Bose Wave Radio/CD Loud Popping and Crackling

[fuzzoli]

I've got a Bose Wave Radio/CD with the speakers popping and crackling when not muted.  I've hit most of the normal troubleshooting endpoints:
- It does appear something had spilled into the radio at one point.  All the crud was cleaned up.  Cleaning under the film (rectangular) caps was not possible (call me lazy)>
- The initial problem is the left speaker didn't produce any sound.  After cleaning, both sides worked, but now getting the popping.
- Electrolytics on power-related pins for the amp (TDA7375A) have been replaced.
- Electrolytics on the main power rail (V, VMOTOR) replaced.
- Electrolytics filtering VCC (C685) and CREF (C642) replaced.
- Crackling / popping (C/P) is on the Line Out RCA jacks as well as the speakers.
- C/P corresponds to significant spikes on the analog supplies; digital supplies seem OK.
- C/P on any input selection mode
- Did not replace the series caps (C647/650) going from the input selector chip (TDA7313) and the equalizer circuits.
- Swapped speakers; same results.
- Single speaker; same results.
-
- At one point, a cold radio behaved worse, but I can't heat up any parts to make the issue go away (tried heading the regulators too).

Short of replacing all the caps, is there anywhere else I should be looking?  I'm not much of an analog guy.

Thanks!

[Jeff eelcr]

Most likley clean better and caps not knowing what year it was made.
Jeff

[elecdonia]

Pardon me for rephrasing some questions which you previously answered:

1)    Does increasing/decreasing the loudness by using the volume up/down buttons change the loudness of the popping/crackling noise?
2)    Is crackling noise still heard with very low volume (1-5)?    (note: volume control may work differently than mute button -- for some models mute button switches off power output IC, but volume buttons do not, except when volume level is 0)
3)    Is radio able to receive over-the-air broadcast stations with good sensitivity, both AM and FM?
4)    How well does the CD player work?
5)    Does playing a CD change the sound of the popping/crackling noises (I'm wondering about electrical noise generated by the CD player spindle motor, or by the loading motor if this unit has a slot on the front to slide the CD into)
6)    With medium volume (20-30), does changing between radio , CD, or line input mode cause any change to popping/crackling noise loudness or pattern?

[elecdonia]

- It does appear something had spilled into the radio at one point.

I successfully repaired a wave radio which had an extensive cockroach infestation. Fortunately it didn't contain any live insects when I got it. 

This was an older model (radio only, no CD player). It had metal shield covers over some sections of the PC board. I removed these to clean underneath and then put them back on.

I scrubbed both sides of all PC boards with a toothbrush and isopropyl alcohol. I followed this by extensive rinsing with hot tap water, then shook off most of the water followed by blowing off more water with air duster. After inspection I saw a couple of really nasty locations on the PC board that weren't totally clean yet. I unsoldered/removed a couple of metal shields and then repeated the iso alcohol scrub, hot water rinse, and blow dry. Finally I allowed it to air-dry for several days before powering up.

[elecdonia]

- Electrolytics filtering VCC (C685) and CREF (C642) replaced.
- Crackling / popping (C/P) is on the Line Out RCA jacks as well as the speakers.
- C/P corresponds to significant spikes on the analog supplies; digital supplies seem OK.
- C/P on any input selection mode

Is C686 (470uF) the capacitor you replaced on the VCC power supply rail (pin 2 of TDA7313)?

If crackling/popping still persists after everything is totally clean and dry, then IC TDA7313 might be faulty.

Also, if there was lots of contamination/dirt near the TDA7313, then there could still be residual contamination underneath the IC chip. At times I desoldered an IC chip in order to get the PC board underneath sufficiently clean. In the case of desoldering the TDA7313 for this purpose it would be a good idea to obtain a replacement TDA7313 IC just in case the original IC has actually failed. Note: I use "chipquick" low-temperature alloy when desoldering parts like the TDA7313. I've found Bose PC boards to be somewhat delicate: their foils are narrow and the pads are small. I don't want to damage the PC board when I replace components. Chipquick desoldering alloy works very well for this. Only a small amount is needed. Spread some rosin flux on the IC pins, then melt a bit of the chipquick onto each IC pin with a soldering iron. Then a heat gun or hot-air rework gun will melt the chipquick alloy very quickly. The IC chip will lift right off leaving the PC board in perfect condition. Then use desoldering wick to remove all vestiges of old solder and chipquick before reassembly.   

The TDA7313 operates entirely on a single positive rail voltage filtered by C686 and input into pin 2.  The IC contains an internal regulator filtered by C642. The DC voltage at pin 1 (CREF) should be approximately 1/2 of the DC voltage at pin 2. The TDA7313 does not use a negative rail supply.

I recommend re-checking the polarity of the replaced capacitors C686 and C642
Also please measure the DC voltages at TDA7313 pins 1 and 2 and post them. According to datasheet the ideal supply voltage for the TDA7313 at pin 2 is 9.0V

I attached TDA7313 datasheet.