Repair of Crest VS1100 Amplifier - Tour Class
Fault - Dead
On initial inspection when switched on nothing was happening except the cooling fan started up.
Removed the top cover to reveal the inside - nothing looked to be blown in fact this was one of the cleanest Crest amplifiers we have ever seen.
Unfortunately the access to these amplifiers is limited and the only way to find out what was going on was to strip the amplifier down
Transformer and fan removed
Main board, heatsink/booster board out on the bench with back cover still attached.
After solving the initial fault - the amplifier being totally dead, which we won't reveal, the amplifier was rebuilt and appeared to work correctly, however whilst testing it became apparent that we had a huge 85 mV DC offset on channel 1, the amplifier was stripped down again and serious bit of testing had to be carried out, we found all the output transistors OK, driver transistors OK, we checked pretty much everything in site that could have caused the problem.
Now sorry to explode the myth of VS range of Crest amplifiers but these models have a Sanyo STK3152 integrated amplifier chip on the front end - yes just like the one in your $20 Hi Fi ! all Crest have done is built the amplifier around this Sanyo Chip, which they forget to mention in their glossy brochures, I would feel a bit cheated if I had brought one of these, thinking it must be top of the range American design only to find out it was basically created from the application sheet of the cheap Japanese Sanyo STK3152
Anyway I am starting to waffle, back to the job in hand, because this chip controls both channels of the amplifier including the offset voltage it was a racing certainty that this was the problem, so we fitted a new chip
See the new chip fitted below
These devices are a pig to remove even with our de-soldering station and extreme care must be taken with removal.
After fitting the chip we re- built the amplifier and re- tested - the offset voltage on both channels was spot on about 12 mV
All in all this amplifier is not bad, it is what it is, despite my opinion on the use of the Sanyo device, the unit is well made, has a good solid transformer 14 output transistors per channel and would seem to be very reliable which is the main thing, far better than most Chinese built amplifiers available today
Front view showing power on, ready for shipping back to the customer
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