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Bought a Marantz PM7200 - dead channel

I think it just must not be in the main amp! I still have no right channel with headphones?

EDIT: Could it be something to do with the headphone socket?

Very odd stuff happening! On resistor 3356 with the headphones out I get no waveform at all. With headphones fully in I get very very small waveform. With it half in/out I get a normal one?
 
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Time for me to call it a night. Nothing makes sense, 7256 Vbe cant be more than 1.3V
CRO shows audio coming into power amp, 7252base. Headphones are normally after the power amp, same as spkrs.
 
mbz said:
Time for me to call it a night. Nothing makes sense, 7256 Vbe cant be more than 1.3V
CRO shows audio coming into power amp, 7252base. Headphones are normally after the power amp, same as spkrs.
Click to expand...

Yea frustrating for me too. I did measure exactly where you told me.

POS lead on diode and neg on resistor
 
Oh well fun and games over. I slipped with the Oscilloscope prob while measuring sine wave at transistor 7256 and shorted it out. Turned amp off immediately. When I turned it back on the 1207 fuse blew.

Flapping hell. I hope I only blew the transistor and didn't do any more damage :oops::(
 
If the transistor is ok where should be the first place to look for the stuff up I created?

EDIT: Transistor tested ok.......crap it....I've stuffed something else up :(:(:(:(:(:(
 
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Bugga

As best you can remember, what two points did the probe touch. Two transistor legs? (would kill the tr).
3276 (47K R) is in the area. Guessing shorted 7256e and 3276 leg directly beneath it. This would probably
take out both transistors 7258 and 7260. Both should be diode tested.

You will need a DBT when you next power up.
 
mbz said:
Bugga

As best you can remember, what two points did the probe touch. Two transistor legs? (would kill the tr).
3276 (47K R) is in the area. Guessing shorted 7256e and 3276 leg directly beneath it. This would probably
take out both transistors 7258 and 7260. Both should be diode tested.

You will need a DBT when you next power up.
Click to expand...


Yea that resistor is toast. Pulled it and it's not reading at all. Open cct.

Pulling and testing the 2 resistors now
 
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Yea that resistor is toast. Pulled it and it's not reading at all. Open cct.
With the resistor open you are still blowing fuses. Transistors 7258 and 7260 are suspect along with diodes 6258, 6260.
Also check transistor 7262, diode 6264.
You might be lucky with only 2-3 transistors down and 2 diodes??
 
mbz said:
Transistors 7258 and 7260 are suspect along with diodes 6258, 6260.
Also check transistor 7262, diode 6264.
You might be lucky with only 2-3 transistors down and 2 diodes??
Click to expand...


Transistor 7260 fried.....

EDIT: 7258 also dead

EDIT2: Diodes 6258, 6260 and 6264 are good

EDIT3: Transistor 7262 good
 
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7258, 7260, 2SA970, replacement KSA992.
Need to replace both 7260 and 7258 with hfe matched pair

Transistors can fail open or short, hopefully you find one that's failed short, explaining why fuse is blowing.
 
mbz said:
7258, 7260, 2SA970, replacement KSA992.
Need to replace both 7260 and 7258 with hfe matched pair

Transistors can fail open or short, hopefully you find one that's failed short, explaining why fuse is blowing.
Click to expand...

Thanks mate. What is an hfe matching pair? Why is it required? Can I get from Jaycar? Hoping to fix this amp while I'm on holidays so not much time for getting parts from O/S.
 
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hfe, also called beta is the gain of the transistor. Your transistor tester gives a readout of the hfe. The replacement transistors should have close to the same hfe,
ideally within 5%. Normally buy the transistors on tape/ammo format, measure the hfe and write it below the tr on the tape, repeat until you have 2 within 5%, also
prefer the higher the better (2 @ 170 rather than 2 @ 150) but not essential.

Prefer not to buy silicon, caps etc from jcar. RS is a better choice, need to register etc...
http://au.rs-online.com/web/
they have them in stock, but they would like to sell you 200. They are commonly used but.

Complete the testing for fried components to get a full inventory. If necessary I can post you up 20xKSA992 if that's all you need, they are like 7cents each???
 
mbz said:
they have them in stock, but they would like to sell you 200. They are commonly used but.

Complete the testing for fried components to get a full inventory. If necessary I can post you up 20xKSA992 if that's all you need, they are like 7cents each???
Click to expand...

Mate you would be a champion! I've tested everything you have suggested so far. The 2 transistors and the resistor are the damaged components. Anything else to check?

Carbon or metal film resistors?
 
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Check the 4x220 ohm resistors 3262, 3266, 3268,3270 and also the trimmer 3264, measure resistance from wiper.
Did you find any shorted transistors? 0-100mV?
 
mbz said:
Check the 4x220 ohm resistors 3262, 3266, 3268,3270 and also the trimmer 3264, measure resistance from wiper.
Did you find any shorted transistors? 0-100mV?
Click to expand...


3262 = DEAD
3266 = GOOD
3268 = GOOD
3270 = GOOD

Most of these read around 208 - 215 Ohms tested on the board
 
trimmer looks ok, if you pm me with your postal details I will send up a envelope with a handful of,
- KSA992
- KSC1815
- KSC1845
- 1N4148
- 47K R
- 220 R
- 10 R (maybe needed for 3298)

average cost is like 5 cents each, total less than a dollar so don't worry about costs,
 
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