• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

2250 Has Developed A Smoking Habit... help.

Sounds like you found the problem, R808. If the Zener was shorted, it would connect it to ground.
If zener was shorted R808 would be connected to ground and power thru R808 would be:
P = V^2 / R = (44)^2 / 3300 = 0.6W. R808 is a 1/4W = 0.25W resistor, but the voltage there looks good. You didn't change any electrolytic caps and by chance put them in backwards by mistake, did you?
R806 is a variable resistor. It should read 5k ohms across the outer two leads. The center lead is the tap, or wiper and will vary with rotation.
 
Last edited:
I have not done any changeouts- yet.
I am ordering all of the electrolyts (Nichi) for that board as I type this, along with another 3.3K resistor

dankik said:
R806 is a variable resistor. It should read 5k ohms across the outer two leads. The center lead is the tap, or wiper and will vary with rotation.
Click to expand...
What exactly is that trimmer controlling, where, and what should the voltage at that place be?



You all have been great. So a failed R808 IS the problem, or is it a symptom of something else?
 
Resistors rarely burn up on their own. Excess current through a resistor is usually caused by a fault in another component; but, you've narrowed it down to very few culprits. (1 transistor, 2 diodes, 3 resistors, and 1 capacitor.)

I would replace the suspect 330uF cap (I'd do that whole board while you're in there) and the bad resistor. Set the regulated voltage to 35v and see if it behaves.
 
Last edited:
Make sure the zener diode is good -- at least acting like a diode. I've had more than one or two short and blow things up over the years, especially in hot running locations (as in the whole board on my KA-80). Only way to tell if it's actually running at the correct zener voltage is to build a test circuit or check when powered on.

Open in both directions or shorted, replace it.

You can check the transistor using the "diode test method" -- any two of the legs will read as a diode junction using the diode test setting on your DMM. Should read OL in one direction and some voltage drop between 0.2 and 0.9V the other depending on circuit and type. Won't tell you if it actually works as a transistor, but at least open both directions or shorted is bad and it needs to be replaced.
 
Thank you @HPMguy

I will report back on results after parts arrive in a few days. Hopefully they come soon enough to allow me to set and see before my total replacement knee surgery a week from tomorrow.
 
Ugh, knee replacements are rough. Do ALL the exercises they prescribe before and take a pain pill if you have to for the PT after, if you don't get full range quickly it can be a problem!

I hope your surgery goes very well.
 
The wrap on some of those power board caps has shrunk because the caps got pretty hot. When I see that, I at least test the caps. Power board is workin’ all the time and those caps are probably pretty tired.
 
Creeping shrink wrap is pretty much diagnostic for high ESR and excessive heat, usually leakage and climbing capacitance as well on a Chinese tester. I would replace them all.
 
Thanks @rBuckner and @HPMguy on the surgery. Looking forward to it. Really.

I understand why I cannot put an LED bulb in the STEREO beacon- it can fry the IC that controls it.
But can the AM light use an LED? Most kits only sell 5 and that is one shy of all indicators (sans STEREO).
 
You can use an LED there if it either has a built in current limiting resistor or if one is added in series with a plain standard LED. The ones rated for a certain voltage should have a resistor in line internally. They're usually too bright though but an additional resistor can be added to tone it down.
 
Can’t you just use the correct 12v incandescent bi-pin for the stereo light? I have a light kit on eBay that’s complete and only uses LEDs for the fuse lamps.
 
EastPoint said:
Can’t you just use the correct 12v incandescent bi-pin for the stereo light? I have a light kit on eBay that’s complete and only uses LEDs for the fuse lamps.
Click to expand...
I was not asking about changing the STEREO beacon- that is a new incan now from the kit I bought.
I have already installed the 5 input indicator leds but there are six to replace (not including the Dolby light), so one has the old incan still in it (AM).

So L-R, it is
(old incan)...(old incan)...(LED)...(LED)...(LED)...(LED)...(LED)...(new incan)

I ordered another warm white led for that now, so all input function bulbs match.
(old incan)...(LED)...(LED)...(LED)...(LED)...(LED)...(LED)...(new incan)

I did not go with original replacements because I want crisper lighting. However, I am carefully filtering dial and indicators to match the original (what I call) Mediterranean blue hues.
 
Ah, I see. You can use LEDs for the source lights, they just don’t look great in my opinion. Too bright.
 
Alright- the caps and resistor for the PS board are here from Digi-Key now. In the next 3 days-
I will be working on that,
re-stringing the tuner (I broke the original by trying to route it after having messed it up 4 months ago,
- QUESTION: should the varicap fins be fully nested together for dial pointer being fully left?
Or, would you recommend tuning a known station, then placing the pointer on the string?
installing the final LED source lamp (yet to arrive) and finalizing the dial and source intensity and color filtering to get close to original,
checking the three recommended voltages yet again before closing it up,
finishing the wood veneering of the original top/sides panel

Then- again- replacement knee on Weds.


I am anxious to see this all play out- it was a $30 GW purchase in 2013.
 
Last edited:
You have it right; the fins are fully meshed at the left end of the dial (88MHz). Before putting the dial pointer on, I would make sure that the loop and hook connection point doesn't run afoul of either end's pullies. Then put it in place, no glue yet, and make sure the end to end travel has it going as far off to the left end of the dial as the right. That centers it mechanically. You could then dial in a known high end station and move the pointer a little if that's all it takes. then see how the left end lines up. It's easier to adjust the low freq. oscillator slug than the small variable cap trimmer. Often those get stuck with dust and dirt and moisture and getting them loose can loosen the mechanism and change the capacitance, almost always making them not adjust enough.

The dial pointer, when put on, will take a bit of slack out of the string. So if the string seems to slip at first, putting the pointer on may help it enough. Restring the dial cord is a PITA, just keep after it!
 
Thanks for the tip, @rBuckner


Now... frustration. I replaced ALL electrolyts and the fried R808 (with a 2W)- and something is STILL smoking.

H810= 14.2v
H809= 7.2v
Regulated voltage J804/5= 35v
R808. Left=14.1v R=19.6v, rel to gnd.

Next play? I am a little frustrated and greatly disappointed.
@dankik @willyrover @HPMguy
 
You must log in or register to reply here.
Back
Top Bottom