Technics su-v3

gpounce32768

Active Member
I found a nice "parts or repair" su-v3 on ebay, the plan is to put it upstairs for the TV speakers- no need to waste my nice jvc mca-v7e quad doing that. The seller says one channel is not working, case is a beat up a little bit, one of the switches is binding, price was right... perfect! :)



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Its certainly a basic design. I really like the much-reduced harness complexity- we'll see how it sounds.
 
Nah going to fix it.. else why bother lol. Looks like somebody has been in before me; cut jumpers on the board near the inputs and flying leads soldered on, leading to the front panel. I've not done a powerup yet, I have to get the front panel off and test the power transistors.
 
Both channels OK- the problem was some previous tech had removed the cable between the vol/eq board output and amp input, then cut the jumpers bringing #1 tape loop playback/record signals into the system. Using flying leads seen in the pics, the record-output was wired to the volume/eq output, and the playback-input wired to the amp input. So the effect was the implementation of a pre-out, amp-in pair via the #1 tape loop jacks, and all #1 loop functions inoperative. Without the pair of pre-out/amp-in cables connectors in the jacks, no signal to the amp. I replaced the cut jumpers and rewired the vol/eq to amp input signals; amp is now working fine, also having done the controls with de-oxit.

Going to go for the idle current adjust and power measurement- the balance adjust pot is completely dead, looks like somebody put it in w/o a nut on the backside of the panel to hold clearance with repect to its position as soldered to the board. So when the panel nut was tightened the pot was torn apart internally.
 
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Wow, a Technics with actual transistors.
Trying to be sarcastic? Sorry mate, but the majority of Technics amps were built with separate transistors in the output stage, as opposed to chips. This was especially true in the 70s and 80s.
 
Found a 50k linear taper pot at Radio Shack, not a perfect fit but good enough. I cut the stem and put a flat on it to take the knob, then fit it up- amp is good now but theres some lurking contact issues that I'm slowly getting straightened out. Its a pretty basic amp but sounds fine, perfect for the idiot box- time to swap it for the v7e which I want to mess around with a bit more.
 
The amp easily makes 40 watts clean, rails are stiff & quiet. idle currents were off quite a bit, and the vu meter adjustments were off a lot. All dialed in now. The schematic shows 100k pot for balance, 50k works fine- as long as its linear taper. Time to install it on the tv and move on to fixing an oscilloscope...
 
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