Technics Turntable 1982 SL 7 problems after recap - no power

[Somerville]

Hi, Im needing some help after a recap Ive recently completed on the Technics SL7. When I purchased it everything worked and functioned correctly.
After doing some research on this model it was common to have very leaky capacitors due to age.

So I had a peak at the pcb and it showed many capacitors with green corrosion on legs.

Work completed -

• All electrolytic caps replaced with exact same MF though sometimes replaced with higher voltage rating
• re flowed a few solder joints
• De oxit all switches and plugs

I have gone back through all of the work I did and confirmed the correct polarity of caps and looked for potential solder bridges. (all looks good)
All connectors are plugged in properly

I noticed a cracked solder on the IC1 (voltage reference) after re flowing join still no power. Is it possible that this has caused damage somewhere else when powering up?

I tried plugging in the 12v outlet also and still no power

Any ideas on where to start with this issue?

 

[rayma]

What do you mean by "no power" ?

What are the DC voltage outputs of IC1 (+12V) and IC2 (+5V) ?

 

[Somerville]

Sorry, when I press the power switch on the turntable the lights are off and no functions work. Ive measured the voltage of IC1/2 and they are not reading correct voltage

 

[rayma]

And what are the output DC voltages of IC1 and IC2?

And what are the input DC voltages of IC1 and IC2?

 

[Somerville]

Tested so far - (12v supply)

IC1-
1- 29v
2-12v
3-12v
IC2-
1-12v
2-0
3-12v

Q201
C- 12v
E- 0v
B- 12v

IC101 TP8 (15) - 12v

Q203
C- 12v
E-0v
B-12v

Rectifier - 12v

 

[rayma]

Please make this more clear, and distinguish between the dashes and the minus signs.
Use an equals sign instead of a dash.

Also go back over your work, and check each capacitor for proper polarity and good solder joints.
Check nearby areas on the pcb for solder splashes, etc.

 

[mikey_audiogeek]

According to the schematic you showed, the DC supply requires centre pin negative (earth). Most 12VDC power supplies have centre pin positive.
There is no reverse polarity protection inside the SL-7.

Cheers, Mike

 

[ManoloMos]

"When I purchased it everything worked and functioned correctly."

I don't understand this fashion of replacing capacitors without any reason.

Yes, it is true, Matsushita Capacitors sometimes have leaky, ESR or low capacity problems. Sometimes it is noted by rust in their legs. But, if it works, don't touch it.

 

[Mark Tillotson]

"Green corrosion" on "many cap's" leads is a very solid reason indeed - it suggests the entire board was built with bad caps (see badcaps.net). The correct response is replace all electrolytics if you suspect this to be the case, no questions asked.

 

[ManoloMos]

Green rust on Matsushita Capacitors are present only in tiny sizes and some values only, not all matsushita capacitors suffers green rust.
Green rust is not a big problem, if you measure the capacitor, I'm almost sure that ESR and capacity are in correct values.

 

[Netlist]

IC 1 should have:
Pin1 = 18V
Pin2 = 11.8V
Pin3 = 0V

IC 2 should have:
Pin1 = 11.8V
Pin2 = 5V
Pin3 = 0V

Did you measure with respect to ground (Pin3 on both IC's)?

Hugo

 

[Drummerboy2]

Hi, Im needing some help after a recap Ive recently completed on the Technics SL7. When I purchased it everything worked and functioned correctly.
After doing some research on this model it was common to have very leaky capacitors due to age.

So I had a peak at the pcb and it showed many capacitors with green corrosion on legs.

Work completed -

• All electrolytic caps replaced with exact same MF though sometimes replaced with higher voltage rating
• re flowed a few solder joints
• De oxit all switches and plugs

I have gone back through all of the work I did and confirmed the correct polarity of caps and looked for potential solder bridges. (all looks good)
All connectors are plugged in properly

I noticed a cracked solder on the IC1 (voltage reference) after re flowing join still no power. Is it possible that this has caused damage somewhere else when powering up?

I tried plugging in the 12v outlet also and still no power

Any ideas on where to start with this issue?

Always do a few parts at a time, this way if something goes wrong you what area or parts caused it. If change out a bunch of parts this what happens, you don't where the issue is at.

Go over all the capacitors your replace with a magnifying glass to see if there is any cracked or open traces. also make sure all caps are in correct polarity.

You know the old saying, if it ain't broke, don't fix it.