Sansui 9090DB damaged by counterfeit parts!

A large customer of mine went through two techs before sending this 9090DB to me in hopes of getting a faster and cheaper repair. The last two techs used fake parts and improper service techniques so now it's in my shop anyway...and with more damage a bigger bill than if he'd just had it done right the first time!
Worse still, the fault shown could have even caused a fire.
All sorts of parts are being counterfeit these days but few are targeted for fakery quite like discontinued audio power transistors due to their high value and scarcity.
ALWAYS buy from manufacturer authorized distributors and if the original is out of production and is only available from a grey market like eBay or Alibaba, use a modern substitute that you can purchase from an authorized distributor. The vast majority of audio transistors have a modern equivalent that offers equivalent or superior performance so why risk your reputation and the safety of your customers with fakes?
FAMOUS AUTHORIZED DISTRIBUTORS:
www.bdent.com/
www.mouser.com/
www.digikey.com/
www.alliedelec.com/
www.arrow.com/
www.newark.com/
www.avnet.com/
www.futureelectronics.com/
This is a huge problem for the electronics industry as a whole; please see the links below for more information.
"Semiconductor Counterfeiting is a Global Problem"
www.eetimes.com/author.asp?se...
en.wikipedia.org/wiki/Counter...
"Winning the Battle Against Counterfeit Semiconductor - SIA Anti-Counterfeiting Task Force"
www.semiconductors.org/wp-con...
"Counterfeit Semiconductors: The Risk is Real."
• Counterfeit Semiconduc...
"Warning Regarding Counterfeit Goods"
toshiba.semicon-storage.com/u...
"Elliot Sound Products - Counterfeit Semiconductors"
sound-au.com/counterfeit.htm

[@jmgallag]

Nice info! Would love a video on selecting modern replacements, and options when the replacement is in a different package style.

[@MadScientistsLair]

It's in the works but I'm uncertain of when I can get it done. It's gonna be a long video that's going to need to wait for me to get someone with a good camera and a decent whiteboard as well. (I don't think anyone wants a 30+ minute discussion with me holding a selfie stick!) I may however write up something on Reddit on /r/audiorepair in the mean time. (see our index of tips...we have a little treasure trove of links and case studies.)

[@bladzmetube5589]

Great ,, thanks a mill ,, just restored my 2300 from a to z , all solders done ,leds , higher quality caps ,heat sinks ,new wood case e.t.c , This machine is better and nicer than when it was new ,When i went to get my sta-2300 a guy was getting his sansui high end recaped and all , our stereo's were both plugged to the same speaker switch , And everyone there were all surprised that the sta-2300 side by side sounded better with more high and lows , even i was surprised ,at first i didn't want to take the time and do the quality test challenge ,I knew i had something new and good , but didn't want to hear something better than mine on my first day ,,But to my surprised it sounded better ,T'was flattered ..As you said , putting better quality upgraded caps from authorised detailers makes the world of difference ,for a few bucks more ,And thanks to some people like you , We learn and build better machines , And you take the time to explain well , The do's a dont's ..etc ,, Can't thank you enough ... Cheer's..............

[@bradhelms8780]

Thank you taking the time to share your knowledge. I will be honest, I have been tinkering with vintage equipment for a year now. I can solder and use an ohm meter but that is the extent of my experience. I recently purchased a meter to measure mf as I am intrigued with trouble shooting. How accurate will ohm and mf readings be with parts in place on board? I am embarking on a 9090db project where I am having some output issues on right and left channel in A,B or C speaker locations. I have pulled the driver board and tested ohms on fuse resistors. Found the C01@ 656 Ohms and C02 @ 1144 ohms with the spec being at 150 Ohms. Am I heading in the right direction? btw - Do you still have a location in Illinois?

[@MadScientistsLair]

In circuit capacitance measurements are notoriously inaccurate. On something critical like the driver, just replace all the electrolytic caps. In circuit ESR measurements, while still error prone, are more reasonable. Likewise, in circuit resistance measurements are also error prone but the error always skews toward lower than actual value resistance readings. If you're reading higher than spec resistance in circuit, check your connections and remeasure. If the high reading persists, you can be confident that you've found a bad resistor. Note that resistors that have burned have done so because of an overload caused by some other fault. Investigating any transistors or diodes nearby is a good first step to finding why a resistor is burned. As for my location, I'm based in Texas and always have been.

[@bradhelms8780]

@@MadScientistsLair Super helpful... thank you for your post and keep up the good work....

[@stephanebureau5299]

If i replace them with MG21195 and 196, do I have to make adjustments like biasing or change some resistors ? Thanks.

[@MadScientistsLair]

You'll need to perform the bias adjustment procedure as described in the service manual. No component swaps are required.

[@zulumax1]

Have a Sansui G-8700DB receiver someone botched repaired with mix and match transistors on one channel, (SK3836,SK3846,EGC285) also changing a DC offset resistor R08 value on the driver board. The other channel has original red ink Toshiba's with one shorted 2SD551. Driver board has several open, overheated, and high value 1/2 watt resistors including R24 the one that feeds the pre driver transistor TR08. None of the transistors show shorted, but I worry about them having had that much current running through them and being reliable. Also service manual calls out for flame proof resistors, but will the smaller form factor newer metal film resistors be ok to use. They are 1/2 watt, but are the size of 1/8 watt resistors. The 3.9 ceramic power resistor for the slow start is also open. Got the ON semiconductor MJ21194G and MJ21193G output replacements from Mouser ready to go in. When these DC coupled amps go they go big.

[@MadScientistsLair]

The small form factor metal film resistors are OK in this application provided they are rated for at least 200V. They readily go open circuit and do not sustain flame when overloaded. Both driver transistors need to be changed. MJE15035 and MJE15034 work well for the drivers.

[@zulumax1]

@@MadScientistsLair I am assuming those are for the final drivers 2SC2238B(O,Y) and 2SA968B(O,Y) is that correct? Will change out those 330mfd electrolytics while I am in there as well, bring it up slow on a variac and dim bulb and see if she will bias up and balance the DC offset. Thanks for your help.

[@MadScientistsLair]

@@zulumax1 Yes, those MJE transistors are a replacement complementary pair for the final drivers. Don't worry about the lower Ft; the unit will still beat Sansui specs after the swap.

[@MadScientistsLair]

Just noticed that you mentioned that the inrush limiter resistor is open. Check the inrush relay and the timing circuit that controls it. If the relay is OK, you might have a bad cap in the RC timing circuit or a bad relay drive transistor.

[@zulumax1]

@@MadScientistsLair I have already brought it up with a variac and dim bulb with the output transistors pulled. I jumpered in two 8 ohm 20 watt resistors in parallel and the relay clicked on and the tuner and preamp worked. Those are the resistors I use for small powered amps as dummy loads.

[@neonfreon1316]

Great video Andrew, my 990DB has the same broken trace on the PS board. Can I ask how you fixed it? Did you just use a jumper wire?

[@MadScientistsLair]

A carefully placed jumper wire was installed after fixing the underlying fault that blew off the trace in the first place. Repairing the trace without fixing the root cause will result in additional damage.

[@exploringearth3223]

i am restoring a 8080 db sansui i need the output transistors and cant find a replacement can you hook me up with a link ?

[@michaelcottone8307]

I have a 9090Db with -30 volts on both fuses on the relay protection board (DBT in the circuit). If the driver board is out and not on DBT, the relay will click in and zero volts on the fuses. If I am on the DBT, with the driver board out, the relay will not kick in. Changed the diodes, ceramic capacitors, electrolytic capacitors (a while ago), fuse resistors, checked that the output power transistors are not shorted to ground. Went over the solder joints. Check every transistor with an atlas pro transistor tester out of circuit. Any ideas? I am very frustrated! Any help would great.

[@neonfreon1316]

What size bulb are you using in your DBT? I believe it has to be more than 75 watts for the relay to click.

[@MadScientistsLair]

At least. 100-150W is appropriate. With the driver in, it will consume a good deal more power. I suspect the rails aren't coming up due to the lamp being too small or there is actually excessive offset (Check gain matching on the input stage and the offset trimpot.)

[@jerrymarquez710]

Thx for the excellent vids!:) Slightly off topic question… Do you have a vid on TO3 to TO3-P Conversion? Blew up original Sanken finals 2SA747 2SC1116 in my AU 717 I Put in On Semi MJ21193G MJ21194G it sounds fine but just not as fine as i remember so want to go to the faster 2SA1695/2SC4468 in TO3P package to see if i can hear the difference TIA!

[@MadScientistsLair]

I don't but it basically involves bending down the emitter and base leads such that they'll either fit snugly in the socket or far better still, soldering them to pins of the same diameter as the transistor leads, possibly using old TO-3 leads even. The tab of the TO-3 is collector, a simple wire with a ring terminal completes the connection to the collector pin through the mounting screw.

[@jprev]

I just got a 9090DB and the amplifier works great and then the sound distorts after about 30 minutes or so. Don't know much about this as I got one for my dad and now its doing that.. any ideas what that could be?

[@MadScientistsLair]

If it's always about the same time, you may have a thermally intermittent transistor. If you haven't tested and replaced transistors before, this is definitely not a beginner friendly machine and I recommend seeking an experienced technician. LIVE TESTS are required to find this issue and these are inherently hazardous. You can use the pre-out jacks to feed another amplifier. If the audio from the external amp is also distorted, the issue is in the preamp, if it remains clean, the issue is with the power amp.

[@chickenfoundation9323]

Thought on nte components? And where would you buy replacement components?

[@MadScientistsLair]

I try to avoid NTE parts when I can come up with a superior modern substitute on my own but sometimes they are the only game around, especially for ICs.

[@jacobhotaling8959]

lol onsemi makes great equivlents, id not hate fakes so much if they were rebadging genuine parts that were drop in equivilents, but they dont

[@Dylan-cs2vv]

hey man i was hoping you could help me with an issue on my su-g95 i saw your videos about the repair and i myself am having trouble identifying the issue. the unit works sometimes and others it'll say OVERLOAD

[@MadScientistsLair]

Have you removed the mainboard and resoldered all connections on devices mounted to heatsinks and any area of the board darker than the rest due to heat? If not, do that and if you have, double check your work under magnification and strong light. Some of the cracks are as thin as a fine hair. Strong soldering skills are required to complete the repair and high voltage may be present on the main capacitors even after the unit is disconnected.

[@Dylan-cs2vv]

@@MadScientistsLair thanks for the advice, i'll try that and get back to you, is there a safe way to discharge the caps without damaging the solid state components?

[@MadScientistsLair]

@@Dylan-cs2vv If the amp is running at least halfway normally, they should drain to safe levels on their own in 5-15 minutes. Otherwise, connect a resistance of a few k ohms or so across the terminals for a few minutes. When removing the board, handle it with care and avoid contact with traces near the caps, rectifiers and devices on the heatsink as these are connected to the capacitors.

[@Dylan-cs2vv]

@@MadScientistsLair wanted to let you know that after resoldering a bunch of the connections (including both transistors on the heat block, which were hardly on the board at all) it seems to be working. I'll update again if i run into any more trouble. Thanks for the help!

[@Dylan-cs2vv]

@@MadScientistsLair howdy, the new solder seems to have solved the overload issue somewhat. Unfortunately when i turn the input volume or adjust the bass/treble she again overloads. I noted that the fan doesn't actually work, would that be an issue?

[@johnbravo7542]

If your spending $1K to $1,5K on any solid state vintage amp/receiver you're a sucker,even if it has never been opened up and working.People spending that amount of money know nothing about electronics,they believe the hype.

[@MadScientistsLair]

Oh look, another internet edgelord going around like a pigeon and taking a dump on people's hobbies. Hobbies do not need to be rational; they only need to bring the person happiness. People like their old stereos, they want them rebuilt, and I provide the services that make them happy. I spend money on "stupid" stuff too. I have my own crazy stereos and let's not even get into the time and money I've put into project cars or how much I've spent restoring historical computers. Those cars and old computers are not exactly wise investments but I have no issues affording them. They make me happy and I enjoy the hobbyist community around them. Everyone with any amount of discretionary income will have some hobby that others just don't see the point of. I can't see myself spending thousands on MTG card decks or golfing equipment but I know people that have and they get their money's worth of enjoyment out it.

[@Texan1048]

Is it necessary to match the output transistors?

[@MadScientistsLair]

Transistors within the same gain rank will do in a pinch but I recommend hand matching if you can.

[@Texan1048]

@@MadScientistsLair oh boy so I'm gonna need a shit load of MJs then

[@MadScientistsLair]

@@Texan1048 10 of each will generally get you a decently matched set ot two. I generally try to keep them hfe matched to within 5%. The outliers can be used for non-paralleled output stages.

[@MadScientistsLair]

@@Texan1048 Remember to measure with all the transistors at the same temp. Even handling them while measuring will skew the results because hfe varies with temperature.

[@truthfinder6996]

is it possible that these transistors are ordered and made recently and are originals. And to save on cost they had to follow 21 century cheap standards

[@MadScientistsLair]

No. These parts have been out of production for nearly 40 years.

[@truthfinder6996]

@@MadScientistsLair thanx for replying, I recently bought NEC B536 and NEC D381 drivers for my sansui G6000 from an electronics shop which have old stocks of transistors and one is also different from my Sansui old one in terms of color. BTW can you help me and suggest a replacement transistors for old 2SA981 and 2SC2261 ones, if yes, also tell if I have to change drivers (mentioned above). along with the replacement which you may suggest. plz here in our town it's only me and good people like you who will help me fix my sansui G6000.

[@razegs]

fusisor?

[@MadScientistsLair]

Its shorthand for "fusible resistor". It's a resistor used as a fuse. The ones Sansui used tend to fail over time even if they aren't overloaded.