No protection light, no output. 9090db

ejg3855

Member
Cliff notes: I started rebuilding the F2624 driver board as this was the obvious root cause of my protection light, many hours/dollars later I never got a working unit (I assume something is wrong with the traces on the board) I sourced another board from a user on AK and plugged it in and the unit worked great for about a year.

So where I am at now, about 2 months ago while listening to the FM tuner I would notice a channel drop out If I switched the unit to dolby FM on the dolby knob it would get back to stereo mode. I lived with this and didn't do much research onto the root cause as I know the Dolby piece on this is notorious for problems, apparently all the audio is routed through the dolby board whether or not its being used.

Tonight I was again listening to FM radio and heard 3 pops, not super loud and the unit went into protection. I powered down the unit gave it a few mins, tried it again to the same result. I can get the unit to turn on and not go into protection, but I notice some oddities. The FM tuner needles will not move the balance one is stuck perfectly in the middle. The output RMS needles will bounce like its trying to power the speakers and the protection is green but there is no power to the speakers.

I will try and set/check the bias and dc offset over the weekend. But other than that I am at a loss. Any help our guidance would be great.
 
The dead tuner tells you that the +56V rail is likely out and possible/probable cause is R30 fuse resistor on the power supply board has failed high/open. The fact that the power meters are showing indication suggests that the outputs are not blown. However the pops you heard are worrisome. Are the speakers of a significantly lower power rating that the receiver? They could have blown during the transients caused by the power supply failure. The speaker protection relay contacts may also have taken a hit and be burnt/dirty. Look for burn marks on the inside of the perspex relay cover..
 
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I agree with Doug with the recommendation of verify ALL the supplies PLUS make a DBT ( or use it if you have one ) to keep the imported expensive smoke to escape!
 
You may have multiple issues. The tuner has it's own power supply, board F2619. It's prone to failure due to heat. It also powers the Dolby board. Check it for bad solder joints. Also be sure the shaft hasn't backed out of the Dolby switch. If so, one or more of the switch wafers may not be turning. Look at the back of the switch. You will be able to see it if its out of place.

When the tuner power supply fails, it typically won't trip protection but will give you the symptom of a green protection light and no sound output. You wont get sound output from any source because the Dolby board looses it's power too.

- Pete
 
Guys, I haven't had a chance to check these things out. But Thank you a ton, I will hopefully get to them tomorrow. The knowledge on these boards is amazing.
 
The dead tuner tells you that the +56V rail is likely out and possible/probable cause is R30 fuse resistor on the power supply board has failed high/open. The fact that the power meters are showing indication suggests that the outputs are not blown. However the pops you heard are worrisome. Are the speakers of a significantly lower power rating that the receiver? They could have blown during the transients caused by the power supply failure. The speaker protection relay contacts may also have taken a hit and be burnt/dirty. Look for burn marks on the inside of the perspex relay cover..

I do have a DBT and will make sure I use that also, the speakers are rated for 150 or 200w I cannot recally, i just remember its over the power capability of the unit.
 
R30/R31 were blown

Do I need to replace them with "fuseable" resistors or can I use generic 1ohm resistors?
 
most folk are moving away from fusibles because of their reliability/availability issues. The consensus seems to be to use non-flammable or flameproof; available from mouser and digikey. There are S&H costs far in excess of the device cost so you may wish to investigate further to see whatever else you may need before ordering..

If it were my unit I'd use a metal film resistor of the same power rating for testing and replace it later...
 
I got some replacements, unit is back up and working. The channel drop seems to have gone away also so that's cool. I deoxited all the switches a few times.

Do you believe the root cause is just older failing components ? Or should I be digging deeper for a root cause?

sent from the beige bra section at target......
 
There are S&H costs far in excess of the device cost so you may wish to investigate further to see whatever else you may need before ordering..

As an option, DigiKey will ship for free if you send then a check. When I need a few small items, that's what I do. It has only taken maybe 2 days for them to receive my order and get it out in the mail - not a big deal to me. They are great about that.

http://www.digikey.com/Web Export/Info/order-form-terms-us.pdf
 
Don't sweat those resistors failing. In later production 9090DBs, Sansui replaced them with fuses. The combination of the age of the resistor and a power surge can pop them.

- Pete
 
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