Dead QRX 6001?

[Reed]

I am about 95% done recapping my first Sansui QRX 6001. All has ben going well. This unit was an eBay purchase for $81 and has never worked since I got it a few years ago.

Anyway, I had to order more caps from Mouser, so i decided to put it back together enough to check if I am getting any sound yet.

I plugged in some headphones, attached an external antenna, turned the volume all the way down, plugged it in, and turned it on. No smoke or fire, no explosions. No sound either in any channel, front or back. I tried it in AM, FM, and auxiliary modes, 2 channel, and every four channel mode. If I turn the volume all the way up, I can faintly hear the music, but that is the only way I get any sound. In FM and AM mode, I hear nothing and the signal meters don't move throughout the entire range.

In four channel mode, none of the indicator lights work, but I know the bulbs are good (I checked them). The 2/4 channel blue and yellow indicator lights also do not light up.

No fuses are blown on F-2427.

I checked voltages at pins 13 and 6 on both F-2436 boards and the voltage was low (33.8-34 volts instead of 37) but present.

Is my unit dead? Would the low voltage keep the unit from coming out of protection mode? Are the decoder chips toast?What do I do next?

I don't want to give up on this unit just yet. I have replaced just about 90% of all the capacitors on all the boards. Thanks.

 

[Reed]

Anyone? Bueller? Bueller?

At this rate I may cut my loses and just focus on repairing my other 6001 that has front and back sound on the left channels only and appears to work in all quad modes. Maybe I will take the best of both 6001 units and combine them to make one functional unit.

 

[Doug G.]

The first thing to do is check to see if all volatges are available from the power supply. I am not familiar with the Sansuis but that is standard procedure for any unit not functioning 100%.

Do you have troubleshooting/repair documentation so you can see what these voltages are supposed to be?

Doug

 

[Reed]

I have the factory service manual but it only talks about checking the voltages pins 13 and 6 on both F-2436 boards. LIke i said, I have voltage there, but it is 2-3 volts lower than specified. I will keep researching and probing around.

 

[krkier]

I have the factory service manual but it only talks about checking the voltages pins 13 and 6 on both F-2436 boards. LIke i said, I have voltage there, but it is 2-3 volts lower than specified. I will keep researching and probing around.

Isn't page 30 of the service manual showing voltages of the power supply unit?



And do all other schematics give you no a hint about voltages within the different functional groups?



-Kristian

 

[Reed]

Whoops! I was only looking at the troubleshooting section, not at the schematics. My apologies. I am not a professional or even trained electronics technician, just a hobbyist who had a couple electronics classes in high school many years ago. I will go back over the schematics and check for voltages and then probe the PCBs and verify those voltages.

Thanks for pointing out the obvious that I was missing.

 

[Reed]

OK- the voltages from the power transformer to board F-2456 all check out to within four volts of spec. However, I discovered that fuse 7 on board F-2427 keeps blowing. Fuse 7 on board F-2427 feeds power transistor TR 707.

So it looks like my next step is to order up a new set of power transistors. I might as well replace them all if I know one has failed.

The game continues. Thanks for the reminder to read the f'ing manual!

 

[quadsearcher]

Just a little friendly advice. Just replace the pair in the channel that blows and save the rest in case the new ones blow. Check the rest of the chain before the shorted output---the driver, pre driver (s) and all associated resistors. There is a way to run the rest of the circuit without the outputs to test for DC offset and avoid blowing the new ones, but myself, I find it better to check all the drive transistors before them as well as the resistors.

I hope I don't sound too preachy, it's just that I had a lot of disappointment 30 years ago when I started repairing as a hobby and then was much happier when I learned a better way. With a scope, a variac with current meter, ohmmeter with megohm scale to check reverse leakage (or curve tracer), etc.

All that said, I'd try TR707 and its compliment first, having spares in case. The other channels' outputs might be fine. This doesn't explain no sound from the other channels unless it is protection, which I haven't looked at.
Have you checked all DC supply outputs from board F-2427?

 

[Reed]

Preach away! I know nearly nothing about what I am doing, so I appreciate all the input.

I have not checked all the outputs from F-2427. Once I get the blowing fuse fixed, I will move along to checking the outputs. I have also been checking for obvious faults such as blown or melted components.

As far as tools, right now I have a soldering iron and a DVOM. I would love to have and know how to use such things as an oscilloscope, but that has to wait until later.

I appreciate the help greatly.

 

[krkier]

As far as tools, right now I have a soldering iron and a DVOM. I would love to have and know how to use such things as an oscilloscope, but that has to wait until later.

That's like repairing a car with just one screwdriver...

-Kristian

 

[Reed]

That's like repairing a car with just one screwdriver...

-Kristian

Hey, been there, done that. I am actually a fairly competent auto mechanic, so I do appreciate having the right tools for the job. However, until this point I just haven't had the need for any electrical tools more sophisticated than a VOM. That may change though.

 

[Doug G.]

When you say power transistor TR707, do you mean output transistor? In other words, one of the transistors which drive the speakers?

If that's the case, I would remove that transistor and see if the fuse still blows (or, in other words, is there still too much current draw). If the fuse doesn't blow, it means that that transistor is probably shorted. I would test it too. Actually, I would test it before firing up the unit.

In most cases, the output transistors blow from a user not heeding load limitations on solid state components. Usually, the transistors before the outputs are still good (there are exceptions, of course).

Doug

 

[Reed]

I believe it is one of the transistors that drive the speakers. The schematic identifies it as "TR707." It is one of the transistors attached to the big heat sinks on the back of the unit. I am testing this unit with no load on it. No speakers, not even headphones yet, but since it was an eBay purchase I don't know the user history.

I will have to research how to test a transistor and see if I can do that.

It does appear that a drink was spilled into this unit as some point in its life. There is a large amount of sticky lint on the metal chassis and a white residue on the bottom of a couple PCBs. That might also be the cause of the short.

 

[Reed]

Well a bit of excitement and disappointment tonight. I got done recapping the first 6001 and replacing a few resistors I found that had fried. I replaced the blown fuses, plugged it in, and turned it on. Right out of the gate fuse number 3 blew, and the the capacitor on the board that hooks to fuse number three actually exploded. I got excited because it was done, then depressed because it was all for naught. I am admitting that I am over my head with this project and will be packing the two QRX-6001s away in y storage next to my half-dead Pioneer QX 949A. I did buy a Pioneer QX 747 on eBay that is supposed to be fully working, so it will have to hold me over until I can afford to pay someone who knows what they are doing to fix my Sansuis.

Thanks for the tips and encouragement, but this stuff is just beyond me.

 

[w.a.reid]

you did better than i ever did - and at least you burned ...only yourself with the trial/error repairs. good try and you still have a couple of qrx machines to ebay if you get tired of looking at them.

im going to try qrxrestore on a qsd1 and then a qrx7001 - because i know that im not as good as you are with this stuff...and look at where you ended up.

w.a.reid

 

[Reed]

It gets worse. I actully sent this unit out to a supposed QRX specialist who charged me $500 (plus the $80 shipping each way) and didn't fix anything. Sure, I see he installed some new caps, but the unit still doesn't function. He blamed me for hooking the unit up to bad speakers when I got the unit back, but I tested the speakers and they were fine.

i still have these two QRX-6001s in my storage unit, one recapped with an extra $500 of balancing and news caps done to it, waiting for a day when I have more time or money or just get sik of them and want to sell. I keep getting burned and I think I have finally learned to not trust anybody.

 

[w.a.reid]

It gets worse. I actully sent this unit out to a supposed QRX specialist who charged me $500 (plus the $80 shipping each way) and didn't fix anything. Sure, I see he installed some new caps, but the unit still doesn't function. He blamed me for hooking the unit up to bad speakers when I got the unit back, but I tested the speakers and they were fine.

i still have these two QRX-6001s in my storage unit, one recapped with an extra $500 of balancing and news caps done to it, waiting for a day when I have more time or money or just get sik of them and want to sell. I keep getting burned and I think I have finally learned to not trust anybody.

well - dont be shy - oust the dude....i might have something headed his way.

if you dont want to its ok - but im going to. this happens way too much. so much so that paypal has gotten in on the act - they actually have a payment process that lets you pay a tech....wait for the machine....and when you get it - or dont - then you can open a paypal claim to get your money back from said tech.

paying a tech with paypal is one thing.....but ppal always had a 45 day return policy. but it often takes more time than that to get the machine back from tech...so you could not open a claim of not receiving item....or did not get what was advertised....i.e. - a repaired piece of gear.

now, that has changed a little - techs have nothing to fear if they are honest. if they decide not to give you gear back...thats hard...but you will get money back. if you get your machine back and its still broken - open a ppal claim...and start process to get your money back - its pretty quick.

this is all hindsight i know....but we all are still moving forward.

give us a repeat of what went wrong after the tech burned you and naturally placed blame in your lap.

bad speakers? can anyone validate that a bad speaker burns a receiver?

c. ready in PA said that all the problems that i was getting in the mail from him were my fault because "i must have made some enemies at fedex and they see my packages coming and damage them"
im fucking serious - thats the type of bs you get when youre dealing with someone 20 hour drive away.

rehash it if you can - let others weigh in - if you got dealt bullshit from a tech...then help us all out - who? what? where?

bad press is still good press....only in hollywood.

w.a.r.

 

[quadsearcher]

A shorted voice coil in a speaker, or one tiny strand of wire even briefly shorting one terminal to the other while on will blow most amps instantly. If one channel's outputs go, protection usually keeps all speakers off.
Generalities and not specific to Sansui. Far more often though, the voice coil will open, not short. An open speaker does no damage to transistor amps.

Certainly not suggesting this is what happened, Reed, just a reply to the above question.

-john.

 

[Reed]

Agreed and understood John. In my case, though, I tested the speakers and they were not damaged or malfunctioning in any way. I just got burned, again.

 

[dr8track]

well - dont be shy - oust the dude....i might have something headed his way.

if you dont want to its ok - but im going to. this happens way too much.

I agree that you would be doing many people here a service by revealing who did this work for you. It's really no different than submitting a rating on something like Yelp. It just really helps people make up their minds about whether or not they are confident enough to take their business to this particular person. It's quite possible that he has many satisfied customers as well, but the fact that your experience was unsatisfactory would be helpful for someone to know if they were considering shipping a unit off for repair.