Help, can't figure out what resistors these are

[Nagamitsu]

Fried my car amp the other day, there's four resistors that are toast. I'm having a problem figuring out what these are, in order to purchase/order some.

To me, the lines almost look like: brown (or deep red), green, green, metallic brown.

The band that's usually gold or silver, looks metallic brown. Amp is a PPI Pro-Mos 425 (4 channel amp).

In sunlight, with a magnifying glass, they look:

Silver, black, black, brown (10 ohm, 10%)
Gold, black, black, brown (10 ohm, 5%)

Thanks in advance,

Tim

[Frank Berry]

It doesn't look like they're completely gone. Pull them and measure the resistance.
Something caused them to get hot. Replacing the resistors won't solve the problem.

[Nagamitsu]

Thanks! The two in picture in particular, got hot enough to burn the casing of a wire that was above it, wire appears in tact still though. Resistors off, they both read (meter set at 200) 11.4 or so.

Only 4 of these in the board, and all four look burnt/discoloured, nothing else on board looks bad. Maybe I'll solder them back on, and power it up (just power) and see. I shut off ignition when realized there was something not right, put ignition on again after a few minutes to see if power light on amp, and there was no longer.

Tim

[Perry Babin]

They are part of the Zobel networks on the output of each channel. They are 10 ohms. Check the capacitors next to each one to see if they're shorted.

[Nagamitsu]

Thanks Perry, they seem ok, and are the only ones appearing to have gotten hot enough to smell burnt. Testing power to the amp again tonight, will see if I get anything.

Tim

[Nagamitsu]

Good news and bad news. Good news, the amp still works, and still powers speakers.

Bad news, for some reason power light stays on after turning off ignition, the ignition/accessory wire is connected using same feed as my second amp, and the second amp powers off.

Get a bit of a "pop" when the radio/ignition comes on basically, didn't experience this before. Sound is not quite the best, but this install is with a different car from were I had it installed before.

One of my front components crackles a lot when volume increased. (unsure if now just a bad speaker, and not the amp causing this)

Tim

P.S, Perry, how can I test the capacitors for a short? The green components next to these resistors correct?

[Perry Babin]

Test the capacitors with the meter set to ohms. The resistance shouldn't be anything near 0 ohms. I'd expect it to be in the thousands of ohms at least. Out of the board, they should read open.

Do you have an oscilloscope?

[Nagamitsu]

Thank you. Well, I think I put the amp further in its grave. Everything initially seemed fine, then lots of crackle in the speakers, and more smoke from the amp.

The only thing different in this whole scenario is the car. But I probably damaged the amp when I had it hooked up wrong (bad ground, wired to what I thought was the speaker wire at the radio, but those were wires fed to the factory amp). I think that started the damage.

Hooked it up correctly last night, wired to the speaker wires exiting the factory amp (that go direct to the speakers), had sound. Apart from the amp staying powered on (symptom of having damaged in first place?) I had sound, but like I said now, driving this morning crackling got worse so I stopped and the amp was hot and starting to smoke.

Tim

[Nagamitsu]

Resistors appear to be still ok, reading what they should be, just that they were the components heating up quite badly.

The first set of capacitors are dead I think, on board one gives a quick reading then "0" or nothing, second one does not show any reading. The other two across on the board near the same set of resistors, both capacitors read around 700

Tim

[Perry Babin]

You'll need to check the capacitors out of the board and replace the ones that are defective before you can do any more troubleshooting.

What smoked in the amp? That type of resistor generally doesn't smoke much when it burns and you wouldn't be able to tell it was burning if the cover was on the amp.