| Click here to select a new forum. |
| Recapped 840av with intermittent sound |
Posted by: d3jsp on 2025-08-27 23:52:05
Have a 840av that is already recapped with red polymer caps. Sound from the headphones jack work just fine but onboard speaker is intermittent. Sometimes it works and is loud, but most of the times it's extremely faint or nothing at all.
I would assume this is a bad c48 from bomarc's schematic's right? But it just seems so unlikely that a polymer cap is already going bad.
Anyone have similar experiences with the 840av and can this be anything else on the board? |
Posted by: croissantking on 2025-08-28 01:06:03
It might be dirty contacts inside the headphone jack. When you remove the headphones, it closes a contact that routes the audio to the onboard speaker, and these often get dirty or corroded with age. Then you get issues like you’re having.
- try spraying contact cleaner into the jack
- try inserting and removing a headphone connector multiple times |
Posted by: cheesestraws on 2025-08-28 01:15:45
Yes, likely to be the contacts in the jack. But check the whole signal path always, don't just blindly assume it's capacitors, there are plenty of other things to go wrong in those machines. |
Posted by: croissantking on 2025-08-28 01:50:12
Yes, likely to be the contacts in the jack. But check the whole signal path always, don't just blindly assume it's capacitors, there are plenty of other things to go wrong in those machines.
Yes - it’s exceedingly unlikely to be a brand new capacitor that’s causing the issue unless they installed it backwards 😛
I’m working on an 840AV board right now that has no video and no sound (except for the startup chime). The original caps ravage these boards so it’s generally corroded traces that are the issue. |
Posted by: cheesestraws on 2025-08-28 01:57:03
Yes - it’s exceedingly unlikely to be a brand new capacitor that’s causing the issue unless they installed it backwards 😛
Given those symptoms, though, might also be a dodgy solder joint on one of those new capacitors... being fully open or high resistance much of the time but then either warming up or physically flexing to make contact sometimes. |
Posted by: d3jsp on 2025-08-28 13:51:08
The headphone jack itself is fine. Traces around speaker looks fine too. My guess is that it could be the TDA7052A amplifier chip? Since it doesn't seem like headphone sound goes through this |
Posted by: d3jsp on 2025-09-07 22:56:28
Swapped for another DA7052A from aliexpress but still no sound. The new chip is getting extremely hot even though the input measurements look correct from specsheets
pin1 VCC ~8V
pin 4 mute is ~0.9V. This goes to pin 40 on the 2300 instead of 37 like what is in bombarc's schematics, strange!
pin 5 and 8 goes to speaker. Gives around 5-6V all the time, not sure if this is right
pin 3 and 6 are ground
pin 2 signal seems correct |
Posted by: d3jsp on 2025-09-07 23:11:20
with the original chip, I am getting
pin1 VCC at ~ 12V
and pin 4 at 5v
and pin 5 and 8 at ~5.8V
Even though it doesn't work and there is no sound, the chip does not get hot at all. This leads me to suspect if these chips have different specs or did I get fake Chinese chips? |
Posted by: d3jsp on 2025-09-07 23:51:24
Got them here by the way, as they do look kind of sketchy: https://www.aliexpress.us/item/3256806577569338.html |
Posted by: d3jsp on 2025-09-26 17:40:40
Yup, turns out to be the 7052a. Looking around these seem to fail pretty frequently. Also, beware of fake chips from China, glad it didn't fry my board. |
Posted by: croissantking on 2025-09-27 03:07:11
Got them here by the way, as they do look kind of sketchy: https://www.aliexpress.us/item/3256806577569338.html
I need to get the same chip for my LC475. Just to confirm, it’s safe to buy from this link? |
Posted by: d3jsp on 2025-09-27 03:12:25
no, do not buy from there, they sell fake chips |
Posted by: croissantking on 2025-09-27 03:13:23
no, do not buy from there, they sell fake chips Ah, Ok. Do you have a link for legit chips? |
Posted by: d3jsp on 2025-09-27 03:14:02
look on ebay and buy the ones where they have pictures with chips made by NXP or Philips |
| 1 |