Hitachi SR-2000L Repair

The SR-2000 is one of the most difficult amplifiers to repair because if you had to replace the hybrid amplifier module you would need access to the underside of the main board, and that requires taking the whole unit apart. I took the back plate and front panel off, and there was still the slight matter of the tuning string, which also requires undoing.

This amplifier required a replacement STK463 hybrid module and I managed to source a cheap one from a Chinese seller on eBay. However, from experience, I know that these modules can sometimes be faulty and even fakes. Whilst the sellers are quick to say sorry and produce a refund, it does not make up for the lost time of having to take the amplifier apart again. Therefore, I decided to install a chip socket in place so that the module could be easily removed without having to disassemble again. This modification also gave me the opportunity to try other equivalent and compatible hybrid modules that were available cheaply.

Diagnosis is of course very simple, because the thing to remember is that these old amplifiers do not have a speaker protection relay that isolates the speakers in the event of a short circuit in the hybrid module. Hence, a faulty hybrid module can feed large voltages to the speakers and damage it. Therefore, the clever thing to do is to first connect a digital meter to measure the voltage the speaker terminals are producing. In this case, there was +11 V in one channel and -22 V in another. Connecting a scrap speaker to the channel that had +11 V produced sound but it was very distorted. At this point, it was obvious that another hybrid amplifier module would be required and I decided to go on-line to see if one could be found cheaply.

I am glad I installed the chip socket because the first hybrid module that came all the way from China turned out to be faulty! I was getting -15 V DC from one channel and +20 V DC from another, and only one channel produced a distorted sound, whilst the other was completely dead. That is a shame I thought as the replacement module was very nicely packed in anti-static bag and they nearly made a believer out of me! I unplugged the module, wiped the heatsink compound from the surfaces, and decided to go online again.

I managed to repair the original hybrid module by reconnecting the wire that had burnt and broken off and it works. However, this is only a temporary fix until I can find a working module.

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