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Hitachi HMA-7500 MkII project

393526EB-FBEF-4E50-912E-E5A0A9E7D9EB.jpeg 6BDCFDC5-1351-47F5-BF62-0275F7B4742F.jpeg 8DC16FA3-00A6-47B9-B102-68D51ED1A28E.jpeg 6C1C4BEB-879E-4525-8D64-4DD2C4A87F03.jpeg Hello every one and happy Father’s Day. My hitachi seems to be working now. I swapped between the (exicon) mosfets and the buz mosfets back and forth until the buz mosfets worked. To my eyes they are the exact same thing. Switched it on!!! No short!! Relay clicks.
Connect to the wall.... relay clicks!!! No smoke I’ll be doing some more testing and update you guys Will post pictures also
 
Hello. I had not worked on this amp since father’s day Sunday. Well last night when I plugged it in relay click... everything seems good. But as soon as I plug in the inputs to play some music it goes into protection. And then takes a while for the relay to engage back on. It’s like if it needs to be grounded?
 
tarior said:
You should have all of your connections already made before powering up the amp.
Click to expand...
Thanks @ tarior
I did tried that and I got some sort of sound out of it. And then it went into protection. As far as I had test it. All the voltages check out right. Will continue tonight after work The only caps I have not replaced are the 10uf bipolar caps in the protection circuit. I will replace those once they come in shoul be today according to the tracking Thanks.
 
Have you checked the service manual ? they list checks for the protection circuit, and an 'ASO' circuit ('Area of Safe Operation), which should be done if the outputs are changed.

You also have 2 input options according to the manual - direct coupled,, or cap coupled - is it the problem the same with both ?
 
Goldie99 said:
Have you checked the service manual ? they list checks for the protection circuit, and an 'ASO' circuit ('Area of Safe Operation), which should be done if the outputs are changed.

You also have 2 input options according to the manual - direct coupled,, or cap coupled - is it the problem the same with both ?
Click to expand...
Yes Ok so switch is on. Plug it in to my dbt I have a switch there at the outlet of the dbt... so while the switch on the amp is on I then switch on the dbt. It turns on relay clicks dbt dim. As soon as I touch the power switch on the amp to turn it off and back on it goes into protection. Or last time I plugged in the rca inputs and it did the same.
 
So. I got sound out of both channels. But as long as Soon as I turn up the volume it goes into protection. I tried headphones turning off speaker(A) and (B). And it sounds all good I can turn it up all the way. I thing I’m making progress. At least now I can handle the amp turn it on and off from the switch. Play music. Oh and there’s distortion from the left channel even at low volume.
 
Hello.
Im planing chanching al the caps in my 2 HMA-7500mkII. Do you have complete capacitor list ? The sound very good but i supose they sound even better with new caps and i can play louder :-) The are used as monoblocks.
 
@Leikis
The ceramic caps you can leave in no problem, they do not deteriorate with age.
But for the rest :
There are 4 possible scenarios.

1) the amp is working well, you leave it as is, check the idle current, blow the dust out, enjoy it.
2) the amp is defective, you find the problem and fix the minimum possible.
3) the amp is defective, you FIRST find the problem and fix it, then you go on to a full restoration
4)) the amp is working, but you want the best out of it and you want it to last long, so you give it a full restoration.

There is no in-between, it's no point replacing "some" electrolytic caps.

Your choice :)
 
I did nr 1, so its choice 4 then, or sell them :) I wonder how it would sound with new caps. One of them have sometimes some clicking in the ralays. But its working fine. Like the sound, but its not to mutch power for my Infinity Emim towers
 
<<Ok, these are the relays I'd like to find a drop-in replacement for...anybody ?>>
As of Feb 2023, there are two sellers on Ebay, based in Germany who sell these relays for Hitachi amps. (I have not checked them for a perfect match, YMMV).
 
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