Electronics > Repair

Yamaha VSS-30 Repair- Selecting Components

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scsijims:
Hi all, just joined. Hope I'm in the right place and following the rules (didn't see a rules sticky for this sub-forum, so please let me know).
I have been learning to solder by repairing cheap samplers (well, they used to be cheap--prices have gone through the roof).
This will be my first diagnose and repair job. My other repairs have involved screen replacements and scsi mods which are fairly straight forward.

Here's the situation:
I purchased a Yamaha VSS-30 off ebay to use for parts. Seller says they plugged in the wrong power supply and it doesn't turn on.

So far, I have disassembled the unit and identified 2 possible issues:
1. A bulging 25v 1000uF electrolytic capacitor (Image 1). It is 16x16mm and approx 8.3mm lead spacing.
-Question 1: I watched some videos and read about recapping but I'm a little confused. I read that the lifespan of these types of capacitors is about 5 years. Should I consider a different type? or is that just the nature of the beast with vintage electronics?

2. A blown? IC reading "AN7140 70.6" (Image 2) according to the data sheet a "5w Audio Power Amplifier Circuit." The service manual identifies the chip as "AN7140 (IG116800) 5W 1CH"
-Question 2: Any idea what the "70.6" may be referring to? I found some AN7140's on eBay, but they all have different numbers in that space- ".821" "56.6" etc. Not sure if these variations would make any difference. Any guesses?

There is also a common failure on these units that seems to be occurring on my other VSS that I read online can be corrected by replacing the DRAM:
3. DRAM (Image 3): In this unit, the IC reads "TMS426-15NL HG 731 56" with a Texas Instruments logo and the service manual refers to it as "MB81256 (IG155100) DRAM"
-Question 3: Is it reasonable to assume this is a manufacturer variant of the prescribed chip? I cannot find an exact replacement on the one on my board, but there seem to be "MB81256" IC's available such as the following:
https://www.ebay.com/itm/124578546425?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=124578546425&targetid=1264870804704&device=c&mktype=&googleloc=9007909&poi=&campaignid=14859008593&mkgroupid=130497710760&rlsatarget=pla-1264870804704&abcId=9300678&merchantid=118887875&gclid=CjwKCAjw2bmLBhBREiwAZ6ugo9vtXGDsmTcPv4axlqelqNbGn7Gfntw6-19Y58T3dQkAEhfaa5gO9BoCh48QAvD_BwE

-Question 4: In troubleshooting this possible DRAM issues on my other VSS, I wonder if it would make sense to remove the DRAM IC and solder a socket into its place to allow for swapping the original, one from the broken VSS, and possible replacements. What do you think?


I know this is a lot! My hope is that your answers will help me to understand the nuances of selecting replacement parts and and idea of how picky I ought to be. If you read this far, thank you for your time!!

Service manual: https://www.manualslib.com/manual/1214284/Yamaha-Portasound-Vss-30.html

Haenk:
The electrolytic caps can last for several decades, or only a couple of years. Depending on the manufacturer (Nichicon is one of the top manufacturers) and on the abuse (i.e. thermal or electrical use out of specifications).

The "70.6" is probably some batch or date code. Nothing to worry about.

Using different manufacturers with different part# is common on those DRAMs. It should not be a problem to source the exact same part#, just to be safe.

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