Tales from the Crypt
Data East, 1993I'm not getting any sound on my TFTC. The sound eproms work. I tested them with another board. My voltages are good coming in to the board and I'm getting -5 at C49. Is there some way to test the PAL chips without just replacing them with new ones?
Check your 5Va it also has a unique regulator from the +12V board input. It can be checked at U26 pin 5. I wouldn't mess with the PAL chips.
I would first check your volume control pot. It is a common failure point in sound problems.
Since you get absolutely no sounds from the board, the first board common element to all three channels is U26 TDA1543.
amplifier on the sound board is a good guess. Do you get ANY sound? Even if it is just a hum? Also give electroyltic caps a good visual inspection, pay close attention to ones near heat sources for bulging, split wrappers, leaking.
Quoted from GoodToBeDad:Thanks for the reply.
I'm getting 5V at pin 5 on U26. I also swapped the sound board from my LAH in to TFTC and it worked fine. So I know the potentiometer is working. Anything else you can think of?
It does not sound like you have properly ruled out u26 but are ignoring that and asking for other suggestions 
Quoted from barakandl:amplifier on the sound board is a good guess. Do you get ANY sound? Even if it is just a hum? Also give electroyltic caps a good visual inspection, pay close attention to ones near heat sources for bulging, split wrappers, leaking.
The board had three amps. If one died, you'd get sound from the other two. Therefore I rule out amps.
Quoted from markmon:It does not sound like you have properly ruled out u26 but are ignoring that and asking for other suggestions
I"m not ruling anything out. I checked and got 5v and am asking for other ideas. What else can I do to check U26?
At U26 pin 3 - digital data in , pin 1 digital clock Use your logic probe to verify you are getting clock and data in.
pin 6 is Analog Out Left channel (need a scope to check)
pin 8 is Analog Out Right channel (need a scope to check)
If you have a signal generator, you could insert 1khz signal at pin 6 and at pin 8 to confirm
all of the amplifier sections are functioning correctly.
I don't know if this will work, but if you take a set of earbuds, and listen to the outputs of
the U30 dual op amp. Pins 1,7 and board ground. There may be enough analog signal
to drive the earbuds.
Since you hear no sound, it is unlikely all three power amps are out. That's why I would
start at the beginning of the amplifier chain at U26 to verify you are getting digital signal
in.
Sound board problems are difficult to sort out.
I don't see how a DMM can provide you any information for this problem beyond measuring the specific voltages which you already have accomplished.
Even a logic probe is not appropriate but will provide limited information.
I this point since you cannot confirm the operation of U26 you might want to consider sending out the board for repair. You might try the earbug technique to see if you can hear any sounds after the dual op amp. You will
have to locate the common/ground for the left and right buds, and then hook up the left and right to the outputs of the op amp.
Quoted from minnesota13:I don't see how a DMM can provide you any information for this problem beyond measuring the specific voltages which you already have accomplished.
Even a logic probe is not appropriate but will provide limited information.
I this point since you cannot confirm the operation of U26 you might want to consider sending out the board for repair. You might try the earbug technique to see if you can hear any sounds after the dual op amp. You willhave to locate the common/ground for the left and right buds, and then hook up the left and right to the outputs of the op amp.
You can kind of use a DMM at a logic probe. in a 5v ciruict, 0v is low, 5v is high, between (2.5v) you can assume it is pulsing. Advanced DMM might be able to check frequency of a pulse too which is clue in some circuits.
Quoted from minnesota13:At U26 pin 3 - digital data in , pin 1 digital clock Use your logic probe to verify you are getting clock and data in.
My logic probe came in and here's what I'm getting on U26.
On my probe I have a high LED and a low LED.
pin 1: High Low
pin 2: High
pin 3: Low
pin 4: Low
pin 5: High
pin 6: Nothing
pin 7: Nothing
pin 8: Nothing
This is different from my working sound board which gives me both a High and Low LED on pin 2.
Does this tell you anything?
This probe is also a pulser. I am getting a tone through the speakers when I touch the correct chips.
Thanks again for your help.
On U26 it looks like you are not getting data in and therefore nothing out. Clock appears to be coming in.
Problem looks to be further upstream.
I did some more poking around with my logic probe and comparing readings with my working LAH and looking at the schematic. U9 (bsmt2000) is fine. I swapped it out with my LAH and there was no change in any readings. The problem appears to be somewhere between U9 and u26. U9 and U23 both feed in to U25 which feeds in to U26. U23 is giving me some funny readings and I'm not getting any high or low LED on 8 of its 16 pins. I suspect this may be where the problem is. Does this sound reasonable?
Wanna join the discussion? Please sign in to reply to this topic.
Great to see you're enjoying Pinside! Did you know Pinside is able to run without any 3rd-party banners or ads, thanks to the support from our visitors? Please consider a donation to Pinside and get anext to your username to show for it! Or better yet, subscribe to Pinside+!
This page was printed from https://pinside.com/pinball/forum/topic/possible-to-test-u19-and-u20 and we tried optimising it for printing. Some page elements may have been deliberately hidden.
Scan the QR code on the left to jump to the URL this document was printed from.
Prairie Village, KS