Technics su-v85a amplifier

[jgray59]

I have a Technics SU-V85A. A friend plugged an mp3 player into the Aux 1 input and the amp popped and went into protection mode. I couldn't get it to recover. I found the schematics and started doing some checking. My probe slipped and I shorted a cap. and a resister. In trying to replace them I tried a 1/4 watt 22 Ohm resister and it fried. I have a problem with the resistor at R477 on the schematic for the Voltage control Amp. circuit. it says it is a 22 Ohm resistor but no clue as to weather it is a 1/4 watt or a 1/2 watt. I have tried 1/4 watt and it fried and popped the cap at C463. Anyone have any idea? I really loved the sound of this amp and would love to get it working again!

Here is the manual. https://www.hifiengine.com/hfe_downloads/index.php?technics/technics_su-v85a_service.pdf

 

[SVI2004A]

Check Q401 and Q402 on front pcb (runs from IC401)

It's possible that c463 failed taking out R477 and upon replacement died aswell.

Check for shorts in the transistors on the V amp section

The resistor most likely is a fusible - will gave to check in my manual when I am near it

 

[jgray59]

Check Q401 and Q402 on front pcb (runs from IC401)

It's possible that c463 failed taking out R477 and upon replacement died aswell.

Check for shorts in the transistors on the V amp section

The resistor most likely is a fusible - will gave to check in my manual when I am near it

I had to remove the board from the face To get to the V Amp section. Following the circuit to Q401/402 I found R409 and R410 were burnt. I need to order these parts and install before I can continue. Thanks for the direction.

 

[tonyk]

I just wanted to say I've owned a couple of these su-V85a Integrateds, they are wonderful sounding units and well worth the time spent on repair.

Good luck.

 

[ZOOM]

I wouldn't bother with the repair. It usuallly ends poorly on these Technics units. Especially if you aren't a pro.

 

[ryuuoh]

Mileage does vary depending on the driver.

 

[jgray59]

I've replaced C463, R477, R409 and R410. C463 still wants to fail. I need to check to see if there is something burnt that I haven't seen. Not seeing anything that looks burnt and If I power it up it pops C463. Any ideas that I might have missed?

 

[jdsalinger]

Can anyone describe how to disconnect the flat harness of the tone control board from the main board? Technics has a different type of connector on EVERY harness it seems.
Some pull right out, some have snap on retainers. I took the retainer off, but it is really hard to pull up on the connector.....I don't want to break it.

Troubleshooting an issue where I get highly variable output from both channels. Goes from bass distortion, to very quiet, to no sound, then back again. Happens in both channels too.
Bypassing the tone controls (button) seems to improve things a bit, but it is still touchy. I have adjusted the voltage and current per the service manual.
I have not deoxited the controls or switches yet because it seems like a failed component to me.

I'm thinking some tone board transistor.....or could it be caps?

 

[grabread]

Avoid powering on until you have fixed the fault. you will do more and more damage. Probably one of the amplifier output ic's have fried and until properly diagnosed and repaired things will pop and burn each time you power on. Forget looking for burnt components, many fail but look ok.

 

[jdsalinger]

OK, I figured out that the connectors are mounted on the main amplifier board. The harness is a flat ribbon type that has stripped leads which insert into the connector and are held in place by spring retainers. You have to use a flat screwdriver to push down on the retainers inside the connector to release the ribbon.

Unfortunately, I found part of my distortion problem. The treble pot threaded shaft was broken off from the pot case, so the slider probably wasn't even making contact.

The bass, treble and balance pot all appear to be full of grease. I don't think I want to de-oxit those. I'll deoxit the switches only.

 

[grabread]

I have this amplifier. It's the push buttons that are a big cause of problems with this unit. spray deoxit in to them and push the button in/out maybe 100 times, do this for all of them

 

[ScottFan355]

I recently acquired this amp. I'm wondering what people's impressions are of it's gain. To me it sounds wonderful at up to fairly loud volume, then a bit hard, and then clips hard and fast after that. With a line-level (cd) input it started clipping at about 11 o'clock. This worries me a bit as my tweeters are virtually unobtanium,

 

[jdsalinger]

I have this amplifier. It's the push buttons that are a big cause of problems with this unit. spray deoxit in to them and push the button in/out maybe 100 times, do this for all of them

Thanks for the advice grabread. I did what you said. Took another listen and it started off with stability issues on the right channel (had been left) but then settled down. I bypassed the tone controls and listened to 2 hrs on my Advent 5012's with no distortion tonight.

This is my first Technics and now I'm a fan. Sounds as good or better than my tube gear. Last SS amp I had was the legendary B&K ST-140 and I regret selling it, but this Technics amp is more exciting and musical. The SU-V85a has SUCH great separation and dynamics. The B&K was extremely detailed and quiet, but with the Technics, I'm enjoying favorite songs for the first time again.

I put some JB weld on the broken treble pot shaft (and the bass and balance for good measure). No chance in finding replacements, so I have to repair what I have.
This amp is DEFINITELY worth the effort. I just hope I can get it reliable again.

 

[jdsalinger]

I may do that, but could you elaborate on your suggestion? I have read a lot of comments about how Technics don't like to be worked on and should be thrown away if a problem arises. Is this the consensus or just one guy who did the shotgun approach?
I have read of amps dying after a recap, but how do we know the aptitude of the person who recapped?

I am pretty confident at my ability to replace components. I don't have a technician's test equipment though.
I bought this fairly cheaply. It is not in good cosmetic shape and thus, I never intended on sticking a lot of money into it or taking it to a service center.

At this time, I am simply doing a thourough de-oxit treatment and a visual assesment (which turned up the broken pot shaft).
Sometimes these issues tend to go away with some use. Not always, but sometimes.

I am also aware of the output modules being very dangerous if close to failure, but this amp has discrete output transistors. Should I be concerned about those too?

( by the way, I hope it's OK to post my journey in this thread.....I just thought that because the title was so general and the fact that the thread has been dormant for a year, it would be appropriate to post in this thread ).

 

[jdsalinger]

So far, so good. After repairing the treble pot, there was no distortion tonight, even with the tone controls "in".
Maybe just a slight brief instability for the first 10 seconds, but after that, I was able to mess with the knobs and switches with no problems.

OK, now I'm lusting for my next Technics. Maybe a power amp.

 

[grabread]

I like Technics amps I have 3 in my collection. I find no particular problem in working on them. Difficult to find the stk output ic's now and reproductions can be good but also can be bad.

 

[SVI2004A]

Aren’t aware of any counterfeit SVI ICs yet... think they’re a tad niche for the counterfeiters

But you do have to be weary of STKs out there *kicks the Chinese rip off crowd*