Stereo Amp 52280-A

[fooch]

I have a Mystic 478 with an amplifier going into Speaker Overload protection as soon as the needle touches record.  I believe I have traced the issue to PEC8 (Part# 52357).  Anyone have any tips on testing this sealed part?

[jukenorman]

Hi Frank,
Jukebox Revival in The Netherlands does a replacement for that PEC.

Norman.

[fooch]

Hi Norman
Yes I have seen that but to purchase and have it shipped to Canada will cost me $50. I was hoping to find a schematic to build it myself. But thank you.

[jukenorman]

Hi Frank,
There is a "rough" diagram in the large fold schematic that came with the original manual which is attached. Don't forget to let us know how you get on with your build!

Norman.

[fooch]

Norman
This is excellent. I purchased the manual online but did not come across this page ( manual appears to be reprint as it does not have foldouts). Does it have any component values listed for diodes and transistors?

[jukenorman]

Hi Frank,
No component list. Looking at the Jukebox Revival picture, it looks like they have used something like 1N4148 for all the diodes except the one connected to pin 2 where they have used something beefier, 1N4001 maybe? Probably just a couple of GP transistors - 2N3904 and 2N3906 possibly would be OK? If you build it, you must let us know whether it works!

Norman

[fooch]

Hi Norman
I agree with the transistors but the diodes (aside from the one on Pin #2) appear to be Zener diodes although the schematic symbols do not indicate that. Looking at the picture from Jukebox Revival site. www.jukebox-revival.eu/rockola-p-e-c-52357-protection-circuit.html

[jukenorman]

Hi Frank,
I can't see these being zener diodes - that's a lot of zeners in a circuit with only a hanful of components! The one connected to pin 2 surely couldn't be a zener because it's biased in the same direction as the (agreed) probable 1N4001 connected to pin 1? The two in the middle, aren't the voltages the wrong polarity for zeners to be able to conduct (the bold line is ground)? And finally, on the large schematic where zeners have been used, they have been drawn diagramatically correct.

Norman.

[fooch]

Norman
I agree, that for such a small circuit that would suggest a lot of Zener diodes. However, on the Jukebox-Revival webpage, they show the circuit board and you can clearly see 4 Zener diodes. I may need to investigate this further.

[fooch]

Hi Norman
I wanted to update that the 1N4148 looks like the Zener (Orange clear). Also, the transistors are MPS A06 and MPS A56. I have just ordered them and once I build the two boards and test, I will report my findings. Thanks for all your help.

[carlski]

Hi total novice here
Hope this might help
this part didnt do what I was expecting but is correct to schematic provided by norman (apart from 3x 1k ohm not 2x1k and a 5.6k)which supplier confirmed should have a 5.6k
shows diodes are different to linked example you have??
sorry having trouble linking picture will edit again soon to fix

[Ron Rich]

Hi Carl,
I see where you have red, red, red--or is that read, read, read---- (so goot I'm not, at spelling !). Nice photo-- can you "read" the numbers on all the diodes ?? Ron Rich

[carlski]

Hi Ron
as best I can see with glasses and large mag glass.
Small diodes 1n4148

large ends in 007 and has a C under
                       C

Not ready to deconstruct it yet as have removed one transistor to test and wrecked traces on board(have fixed with solid traces)
I will have to replace the wrong resistor though

 Transistors MPSA           MPSA
                    06               56
                 57 c              RD C

Cap             153k
             jb
                  630v

Resistors         2x 1k        1x 5.6k

[Ron Rich]

Hi Carl,
Thanks--
I'm Guessing here-- the "007 C" is a 1N4007 diode --dono what the "C" signifies ?
!N4148 --I THINK, is a "generic signal diode" ?
The MPS trannies are multi purpose transistors--NPN/PNP
Ron Rich