Recognizing part maybe TVS diode?!

Hi guys
I'm missing SA501 and SA502. Are these a TVS diodes ? They were badly burnt but I could still read something like 3 stripes red green red. I highly doubt it's a 3 band resistor of 2.5KΩ. They are being used in the preamps section in between the RCA shield and the secondary ground of the transformer. I 've also found that the traces from the secondary gnd to the RCA shield have been blown up.
The amp is Philips xp480. I do not have the schematics.
Any ideas ?
 

Attachments

  • diode.jpg
    diode.jpg
    797.5 KB · Views: 122
Sadly no. i've even had to google what is variac. never needed one so far.
I'm not 100% sure if this is my issue, but since the blown secondary gnd trace to the TVS and the soot the in them, I thought this was it
For sure it's a pre-amp issue, nothing reach the op amps (the have the proper +/-15v) all 4 channels.
Injecting signal into the amplifier section bypassing the preamp works.
 

Attachments

  • 1.jpg
    1.jpg
    964.9 KB · Views: 71
  • 2.jpg
    2.jpg
    975.7 KB · Views: 72
Do you see any signal on the RCA terminals where they go into the board?

Does that signal reach the other end of the wires for the preamp signal?

As a side note, the colors for the TVS are orange on both ends and that's simply the material that the device is made of. It's the same orange as on other glass diodes. The only stripe is green and you may never know what that means.

One more note. If you come across a cheap variac, buy it. Variac + bridge rectifier and capacitor = good high voltage variable DC supply.
 
Last edited:
Sometimes You get lucky....
I've received two more amps for a repair...one of them is flea market no name, no markings....the other one is Philips dap 4040 which i was able to find the service manual for.

3 of them are identical 1:1 to the slightest detail. Three of them has the exact same issue.

Attached is the full service manual.

SA 501 and SA502 are surge protectors.

Sinewave disappears once it enters the Q101/Q201/Q301/Q401 - 2SC2712. I've already swapped those with a new ones. Same sh*t.
If I inject the sinewave directly at R106/R206/R306/R406 - amp plays just fine.

I feel like something is dragging the signal to ground...maybe Q519 ?
 

Attachments

  • philips_22dap4040-00_sm.pdf
    3 MB · Views: 49
Looking at the service manual...

Q101/Q201/Q301/Q401 - mines are all 15.2v across all pins but service manual says completely different thing (picture attached)

Q519:
B: 15.8v
C: 15.8v
E: 15.35v

So does Q519 even work at a 0.45v, should be this figure at least 0.6v ?

I've measured for resistors out of tolerance but could not find any...
 

Attachments

  • q.JPG
    q.JPG
    5.2 KB · Views: 30
  • q519.JPG
    q519.JPG
    3.8 KB · Views: 30