Advent 300 - What Am I Looking At Here?

[rmoreau61]

Several years ago I got two Advent 300 receivers that aren't working (the price was right). Here I am several years later finally pulling them out to have a look see. I recall one of them was a fuse blower, but I don't remember which or any other details. At the time I thought maybe I would get one working unit out of two.

So, I opened up the units and "one of these things is not like the other." The main filter caps are completely different from each other. I checked around for some schematics and repair experiences others have had. I learned there's an older version and newer version but schematics don't support what I'm seeing.

I understand this product was aggressively designed to be cost competitive, but this cap configuration doesn't even seem to meet the standards of the wiring rats nest and jumpered parts soldered in.

What am I looking at here? Why would one unit match the documented 3000 uF pair of caps while the other unit have twin 6800 uF caps (along with other parts hanging on - a bridge rectifier circuit?).

 

[sregor]

I believe you are over thinking it. The 3000uf caps frequently get broken leads, and someone replaced them with higher capacitance parts. Pretty common practice... my 2 cents

 

[rmoreau61]

Thanks for the quick response!

On the contrary. I've given it virtually no thought at all. I pulled the covers, looked around and saw caps at more than double the value in one unit. I only went as far as to look at a few schematics all calling for 3k uF caps. For other power supplies, I've seen filter caps replaced with values up to maybe 50% higher in value. I didn't know if this was a model 300 variant I hadn't seen docs on or a mod that might be out there that accomplishes something in particular.

From what you're suggesting, maybe somebody just pulled some parts that were handy to get the unit to work or something (although I don't expect to get a heartbeat when I get around to checking it).

 

[cademan]

Both might be factory stock but one might be a revision.

If one is blowing fuses, I would be looking at a possible shorted diode or output transistor and not worry about the difference in capacitors. Higher capacitance would probably just give more oomph in the bass department and less sag in the power supply.

Do you know how to check for shorts? Level of expertise?

 

[rmoreau61]

I would rate myself an idiot savant. I can check for shorts, check voltages when I find them on a schematic, follow signals, but I have no real idea what the components do or why.

 

[cademan]

Aw don't call yourself an idiot. You're way above that as you are here to learn.

 

[Robisme]

Looks like somebody replaced the caps and the rectifier. Maybe the diodes are rated higher than the original rectifier.

Rob

 

[Lavane]

Looks like somebody replaced the caps and the rectifier. Maybe the diodes are rated higher than the original rectifier.

Rob

That was my first thought. If they are replacement caps and diodes, at leased there was some thought about the rectifier upping the cap values that high.

 

[rmoreau61]

That was my first thought. If they are replacement caps and diodes, at leased there was some thought about the rectifier upping the cap values that high.

Agreed. I feel a lot better about the mods done based on this info.

On a separate note, I've pulled a Crazy Ivan and started checking voltages on the receiver with the 3000 uF caps. Replaced a blown fuse with no replacement blown. C401 is reading -21.6V but should be -15V. Then my wife woke up... She pulled a crazy Ivan on my priorities.....

 

[larryderouin]

As long as she gets more aggregate time per week than the gear, you should be ok. But always remember, when SWMBO ain't Happy, everyone else within 500 yards is miserable! (SWMBO=She who must be Obeyed!) Peace offerings usually help (shoes, purses, a day at the spa, kitchen appliances,etc........................). Stay away from sharp objects as peace offerings tho. Scissors and Large kitchen knives are dangerous, and can be considered an impediment to your prolonged health. Just be warned that this hobby can get REALLY EXPENSIVE, FAST! And you haven't bought parts yet.

 

[Stuart Pedaso]

I checked around for some schematics and repair experiences others have had. I learned there's an older version and newer version but schematics don't support what I'm seeing.

Advent 300 schematic is pasted to the bottom of each unit from the factory. If yours have survived, they should reflect any revisions in the unit they're attached to.

 

[rmoreau61]

As long as she gets more aggregate time per week than the gear, you should be ok. But always remember, when SWMBO ain't Happy, everyone else within 500 yards is miserable! (SWMBO=She who must be Obeyed!) Peace offerings usually help (shoes, purses, a day at the spa, kitchen appliances,etc........................). Stay away from sharp objects as peace offerings tho. Scissors and Large kitchen knives are dangerous, and can be considered an impediment to your prolonged health. Just be warned that this hobby can get REALLY EXPENSIVE, FAST! And you haven't bought parts yet.

I've survived 36 years with no visible scars! My only remaining fear is she enjoys falling asleep to the Investigation Discovery channel. Not sure what she may learn there...

Advent 300 schematic is pasted to the bottom of each unit from the factory. If yours have survived, they should reflect any revisions in the unit they're attached to.

Sadly, no schematic under either unit.

 

[larryderouin]

I've survived 36 years with no visible scars! My only remaining fear is she enjoys falling asleep to the Investigation Discovery channel. Not sure what she may learn there....

Sleep learning, . 50 ways to......................______________ (fill in the blanks).

Late wife threw cast iron Fry pans with a mean side arm. Make Sandy Koufax proud. But she couldn't get it in the strike zone!

 

[rmoreau61]

I checked a couple more voltages and wasn't seeing anything outrageous. I forgot to mention, the FM tuning light had come on as well. I decided to look around a bit more to get a sense of how the unit is doing. I may have found a possible source for fuse blowing. A transistor by the 4A fuse looks to have been replaced but the leads on the bottom of the board were never trimmed. I removed the bottom cover before doing any voltage checks and those leads are long enough to have shorted against the cover. I also noted the wires to one of the tuning Leads were clipped. Lastly, the volume shaft is out too far. I can only think I pulled it out when I removed the knob so now it's free wheeling. I decided to connect some speakers since it appeared to be behaving. Long story short, FM sound with no antenna (unusual for the valley I'm in). Right channel very loud so I flipped the balance to the left and was able to adjust the volume. All things considered, it sounds good with all knobs and switches functioning (volume problematic of course).

That's all I've got time for today. Kind of shocked it works, but I'll trim those transistor leadsforvsure.

 

[rmoreau61]

Removed the volume pot, dismantled, reassembled with a good dose of deoxit. Tested and resistance looked good (after having one channel 180 deg out). Installed, reassembled and turned it on. Works! So now it's on to checking other functions and then replacing parts to get it up to spec. Sorry I didn't take pictures of the volume pot. I didn't think of it as an exciting exercise. Bottom line, it had to come apart to get the shaft back in position.

 

[rmoreau61]

Peeling back the onion. Treble not working in right channel. Not working. FM tuning lights, low LED always on and high LED always off. Many functions still need checking. FWIW, when I pulled the RCA plugs out of the jacks, they were filled with dust fuzz....