LC III with no audio whatsoever!

[lopaka1998]

Hi all,

I have an LCIII which was working fine but now has absolutely no audio whatsoever. No squeaks, no interferance or bad ground noises - nothing. I have tried almost everything I can think of - replacing the battery, zapping the parameter ram, checking the power supply's outputs with a DMM (5.10V, 11.84V, -4.9V) - which are close enough to be in working fine. I've removed the 68882 fpu, removed the AsanteLite pds ethernet card, removed the extra 32MB RAM chip and extra video memory chip, swapped the speaker from another (working) LCIII. I've reseated the roms - and even swapped them with the LCIII that I know for sure works - no go.

Please keep in mind that the system works great - with the exception that there is no sound - which makes plying retro games on it somewhat pointless.

As another final irony - I bought this board as a replacement for a LCIII board that I plugged into a bad monitor. The old board's video circuitry is bad. Interesting - a vga monitor (using vga adapter) makes the monitor light turn green - but no output on the screen. That board has perfect audio (POST bong after startup - no problem - and appears to work as much as I can tell minus the video).

So I've got one board (the original) without video (I think the on-board ram chips are fried). I also have my current board which did - but now does not have any sound. Any advise - please! And yes - I've done all the simple stuff like making sure the volume level isn't set to zero.

Advise... Please!

Also if anyone has an LCIII schematic... please let me know.

Best,

--Rob

 

[LCGuy]

I'd say that the caps in the audio circuitry may have given up the ghost, as what seems to be happening to just about all the 68ks now.

 

[lopaka1998]

Thanks for hte info - something to try. The audio capacitors are the ones right before the pds slot hole, right? You wouldn't happen to know the uF ratings and voltages so I could replace them with radial caps?

 

[joshc]

Do NOT replace them with radial caps. Although this might look like the easiest solution, they are nowhere near as reliable as tantalum capacitors. Contact trag on the forums to buy a complete set of replacement capacitors for your logicboard. Search the forum for "surface mount" "remove capacitor" "temperature controlled soldering iron" "leaking capacitor" and you'll find lots of stuff about this very same issue.

 

[lopaka1998]

What about replacing with aluminum surface mount caps? Wouldn't an original 1-1 part be better than a substitute?

--Rob

 

[Osgeld]

One would think, but the tantalum capacitors are in fact electrolytic capacitors, like their can brethren the exhibit the same properties but are made with much more modern techniques, which provide better performance with out mechanical failure (leakage)

the downside is they are more expensive, and when thinking of a electronic device's lifespan 20 or more years is well beyond the image, so the cheaper old type can electrolytic's are used

 

[JRL]

What about replacing with aluminum surface mount caps? Wouldn't an original 1-1 part be better than a substitute?
--Rob

They may work for a short time, but they'll start leaking again and you'll need to replace them again soon enough.

 

[lopaka1998]

One last question - wouldn't Tantalum capacitors normalize the audio to an extent because of their high ESR ratings?

 

[joshc]

One last question - wouldn't Tantalum capacitors normalize the audio to an extent because of their high ESR ratings?

If you had actually used the 'Search' feature of the forum, you would find that dozens of members have recapped their boards with tantalum caps and had no problems at all. Just follow the advice you're given and you'll have a happy working LC again...not hard.

 

[Unknown_K]

Even Tantalum capacitors have a service life just like Aluminum electrolytic. While the aluminum ones might leak with age they generally fail open (no big deal) while tantalums fail closed (short and sometimes a big bang bad for the circuit).

When I recap my boards I use the same type as was on there, if they last another 15 years then I will recap them again if needed (probably not since they wont get the same use). All the ratings are based on temperature when running and hours running.

 

[lopaka1998]

If you had actually used the 'Search' feature of the forum, you would find that dozens of members have recapped their boards with tantalum caps and had no problems at all. Just follow the advice you're given and you'll have a happy working LC again...not hard.

@Joshua Coventry: I will take your reply as meaning that you have not noticed a difference. Your reply seems a little impatient. I never said it was difficult or hard - I repair other devices (tv's, whatever breaks, etc.). To clarify my question, I was curious about the tantalum caps because they generally have a high ESR (effective series resistance) when compared to aluminum capacitors. This would leave me to believe that the output of the audio would be (if slightly) lower than with aluminum capacitors. I was just curious as of what the members have experienced. From your reply I will take it that you have not noticed a change - or at least not one strong enough to notice.

Best,

--Rob