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Hitachi HMA-8300 mkII Repair + Restore Help Right Channel Issues

mr.muddles

mr.muddles

Super Member
THIS AMPLIFIER IS THE HITACHI HMA-8500 mk II not the 8300 Sorry for the error in the thread title


Hey everyone,

So I've had this amplifier but haven't had time to look at it until now. When I opened it up the right channel was disconnected... The person I got it from said it was blowing fuses. I powered it on with the right chan unplugged and it passed the dim bulb test and played music through a CD player as the source... Both meters right and left moved on the display???

When I plugged the right channel back in the light bulb went super bright but it did not blow a fuse.

I'm looking for some help troubleshooting this beast. I have a dmm and oscilloscope. I'm new at electronics and self taught.

Thanks everyone!!
 

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The service manual is too large for me to post it says but it is available on HiFi Engine.

I do not see any discolored resistors or burned components to my eyes. There aren't any electrolytic caps I can see aside from the main power filter bank. Outputs are MOSFETS. The guy I purchased from said he had a friend at work who "tested them and they were good".
 
the right channel comes right out there's just some resisters... i don't see a really easy way to pull the resistors and test them out of circuit
 

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mr.muddles said:
i don't see a really easy way to pull the resistors and test them out of circuit
Click to expand...
Unscrew the MOSFET's and unplug them from there sockets on the circuit board . The circuit board should then detach from the heatsink.

Make a note to get the correct FET reinstalled in the right position.
 
thank you. i have tested them in circuit and R609 R610 and the ones just below seem to be acting funny... some of the other ones have drifted too
 
I'm going to test them. I pulled out the other channel and compared the resistor values to the good channel and everything seems to match within reason. i will try and check the outputs now
 
mr.muddles said:
The service manual is too large for me to post it says but it is available on HiFi Engine.
Click to expand...
Doesn't appear to be the correct manual. Look at the output transistors in the schematic. It doesn't show them as MOSFET's
 
avionic said:
Doesn't appear to be the correct manual. Look at the output transistors in the schematic. It doesn't show them as MOSFET's
Click to expand...
The mark II must be way different than the HMA 8300 . The HFE manual/schematic is for a HMA-8300.
 
So I am a dummy, I put down the wrong model number. This is the HMA-8500 mkII

I'm not sure how to update the thread title / subject?

I tried to the best of my ability to test the outputs... all of them match, they all read the same. So I think they might be okay.
 
Can I swap the channels and test them out to see if it will pass the dim bulb? i just want to make sure im not going to fry anything by doing that... by putting the R channel where the good working left channel was I just need to swap where the cables plug in
 
mr.muddles said:
Can I swap the channels and test them out to see if it will pass the dim bulb? i just want to make sure im not going to fry anything by doing that... by putting the R channel where the good working left channel was I just need to swap where the cables plug in
Click to expand...
Might not be a good idea.Besides you have already determined which channel has the problem.The heatsinks are just the final outputs.
 
i thought it might rule out the possibility of faulty components on the two boards attached to the heatsink via the mosfets. if it worked then it would mean that the faulty components were somewhere on the main board?
 
mr.muddles said:
i thought it might rule out the possibility of faulty components on the two boards attached to the heatsink via the mosfets. if it worked then it would mean that the faulty components were somewhere on the main board?
Click to expand...
If the MOSFET's are not shorted then that narrows it down to the main board.
 
Typical TO-3 mosfet pin identification
70-buz900d-2.jpg
 
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Thank you for that video. Earlier I was looking at the schematic and got confused when I saw DGS instead of ECB, etc. I will retest the outputs in a bit now that I know what Drain, Gate, and Source are!

I still think they are okay but will test again after I have some more time.
 
Doing some more testing this morning and it appears as though the outputs are toast after all. So far on the Right channel the pair of 2SJ49 is open between the Drain and Source with about .35 kOhms running across. The K134's on that channel were fine and was able to test good using the test between D,S and the capacitance test. Going to test the other channel for good measure.

I'm assuming there is no chance of getting replacements for these that are suitable?
 
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