't have A and B boards together the CPS2 A board plays pretty much dead. Powers up, but nothing happens (except white picture on screen)... If I put the boards together I can't use the probe as the chips are under the B board...

How did you figure out the faulty chip?
Click to expand...
This may look odd, but you can check for a lot of issues on the bare, unconnected, A board. There's lots of pull ups to get the TTL chips in a known logic state. You can check for shorts (pins pulled low when they shouldn't be) and invalid logic states. You can't be 100% sure something is good or bad, but major faults will be easy to spot.
With the boards connected you can check the connectors' pins and cross reference them with chips on both boards. Vias can also be handy for this.
 
@stt1 I took a B board with the same symptom as yours and fixed it by changing the 2NLS374.
 

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Thanks for the tip. I decided to go on crash course with this one and just plainly swap those 2N, etc. TI chips and see when all is good. Now, checking for chips, there are plenty of variants available (and not that lot just plain "74LS374"). Does someone know right away a list of known good variants to buy as replacement? Would for example SN74LS374DW be good to go?

Yes, I know, by digging through the data sheets, I can find the difference between the versions and compatible or not, but that's another rabbit hole in the time space...
 
stt1 said:
Thanks for the tip. I decided to go on crash course with this one and just plainly swap those 2N, etc. TI chips and see when all is good. Now, checking for chips, there are plenty of variants available (and not that lot just plain "74LS374"). Does someone know right away a list of known good variants to buy as replacement? Would for example SN74LS374DW be good to go?

Yes, I know, by digging through the data sheets, I can find the difference between the versions and compatible or not, but that's another rabbit hole in the time space...
Click to expand...
Just ignore the bit before and after the 74LS374.
The prefix usually identifies the manufacturer (SN = Texas Instruments) and the suffix the package type or other specific stuff (lead free, etc).
You can choose the same part from other manufacturer, they are all compatible.
Just make sure it's 74*LS*374 and not, say, 74*HC*374. Compatibility is not guaranteed in that case.
Also check the actual dimensions of the part. Some are wider than others. You will have to check the datasheet for that.
The 'DW' suffix in the SN74LS374DW is used for that, but that is on TI parts -- others may use a different system.
 
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Yes, I know that HC should be avoided. However, isn't the latter part really not that important?

For example (Mouser catalog):

SN74LS374DW - Flip-Flops Octal

SN74LS374NSR - Flip-Flops Octal D-Ty Edge Trig F-F W/3-State Otpt

SN74LS374NSRG4 - Flip-Flops Octal D Type Edge Trigred FlipFlop

(all Texas Instruments, btw)

This sounds pretty different... But in functional sense they are after all just the same?

Physical size, ah yes, that makes indeed some sense. Need to measure first the originals... I'll try to remember doing that tonight. Maybe during weekend night I have then time for checking the datasheets... :)
 
stt1 said:
Yes, I know that HC should be avoided. However, isn't the latter part really not that important?

For example (Mouser catalog):

SN74LS374DW - Flip-Flops Octal

SN74LS374NSR - Flip-Flops Octal D-Ty Edge Trig F-F W/3-State Otpt

SN74LS374NSRG4 - Flip-Flops Octal D Type Edge Trigred FlipFlop

(all Texas Instruments, btw)

This sounds pretty different... But in functional sense they are after all just the same?

Physical size, ah yes, that makes indeed some sense. Need to measure first the originals... I'll try to remember doing that tonight. Maybe during weekend night I have then time for checking the datasheets... :)
Click to expand...
They are all functionally the same. The 74xx family is standardized. The last three digits define what the IC does.
The middle (LS, HC, AL, F,...) defines -- in broad terms -- speed, power consumption and voltage levels for high and low.
 
Thanks. Sometimes the letters after digits seems to be very important and sometimes not... For example M6809 and M6809E are not really same thing, there is significant difference already in the pinout level.

Does not really make easy to understand things...
 
You'll get the hang of it with time. RAM chips have really weird and inconsistent markings between manufacturers, NEC parts seem to be completely made up (uPD7800C is a Z80), and 74xx ICs have some quirks... When in doubt I check *what* the part is and then find equivalents.
You'll get there with practice, trust me :)
 
Finally I got replacement parts to my desk (arrived actually about 1,5 weeks ago) - hardest task was to get the order big enough for avoiding ridiculous shipping costs. Ordering of parts didn't really work out super smoothly: the letters after digits were apparently NOT that unimportant - 74LS374 I have now are much wider than the originals. Anyway, fortunately the pads in CPS2 PCB are wide enough that I can use 374s without problems. Need to be much more careful with that latter part as well in future.

Last week I removed the suggested location 2N, cleaned the area under the chip and old solder from pads. Noted several traces going through the PCB under the chip. As I had limited time available, I didn't want to rush and stopped there.

Yesterday evening I measured continuity for each trace going through PCB, from pad to actual contact in the connector. All were good, so I soldered the new 374 in place and measured that no legs are shorted. Testing the PCB revealed that some of the sharp noises in sounds were gone, but sounds were still heavily distorted and wrong, not "musical" at all. As I still had some time left I decided to swap the next chip, in place 2P. Repeated the procedures, including short-test... Now the sounds were again another step better, they are partly more musical, spoken parts are much cleaner... But still not yet there.

Maybe the next chip does it!
 
Several toasted... The sounds got better with both I have swapped so far. At least one more to go.
 
Houston, we had a cap leak towards 2R...

2R_Cap_leak.jpg
 
stt1 dropped the board to me as I have lot of experience fixing boards in bad shape.

Tinned copper sheet from one side,sliced it.

IMG_7279.jpeg


Cut slices to pads and glued them with epoxy (jb weld handles 300C once cured), tape over to hold them. I used hot plate set to 85C to cure the epoxy in 2 hours
IMG_7280.jpeg


Soldered new chip and fixed some traces. Added protective lack. All pads were in bit bad shape but solder stuck after using fiberglass pen and cleaning them
IMG_7286.jpeg


Didn't fully fix sound so quickly removed rest of the 74ls374s (takes like 2 minutes with 400C hot air)
IMG_7287.jpeg


Here you can see bit of my repair setup :)
työntouhu.jpg


All new chips and sound works!!!
IMG_7288.jpeg
 
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Awesome! Thank you Miikka, I think me and @stt1 started this "CPS2 multi" project in 2019 or so, and it has been a bumpy ride... :cursing:

First we got 2 broken B boards, then battery acid destroyed A boards, and finally when we thought that now we have a working units, these sound issues came up...

So FINALLY we (should) have 2 working sets, kudos (for both of you)!
 
Yeah, and I didn't have suitable glue (heat resistant enough) for holding the replacement traces in place when soldering the new chip. Another good reason to ask help from someone who already has the equipment ;)

Thanks miisalo. And in top of fixing the PCB we had a good 2 hour chat last night... Really haven't seen so much since COVID started...

This week I'll install key writing cables to both PCBs and try out all the games in multi.
 
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