/diy/ - Do It Yourself

>>573934

Well, somehow its working perfectly again... I asked some folks at audiokarma, and they said check R72 which is variable resistor for the stereo sensitivity. i was getting 115ohms when it shouldve been 350.
and at that point I found one lone trace that was lacking solder and I guess that made it work. I feel like an idiot.
Thanks for all your help man, for real

>>573882
I understand that the switch makes contact with 2 at a time, either the top and middle, or the bottom and middle, which turns it on of off. I get that. What I don't get is why there are THREE sets of contacts for the FM, for example, The schematic lists only only one. (picture, (left side)
Bear with me here, I'm trying to learn as fast as I can!

the cap was C60, located in the MPX area (picture, right side). but like you determined earlier, the MPX was bypassed completely, and it still didn't have an effect.

>>573617

I am looking at the schematic and the switch leads, but honestly i have no idea how to test it..

the ONLY cap that was backwards was a 2.2uF, really tiny guy. I lucked out on that.

I'm still trying everything I can but I'm running out of time

>>573545
Here is a picture of the switch mechanism, where do I put the leads to check it?

>>573549
Well, when I first got the unit I replaced all the electr. capacitors, which is why I'm rechecking them, I replaced about 20 or so, so I want to make sure I didnt foolishly put one in backwards

>>573491

Good suggestion. I have found one so far C60 (which is within the MPX circuit). in my defense, the - side wasn't clearly defined on the board. HOWEVER. I am still getting dropouts so I will look for more.

>>573481

yes, I checked power sources as per >>573200
I put deoxit in S201 ( which is one big slidey switch) as per >>573174
i checked Q1 initially and got conductance in fwd direction but not reverse as per >>572664
I will continue to look for cold solder joints

worst case, I live without FM radio on this thing. AM works, Tape In/out works, Phono works, speaker works...

bump for advice

>>573200

Also since you've come this far, here is a link to the full service manual.. https://www.mediafire.com/?kcf1zrgubvas1ou

>>573174
I checked all voltages from 1-5 (power) and 6-7 (FM) and got ranges +/- 1v.

>>573181

Right right, sorry. I'll do the Ohms testing.
And I didn't replace them, just removed them to test and put them back in. I have equivalent transistors on hand. 2N2222 are proper replacements for the ones in the unit (GE part number GE-20), so that's fine.

>>573174

Some transistors that I removed and checked had low hFe values, they read 151 instead of 200 (for a 2N2222). Is this an issue?

i'll check the voltages and S201 and I'll let you know

>>573171

The tuning meter, as in a little needle dial that goes up when a station is a stronger signal and goes down when there's no signal. And it doesnt work at all on FM mode, stereo or mono, but works fine on AM mode

>>572999

Ok, I bypassed the MPX by going from C59+ to C66 (out) but I'm still getting the dropouts...

>>572971

Thanks for the help, but as >>572998 said, it probably won't help in my situation

>>572999
I'm just going to buy some new transistors while I'm at it, and get some more desoldering braid at radioshack.
I'll give the bypass a shot when I get back from the store.
Yes, both the station will come in and the stereo light will glow and then both will fade out simultaneously..

>>572861
Well I know I dont have an o-scope.. but what kind of amplifier thing would I need?

>>572863

I desoldered one end of each transistor to test it (bringing it out of circuit). By desoldering/resoldering with amateur skills, I think I either messed up the trace around the hole or just did a crappy resolder job.
I started at Transistor 1 (Q1) and worked my way down the list, so I desoldered at least one lead on most of the FM transistors. I didnt touch any of the other alighnment settings,

OP here,

so I fixed that one, but I'm still getting drop outs.
basically FM stations come in and fade out instantly and the signal intensity needle doesnt even register on FM, but works fine on AM.

I attached the schematic. the entire upper row is FM circuitry. the intensity dial is M3 which is upper 2/3 right area (look for the big arrow and follow it down.

due to the size I cant post the full thing, but it's here: http://i.imgur.com/xKKcsFs.png

>>572805

yeah. i lost my soldering gun actually. i found it about 5 minutes ago, but I now I can;t find my desoldering braid...

>>572687

i've learned that the hard way, on other projects. I currently use braid, but i think I'll get something similar to what you show. seems like it will do the trick better.

I think i found the bad solder joint. Im going to resolder it here soon

>>572673
Sorry, gun was just the term I was using, but I actally use whats in the picture. It hasn't let me down let, and its only 30W.

I'm going to visual check each transistor solder spot and see how it looks. I'll let you know in a few mins.

>>572664

Thank you for that, I replace the caps when I first got it, so that's all good. and dont worry about the age, I visit AudioKarma pretty often so it's all good man.

The more I look at the solder joints, the more I think that I need to get my gun out.
Now what happens when the little metal 'O' that surround the hole in the board comes off? I'm pretty sure the solder contacts that which sends it to the circuit...

Secondly, there are voltages at each end of the transistor in my original picture, how do I test those?

>>572661

It's a 70's console unit. A while back I was trying to fix (what ending up being) a blown power transistor for the L channel. I systematically went Transistor to transitor looking for the bad one, starting with Q1 (transistors are marked Q1,Q2 etc, on this set). I eventally found the bad transistor, but I screwed up the FM amp ones in the process. What's happenig now, is that any FM station will come in loud for 2 seconds then fade out instantly, then resume after 30 seconds or so, and repeat. I KNOW that didnt happen before I messed with the transistors, so I'm pretty sure I just didnt solder one back to the board correctly.

So, tl;dr I want to check the FM amp transistors to make sure they're making contact with the circuit.

a few years ago I worked on this, and I'm going back to it again, except i've completely forgotten, how do i test voltages thru a transistor in a circuit?

pic related.

OP here.

In the short term its probably better for me just to spend 5$ to replace the cap instead of trying to test it. the speakers belong to a R2R I got, and honestly if the caps are bad the unit has it own internal speakers that I can use for now.

>>565366

those are nice but idk if it's worth it to spend 100$ to fix a speaker set I got for free.