Hitachi HMA-8300

[bosedtobosed]

got a 8300 thats has blown one channel, a fuse and 2 of the T03 transistors a 2SA1117 and a 2SC2608, i believe this is a class G amp the circuit\layout looks unusual, with 3 big smoothing caps, one a double for the low voltage +\-37v and 2 for the +\-90v supplies, i was going to replace all the T03 transistors with MJ15024\25s, there is quite a bit of info on the web about this amp most of it assuming it uses mosfets which it doesnt,

 

[Netlist]

According to the manual, the original output transistors are 2SD675/76 and 2SB655/56.
The rail voltages are +/-39 and +/- 95V.
There are probably some bad solderings in the driver board that need checking together with blown fuse resistors.
If you don't have the manual, I'll try to scan it.

/Hugo

 

[bosedtobosed]

thanks i would appreciate a manual, those transistors are on the lh heatsink there are 2 2sd676s on the other with 2 others i cant read the nos off (a mix and match), there were a few bad solder joints but generally its in good condition, i believe the board gets damaged from heat around the low power heatsinks, i am guessing the 2 presets are the bias Iq adjustments, ive checked some of the fusable resistors and they seen ok, might have to dissasemble further, the brown bits at the corners are repairs to the mounting positions.

 

[bosedtobosed]

R10L is o\c in series with a diode, looks like it should be 100ohm the one in the other channel measures 230ohms, and are similar to the fuseable resistors used in sansui 717s that change value !

 

[Netlist]

YGM.

 

[poetry2me]

Hi,

I just restaured a badly mis-repaired HMA-8300. All fuse resistors should be replaced.
The second differential stage transistors Q703, Q704, Q705 suffer from extreme heat due to high quiescent current through that stage. Lots of diodes dead. Power transistors all replaced with 2ST2121 and 2ST5949.
I posted everything here: http://www.hifi-forum.de/index.php?action=browseT&forum_id=185&thread=7185

- Poetry2me