This Arvin 8576 only had low background hiss & light crackling on speaker/headphones, zero tuning/receiving. Volume of hiss does go up and down with volume control which I didn't clean yet so I can hear the scratchiness too. Recap only increased volume of the hiss somewhat but not a whole lot. I noted voltages that were way off from what is on the schems, or which are not on the schems and I was not sure if they are okay, and doubled up on numbers that might be a little fuzzy.

Schem and board diagram don't indicate which 2n94 is which but I verified the one that reads funny goes to T3 so it's the second one. I don't know if I have one bad transistor, or two, or? Also I verified my new caps but found C16 polarity as replaced did not match the schems so I reversed it. Maybe I just goofed (likely!) or it's a schematic error but either way I didn't note any change in the sound or in the 2n35 & 2n270 readings so maybe that's something to revisit if I get the radio going again. Do the schems look right on that one?

What would be a good place to start, find a 2n212 replacement? Does it look like could be some other issue(s), or something else I can measure or do first that might help diagnose it better? Thanks... Mark

An ECG103A would be a good replacement for the 2n212 which definitely seems to be shorted CE. With regard to the 2N94, I might check R7, R8 and R9 before declaring the 2N94 bad. It could be leaky and cause that mis-bias and may indeed have to be replaced. And ECG103A will work for that as well (unfortunately about $4.50 each). You could also swap the two 2n94 transistors (lot of extra work) and verify the problem follows the one that appears to have issues.

Curtis Eickerman

Okay I'll start with pulling the 2n212. I do have some *supposed* equivalents for that one - 2n1302, 2n1304 and 2n35 (depending on which old transistor equivalency book I downloaded that I look it up in, or what sites on the internet say) that I'll try before buying any. I also have an old 2n94 and maybe a couple others that might work that may be good. If the resistors check out I will pull the 2n94 and test on my meter.

R7/8/9 checked out okay so I pulled the 2n94 and it is definitely toast - fails the two diode tests that should read '1' and won't give me an HFe reading on my meter, just a '1' like out of bounds. The 212 reads '12' HFe but passed the four diode tests so not sure if it's good or bad or weak. Thought I had a 2n94 but I don't so I've ordered a couple of 103As for $3 each, will see how it goes.

Many of the early transistor types have very low gain.

Yeah since it tests 'good' in diode tests and I do get a valid gain reading, seems like I'd get something more than absolute zeros with it in the circuit unless it's a different issue.

A little progress... The replacement for the 2n94 resulted in E= .35 and B= .45 so that is close to the schematics now instead of crazy high. But the 2n212 replacement still reads about 0.1 on the base and zero E and C. So seems like maybe the old 212 might be okay after all and the problem is elsewhere(?) I checked the diode out of circuit just to make sure it was okay and it is. I get continuity between the antenna wire going to one of the screws on the tuner and either of the other two ant. wires going to the board, but that's with all the wires in circuit. No noticeable change in sound with the new transistors, same low hiss and varying light crackling and they go up/down with vol control, and no reception whatsoever. If I bring my LED worklamp near it which would normally would cause a huge racket, I get no effect. Anything else I can measure, or disconnect and then measure someplace?

It is probably time to check resistance from collector to B+ with the battery removed (should be near 8.5k). Also check emitter to ground (should be near 1.5k).

Curtis Eickerman

Measured these on the 2n212 with battery removed but volume switch 'on':
Collector to B+ = reads as shorted, no resistance
Emitter to ground = only 550 ohms, not 1.5K
So sumptin' not right there.

And in case it's of any use, while I was at it: E to B+ = 1K... C to gnd = 550 ohm
In circuit: R3 = 1.4 K, R21 = 22 ohm, they look ok.

Also on the tuning cap, with its frame as ground and tuner fins fully separated, I get continuity to the moving fins, no continuity on top stationary fins, but continuity on the bottom stationary fins. That last one ain't right is it?

I can pull that transistor out again if would help make add'l resistance checks easier/more useful.

And don't know if I'm doing this right, I've never checked coils in any of my radios before so far.
Going by the schematic diagram and assuming it is the bottom view like the transistors are depicted, on A4 I measure:
Pins 1 & 6 - continuity
2 & 4 - continuity
2 & 3 - no continuity
All the exposed wires up top seem intact. But if this was the problem I dunno why I'd be reading that continuity on collector to B+ unless that is another problem, so I probably don't know what I'm doing with this part, just poking around.

The 6-1 continuity on the oscillator coil is good. The 2-3 lack of continuity is not good, but will wait (it will affect the ability to oscillate but has no affect on power to the collector). Next you should check the continuity on the 1-2 connection of that IF transformer that is on the far right of your partial schematic. If that is open you wont have any power to the collector. Basically follow the connection all the way back to the B+ terminal of the battery connector.Note: To check resistance to the battery terminal, the battery will have to be disconnected but the ON-OFF switch would have to be in the ON position.

Curtis Eickerman

I got continuity starting from B+ up to R4, on other end of R4 (8.2K) I got 1.5K. Stayed 1.5K from R4 to A3 pins 1 & 2 (and also pin 3), and on to A4 pins 1 & 6 (the collector.)
So I was wondering why only 1.5K on the other end of R4, so I yank one lead. Checked out at 8K across it. Soldered the lead back in and all these readings have now dropped to only 500 ohms? Why would I go from B+ continuity on one end of R4 to 1.5K on the other end in the first place if the resistor really is 8.2K? Is R4 just plain messed up? I don't understand this at all.

***Update - Okay I think it has to do with the polarity of my ohmeter leads, if I switch them around during this test the ohms switch between 500 and 1500. Is that supposed to happen and what is the correct polarity for my test leads?
So maybe the emitter to gnd reading is actually okay at 1.5K if I switch the test leads around, but I know I was getting continuity between collector and B+ before, whereas now I get resistance but I didn't change anything between these two different tests except testing R4 alone after the tests. And it's still not 8.2K. Redid the V tests and the 212 repl. still reads the same 0/.1/0.

I will admit your readings are not making much sense at the moment to me either. Can you do a resistance check from Collector to Emitter on the 212 both ways with your meter? Everything still seems to be pointing to a short between the Collector and Emitter whether it is the device or a short on the circuit board.

You might want to remove the 2N212 then put the battery back in place and turn the radio ON. Then measure the voltages on the CE and B connections where the 2N212 was attached.

Curtis Eickerman

Collector to emitter resistance is the same deal as the other measurements, 550 ohms, or if I switch the test leads around then it's 1.5K. Just not seeing a short there even with the transistor installed, but it ain't 8K either.

Pulled transistor:
Voltage - Base went up to 0.7, C and E zero.
Resistances - B+ to collector, same thing, 550 ohm or 1500K depending on probe polarity,
C to E = 1.6 K, either direction

I checked A3 a little more, the only continuity is between pins 2 to 4. 3 to 2 and 3 to 4, nothing. Got continuity between pin 3 on the board trace and a bare spot on its wire where it comes out thru the wax so I'm guessing the coil is open within the windings. If it is, oh well, after about two dozen transistor radios I fixed so far, first time for everything. Only things I had to deal with before this were recaps, and a rare bad transistor or ceramic cap once or twice

Try looking at a cold solder joints by probing the transformer leads on the board (Bottom side)

>>Try looking at a cold solder joints by probing the transformer leads on the board (Bottom side)<<

I tried reflowing all five joints on A3, no dice.

Have you checked to see if C4 or C5 are not shorted? If either are shorted, this could explain 0 volts at C and E of the 2N212. I have seen shorted low-voltage disc ceramic caps in transistor radios the past.

Dave

I pulled one lead each from C4 and C5, not testing as shorted. With them out of circuit, if I measure across either of their respective solder points I do get full continuity. And that's with the transistor still pulled out. Is that significant? Looks weird. How are the disconnected cap points reading short across them if only one point goes to ground and I don't even have the transistor in there?
--Update-- so after seeing this... checked all four points of the disconnected C4 and C5 board points, all four read continuity to ground. And pin 6 & 1 of A4 do as well. Could that be an additional problem in the A4 windings besides the open connection between point 3 and points 2 and 4?

I guess the next step would be to remove the IF transformer (T-1). Then you can see which side of the coil the short is on, or if the coil, itself, is shorted to the can. At least we know now that there is a short somewhere.

Dave

Might as well, that A4 is beginning to look like it's headed for the radio parts graveyard.