Spectra noisy audio

MP 6.7 · Post by **MP 6.7** » Sun Jul 18, 2010 12:50 am

I have new caps on order for my Spectra to fix the popping audio...but there's also a bit of noise in the speaker whenever the audio amp is on. It seems to be temperature and humidity dependent. Do bad caps to this too or is something else dying on that board? (read: should I just replace the board?)

wa6ylb · Post by **wa6ylb** » Sun Jul 18, 2010 6:14 am

Look at the legs of the audio chip. If you see they are blackened legs right next to the IC black body itself, you need to replace the audio IC. These chips will exhibit the popping noise when they start to go bad. I've even seen them ooze something out the legs (hence the blackness on the legs - not to be confused with tarnishing silver legs).
B.

Bill_G · Post by **Bill_G** » Sun Jul 18, 2010 7:56 am

The caps on the command board can eat up traces, bypass caps, and snubber resistors enough to cause all kinds of audio problems. Sometimes you really have to scrutinize the boards, clean them thoroughly, and put a lot of effort into repairing traces to make them right again.

MP 6.7 · Post by **MP 6.7** » Mon Jul 19, 2010 12:21 pm

The caps next to the audio IC haven't done too much visible damage. We'll see if they really have once they come off. A few of the pins on the front of the radio side of the IC have brownish stuff on them, see photo.

Bill_G · Post by **Bill_G** » Mon Jul 19, 2010 12:54 pm

That's exactly what wa6ylb was talking about. Time to replace the audio PA. Time to change caps too. The large 10uF is eating up the traces to the two yellow tantalums which are part of the snubber that keeps the audio PA from overheating from ultrasonic oscillations. You got a two-fer.

MP 6.7 · Post by **MP 6.7** » Mon Jul 19, 2010 1:21 pm

Bill_G wrote:That's exactly what wa6ylb was talking about. Time to replace the audio PA. Time to change caps too. The large 10uF is eating up the traces to the two yellow tantalums which are part of the snubber that keeps the audio PA from overheating from ultrasonic oscillations. You got a two-fer.

Kind of what I figured. I noticed the TDA7256's available at Mouser, etc. are 11 pins...is the 15 pin version a Motorola custom part? I think I read that on here somewhere. I might just end up replacing the command board if I can find one cheaply.

Bill_G · Post by **Bill_G** » Mon Jul 19, 2010 1:37 pm

I'm not too far south of you. Pretty easy fix. Let me know.

maxkelley_kc2spy · Post by **maxkelley_kc2spy** » Mon Jul 19, 2010 5:52 pm

Does anyone have the Motorola part number for their 15-pin TDA7256? The Motorola 15-pin 7256 is actually, so I've heard, a 7255 in disguise.

Ooh! Just looked on eBay, someone's selling the TDA7255s for $9.58 plus $3 shipping. http://cgi.ebay.com/TDA7255-Integrated- ... 0248757476 Not bad, I suppose...
And 15-pin TDA7256 for $7 with $6 shipping. http://cgi.ebay.com/TDA7256-STM-30W-POW ... 097wt_1139 Interesting!

Mine's got green crud on it... Probably needs replacing!

arlojanis · Post by **arlojanis** » Tue Jul 20, 2010 6:24 am

I have a new 5180065C19 15 pin IC. This replaces the C17 old number for IC. PM me for details.

Will · Post by **Will** » Tue Jul 20, 2010 4:05 pm

Too bad the caps already leaked and moderate damage is visible. The audio chip looks bad from the crud on the pins.
Remove the four silver caps and the two orange tants and clean the board thoroughly.
Easy to replace the IC and the 'silver' electrolytic caps with leaded tant caps. The two orange tants were changed to 1.0 uF ceramic chip caps in later production.

If that is a challenge, I replace the electrolytics with surface mount Mil spec tants here. I also replace the two 'snuber caps' with SM ceramic chip caps and the two resistors too.

Seems Arlo has the audio IC you need.

Bill_G · Post by **Bill_G** » Tue Jul 20, 2010 6:19 pm

I've seen worse. Definitely run a piece of nichrome wire through the worst plated eyelet. Looks like it might be recovered by simply reflowing, but running the wire through will help clear it. You'll know soon enough since you have to pull the board to replace the pa. Good times.

MP 6.7 · Post by **MP 6.7** » Wed Jul 21, 2010 12:00 am

Thanks for all the info. I'll look further into sourcing parts in a couple weeks as I'm leaving for toasty DC tomorrow and won't be working on any radios until I'm back

I think it's worth it on this radio since the RF section is just about perfect and once we all go narrowband it'll be turned into a 2 meter ham rig.

Tishers · Post by **Tishers** » Mon Aug 09, 2010 9:32 am

maxkelley_kc2spy wrote:Does anyone have the Motorola part number for their 15-pin TDA7256? The Motorola 15-pin 7256 is actually, so I've heard, a 7255 in disguise.

Ooh! Just looked on eBay, someone's selling the TDA7255s for $9.58 plus $3 shipping. http://cgi.ebay.com/TDA7255-Integrated- ... 0248757476 Not bad, I suppose...
And 15-pin TDA7256 for $7 with $6 shipping. http://cgi.ebay.com/TDA7256-STM-30W-POW ... 097wt_1139 Interesting!

Mine's got green crud on it... Probably needs replacing!

As that is a bit of a weirdo amp I too would like to know if there is a non-moto equivalent part. I am certain that they do not cast their own IC's in subbasement U of the Schaumberg office.

MP 6.7 · Post by **MP 6.7** » Mon Aug 09, 2010 10:46 am

My package from Mouser arrived so I changed out all the caps in the sick Spectra. All boards were a breeze with minimal damage except for the command board. Two of the 10uF caps had leaked badly enough to lift the solder pads and a little of their traces, so I had to solder the new caps to alternate points. The loud pops are gone and the noise is greatly reduced, but it's still there so I'm going to go ahead and replace the audio IC. Everything got thoroughly cleaned with liberal amounts of isopropyl before soldering the new caps on.

maxkelley_kc2spy · Post by **maxkelley_kc2spy** » Fri Nov 05, 2010 9:23 pm

Sorry to bring up an old topic, but I just got a replacement TDA7256 (15-pin) for my Spectra, installed it, and it seemed to make the audio sound a little cleaner, but there is *definitely* a pronounced popping when the audio amplifier is enabled (squelch opens, button press, etc). Would this be caused by the orange tantalums? And *which* of the orange tantalums in the picture above would be them?

I did already replace all my electrolytics. That was the first thing I did, back in the summer. Then, today I finally replaced the audio IC after dealing with noisy, distorted audio for a while... And now we have popping!

Bill_G · Post by **Bill_G** » Sat Nov 06, 2010 6:30 am

Check all the plated eyelets especially under and near the large 10uf cap. Also check the pads for the two yellow caps to the left of the 10uf. All the solder should shine. If it is the least bit dull, it has been attacked by the cap ooze, and needs to be (at least) reflowed. You should probably lift the command board back out to inspect for ooze that may have crept to the other side through an eyelet. It will look like an oil stain, and you may find more damaged eyelets that need to be repaired.

Spectra noisy audio

Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio

Re: Spectra noisy audio