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RiLoWa 24th April 2012 02:42 AM

Memphis 16-PR1KD
This amp will briefly cycle audio output and then quit cycling and remain silent. Only the power LED is lit, the other LEDs are off.

Here is what I have on the 494
1: .620V
2: 4.21V
3: .076V
4: .469V
5: 1.531V
6: 3.487V
7: .0157V
8: 13.66V
9: .0156V
10: .0156V
11: 13.66V
12: 13.68V
13: 4.97V
14: 4.97V
15: 4.97V
16: .0156

Q19 and Q33 get hot to the touch.

Perry Babin 24th April 2012 10:42 AM

Do you have rail-rail oscillation on the output transistors when it's producing audio and when it's not producing audio?

RiLoWa 24th April 2012 12:29 PM

When this amp produces audio, it is very brief. It will be difficult to test it while audio is present.

I did see oscillation (very briefly) and then nothing. The scope was set at 50V div. and 10uS and I would be guessing that it was about 1 division peak to peak that I saw.

Perry Babin 24th April 2012 02:53 PM

These amplifiers (like many of the clones) have problems with transistors overheating. I'd replace any of the transistors that have solder connections that show signs of heat stress. The drivers are also suspect. I'd suggest replacing those as well. They are the 8 transistors closest to the output transistors. If that doesn't solve the problem, you'll need to check voltage across various components.

To make this amp reliable, you'll need to install heatsinks on the driver transistors.

RiLoWa 24th April 2012 10:39 PM

In another thread, it was recommended to replace the MPSA42s with MPSW42s. Would it be the same logic switching the MPSA56s with MPSW56s also?

Are there suitable substitutes for the C3227, C3200, and A1275?
If so, would it make it better to go with a slightly larger package like a TO-126 for the C3227 and A1275?

Perry Babin 24th April 2012 10:46 PM

The W42s operate at the highest temperatures for the drivers so those should be replaced with the W version. You can replace the A56s with W56s if you have them.

I think the substitution would depend on the application. Transistors used in the switching part of the class D circuit will be more critical than those used in non-switching applications.

Larger packages will be able to dissipate more heat. Install the transistors a bit higher than you normally would to prevent the board from being damaged from the heat.

RiLoWa 25th April 2012 12:34 AM

I come up with KSA1013OTA for the 2SA1275 as a good sub.

It would appear that an MPSW06 might sub for the 2SC3227 if the legs were ECB instead of EBC.

I do not find a suitable sub for the 2SC3200.

The two harder to find parts are the two that heat up the most as the amp sits right now.

Perry Babin 25th April 2012 12:38 AM

In some of these amps, I used a KSA1220A in place of the a1275.

What's the circuit board designation for the c3200?

RiLoWa 25th April 2012 01:13 AM

There are two C3200s, Q19 and Q18. It is Q19 that gets hot.

Q33 is the C3227 that gets hot.

The data sheets look almost identical on the 1013 to replace 1275 (Q21) unless I am not looking far enough into the specification. I will note the A1220 as a possible.

All of these are in the transistor array behind the eight driver A56s & A42s.

I found a place that claims to have the correct part numbers on hand (C3200 & C3227), but I have never done business with them.

RiLoWa 25th April 2012 01:24 AM

Maybe a BD139 in place of the C3227 at Q33?

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