Lost a channel [resolved]

[portway]

Hi,
I have been running my BeePre/BeeQuiet for a couple of weeks now and absolutely love the sound. Unfortunately, yesterday for no obvious reason I lost one channel. After all the usual checks, swapping valves (one pair at a time), checking and replacing my interconnects and switching sources the problem is narrowed down to the BeePre itself. Looking at the underside the LEDs on one channel are no longer illuminated. All of the regulators are tight to the heatsinks and I can't see any burned or charred components. I am a kit builder and not an engineer so suggestions to remedy this problem are very welcome.
Thanks
Tony

 

[fullheadofnothing]

Redo resistance and voltage checks. Post results.

 

[portway]

Thanks for the reply and I will do. Maybe a few days though due to committments

 

[portway]

Redo resistance and voltage checks. Post results.

Hi again - at last had the chance to investigate the channel dropout.
Funny thing is on powering up I now notice all 8 leds are alight. So before any further exploration I have reconnected the BeePre and its working again no idea whats happened. If it decides to go down again I will of course report back with resistances and voltages.

Thanks for your attention.

Tony.

 

[portway]

Redo resistance and voltage checks. Post results.

Well, this problem has recurred, Occasionally I can get both channels to work but this is certainly a big problem. I include the resistance and voltages below but my suspicion is a faulty 220uf capacitor on 15U. As far as I can see all of my soldering is good and the fault occurs either immediately on switch on or after several hours of use. Again your help would be greatly appreciated.

Resistances:
1. 4.2 Ohms
2. > 3 Meg Ohms
3. 0 Ohms
4. Unstable
5. 0 Ohms
6. 145K Ohms
7. 460K Ohms
8. 0 Ohms
9. 0 Ohms
10. 20K+ Ohms
11. 156K Ohms
12. 471K Ohms
13. 0 Ohms
14. 0 Ohms
15. OL? Open Circuit.
16. 4.2 Ohms
17. OL
18. 0 Ohms
19. Unstable
20. 0 Ohms
21. 0 Ohms
22. 0.4 Meg Ohms
23. 0 Ohms
24. 0 Ohms
25. 0.47 Meg Ohms
26. 0 Ohms
27. 0 Ohms
28. 0 Ohms
29. *
30. *
31. *
32. 0 Ohms
33. 0 Ohms
34. *
35. *
36. *
37. 0 Ohms
38. 0 Ohms
39. 0 Ohms
40. OL
41. 0 Ohms
42. 0 Ohms
43. 28 Meg Ohms
44. 0 Ohms
45. 0 Ohms
46. OL
47. N/A
48. 603 Ohms
49. 0 Ohms
50. N/A
51. 603 Ohms

A1. CONSTANT 0.8 K Ohms?
A2. 3 Meg Ohms
A3. OK
A4. Not Tested
B1. Not Tested
B3. OK
B4. 1K Ohms? Very slowly dropping

C1, D1. N/A
C2, D2. 216 Ohms, 214.5 Ohms.
C3, D3. OL, OL.
C4, D4. >100 Ohms, >100 Ohms
C5, D5. >100 Ohms, >100 Ohms
C6, D6. N/A
C7, D7. >30K Ohms, >30K Ohms
C8, D8. N/A
C9, D9. 140K Ohms, 140K Ohms

Voltages:
1. 4.9v
2. 92.9v
3. 0v
4. 9.85v
5. 0.007v
6. 145.1v
7. 0v
8. 0v
9. 0v
10. 169.8v (a bit low?)
11. 145.1v
12. 0v
13. 0v
14. 0v
15. 184.9v
16. 4.96v
17. 91.6v
18. 0v
19. 9.84v
20. 0.007v
21. 0v
22. 197.4v (low?)
23. 0.007v
24. 0.007v
25. 193.4v (low?)
26. 0v
27. 0v
28. 0.05v
29. 6.62v
30. 6.63v
31. 13.27v
32. 0v
33. 0v
34. 13.25v
35. 6.8v
36. 6.8v
37. 0.043v
38. 0v
39. 0v
40. 208.3v
41. 0.009v
42. 0.009v
43. 208v
44. 0v
45. 0v
46. 212.1v
47. N/A
48. 0v
49. 0v
50. N/A
51. 0v

A1.
A2. 92.5v
A3. 0v
A4.

B1.
B2. 91.6v
B3. 0v
B4.

C1, D1. N/A
C2, D2. 0
C3, D3. 4.46v, 4.12v
C4, D4. N/A
C5, D5. N/A
C6, D6. N/A
C7, D7. 145v, 145v
C8, D8. N/A
C9, D9. 145v, 145v

 

[Paul Birkeland]

What is your AC line voltage?

You can't have one side with no LED's and have the perfect voltages that you have, both conditions can't be true simultaneously.

From what information is available, you likely have a flaky solder joint on a component that is key for passing AC signal, not not DC current.  These types of components include the 10uF coupling caps, the input attenuator, and their associated solder joints.

-PB

 

[portway]

Voltage = 235.3 v ac

I will check my soldering again but not before friday as I am on shift till then. So the itermittant fault means either both channels are ok or if only one then one channel diodes are not lighting. One final clue, yesterday after switch on only one channel again until I tapped the top plate then both. Today this hasn't worked.

 

[Doc B]

Something coming back to life when tapping on the chassis is most likely to be an intermittent connection like a missed solder joint or a component lead that didn't get trimmed and is intermittently grounding against something. There is a slim possibility that it could be a tube problem, but that is not nearly as likely based upon your description.

 

[portway]

Thanks Doc, I will do a complete solder and lead check as soon as the holiday comes.

 

[Paul Birkeland]

Voltage = 235.3 v ac

I will check my soldering again but not before friday as I am on shift till then. So the itermittant fault means either both channels are ok or if only one then one channel diodes are not lighting. One final clue, yesterday after switch on only one channel again until I tapped the top plate then both. Today this hasn't worked.

Yeah, you have perfect voltages, at least from what you posted.  Next time you check voltages, you can try tapping on the chassis to see if any of the LED strings turn off.  That can narrow things down for you a little bit.

 

[portway]

Hopefully I have now found and corrected the problem. Turns out that on further inspection on removing the C4S board the white wire had in fact broken inside its sleeve close to 15U. So tapping seems to have sometimes made contact. Anyway the problem does now with resoldering seem resolved. Thank you all for your input.
Tony.

 

[Paul Birkeland]

Well done!  It can be pretty tough to find a broken wire.