Pyle PTA2 - Schematic, or Just Identify the Part?

[g1]

If the zener is from a supply rail to ground, that supply rail would be zero with the zener shorted. Odd then for the amp to be working ok, just with a bit of extra hum.

[The Dude]

I assumed, maybe wrongly, that he removed the zener and was running the unit without it for testing. Again, I could be wrong.

[Toolworker]

I assumed, maybe wrongly, that he removed the zener and was running the unit without it for testing. Again, I could be wrong.

No, I haven't turned it on since I opened it up. I removed the zener to measure it.

Here are pix of the board, with links to very high resolution versions. The middle one has an inset that shows the front panel components that aren't visible from the top.

Composite image (high resolution):



Component side (high resolution)



Trace side (high resolution) - flipped horizontally to correspond to the image above.

[The Dude]

Looks to me like that supply goes through a 100 ohm resistor to the -V op amp pins, so it should be the negative supply for the op amps. The zener was probably 12-15V. Check pin 8 of the op amps and see what that voltage is and use it for comparison. It should be the complimentary positive supply. If that's 15V positive, then the negative supply should be approximately the same- if 12V, then use 12, etc. Get a zener that's approximately the same voltage. Be sure to observe proper polarity for a negative supply.

Edit: I also noticed in the pic that you can sort of read a part number where the diode sat on the burnt board. Can you glean anything from that?

[Toolworker]

Looks to me like that supply goes through a 100 ohm resistor to the -V op amp pins, so it should be the negative supply for the op amps. The zener was probably 12-15V. Check pin 8 of the op amps and see what that voltage is and use it for comparison. It should be the complimentary positive supply. If that's 15V positive, then the negative supply should be approximately the same- if 12V, then use 12, etc. Get a zener that's approximately the same voltage. Be sure to observe proper polarity for a negative supply.

So should I replace the resistor, leave the zener out, and measure pin 8 of the op amps?

The blue wiring feeding this circuit is labeled 10v on the transformer.

Edit: I also noticed in the pic that you can sort of read a part number where the diode sat on the burnt board. Can you glean anything from that?

Yes, I just noticed that on the photo. Here's a better lit image:



Google didn't turn up anything for 1W8J2.

[The Dude]

That's 1W8V2. There we go! It's a 1 watt 8.2V zener. Here's a good cross.

https://www.mouser.com/ProductDetail...qjX5pYmg%3D%3D

[Toolworker]

Awesome! Thank you SO much!

What do you think about getting a 5W diode just in case it was marginally spec'd?

Would you avoid eBay?

[The Dude]

Lots of fake Chinese parts on eBay. I'd go with a reputable seller on something so commonly available. IMO, it wouldn't hurt to up the power rating, slightly, maybe 1.5 or 2W. I think 5W is overkill plus leads will likely be larger and it'll be a bit of a pain to install without drilling, etc.

[Toolworker]

Parts ordered. Will report following smoke test. Thanks again!

[Toolworker]

The zener and resistor have been replaced. (The zener choices were 1.8w and 5w so I went with 5w.)

With power on, the zener gets hot.




Some measurements:

• 8.52v across the zener diode; scope shows no ripple.
• 1.3v across the resistor
• 150 ma ac out of the transformer
• The diodes measure 0.5v / 0v with the multitester (power off)

I don't know enough to look further, but will try to follow any suggestions.

[Helmholtz]

Measurements look ok. Zener is dissipating 1.1W, so it will get hot to the touch.

[Toolworker]

Measurements look ok. Zener is dissipating 1.1W, so it will get hot to the touch.

Thanks for the encouragement. No smoke after 20 minutes, so it's back together and working.

It's a 1 watt 8.2V zener.

So if the original part was dissipating 1.1W, maybe it fried, shorted, and took out the resistor.

Now it's got a 5 watt zener and a 2 watt resistor, spaced off the circuit board. I'll call it fixed unless it tells me otherwise.

The Dude - thanks so much for all your help!

[Helmholtz]

Problem with small sized components that have to dissipate something like 1W is that their leads get very hot.
When mounted with short leads they considerably heat up the solder joints which may cause the solder to deteriorate, increase resistance and fail over time.
The additional heat by increased joint resistance and arcing may eventually destroy the component.

[Toolworker]

I just want to thank The Dude and everyone else. The amp has been working great. I added a subwoofer and am really enjoying the system. It couldn't have been fixed without your help.

[Mike in Wis.]

New to the group.... I just wanted to say thanks for theis post, the pics and information. I have the same Pyle PTA2 and experienced exactly the same failure of the same two components last week. I have to parts ordered, and look forward to getting the PTA2 repaired. I'm curious if this repair lasted the roughly 1 year since the last post ?

Regards,

Mike