2220B - yet another tuner issue

Alrighty, then...... A pair of HA1156 chips are on the way. Stay tuned, and wish me luck. I'm very close to putting a few rounds through this POS, just to ease my pain. :)
 
The replacement HA1156's arrived yesterday, and I installed one today. Pin 6 remains at or near 10v, and Pin 8 is fluctuating between 0.0v and 0.08v TP J208 remains constant at 0.61v, even when sweeping the mute trimmer and R304.

>SIGH<...... I guess the good news is that I now have spare HA1156 chips. Any other ideas? I'm dying here..................
 
So, I replaced the temporary 150 Ohm resistor I had at R311 with a 100 Ohm one, as shown in the schematic. Loyal readers might recall that there was a 10 Ohm resistor there to begin with. The lamp lights, but is very dim.... I'm thinking 10 Ohms might be the correct value as it came from the factory.No joy - still no stereo lock, Pin 8 still near 0v. Grounding Pin 6 gets me a light, but that is not a solution. :(

How the hell can I get the voltage up on Pin 8? Anybody? Anybody at all? I'm dying here...................... check that, I'm dead unless someone has a fresh idea.
 
catrafter said:
I'm still reading...
It's hard to decipher what has or hasn't been tested.
I only have the schematic from a non-Dolby 2220B so take the references with a grain of salt.
When the signal strength is high enough for stereo operation H209 will turn and it's collector and J209 will go to nearly zero volts. This 'ground' at J209 is sent though a bunch of switch contacts to J308, which should turn OFF H303. With H303 OFF, HA1156 pin 8 should rise to about 3V enabling it to decode stereo if it finds the proper pilot signal.
You can safely ground pin 6 to see if the lamp comes on, this will only tell you if the path from pin 6 through the mono switches, the lamp and the lamp power source are OK.
PM sent on HA1156 source.
Click to expand...

Tom,

The base of H209 is at 0v, the Collector at 7.17v. and the Emitter at 0v. J209 is at 13.75v. J208 is at 0.62v. Does that tell you anything useful?
 
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When the IF signal strength is high enough, H209 B should be above 0.6V and it's collector should go to near 0V, ditto for J209.
Your H209 readings say that the signal strength is not sufficient for stereo operation or that the tuner front end (P100) or the IF amp (P200) is defective.
What is puzzling is that J208 and J314 SHOULD follow H209 C and J209, but at a lower level, ie, if H209 C is at 7V, the J208 should be at some positive voltage as well.

Tom
 
catrafter said:
When the IF signal strength is high enough, H209 B should be above 0.6V and it's collector should go to near 0V, ditto for J209.
Your H209 readings say that the signal strength is not sufficient for stereo operation or that the tuner front end (P100) or the IF amp (P200) is defective.
What is puzzling is that J208 and J314 SHOULD follow H209 C and J209, but at a lower level, ie, if H209 C is at 7V, the J208 should be at some positive voltage as well.

Tom
Click to expand...

Interesting. The signal seems good, reception is loud and clear on many stations. Also - the music sounds pretty good to me, but I guess it is still mono? Dunno.What's left..... shotgun the transistors on P100 maybe? Change out the little electrolytics on P100 and see if that helps?
 
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Since FM station(s) come in clear, I would wonder if the circuit consisting of H206 and it's associated parts are working.
A small sample of the IF is sent to H206 where it is amplified and applied to two rectifiers (H217 and 218) to produce a positive DC voltage proportional to the signal strength. This DC voltage is used to ultimately turn on H209, turn OFF H303 to enable stereo operation of the HA1156. H302 should be OFF (collector at about 3 volts) in FM, it's purpose is to kill the FM VCO to prevent interference in AM. You can safely test FM operation with H302 removed.

Tom
 
I'll chime in here, take it for what it's worth. Anytime I have a tuner that won't tune in stereo I make a determination as to where the issue lies. For starters, you need to test to see if the MPX board is indeed functioning. Once upon a time I made informed decisions to replace MPX IC's only to find out that I was wrong in my assumptions. I always have a spare working receiver or tuner on deck that I can pull IF signals from to see if the MPX is indeed working. What you can do is take a signal from a working receiver, from the IF and inject it into the MPX board of the questionable unit. This will determine if the issue lies in the MPX circuit or before it. I've done it countless times- due to the fact that FM is so difficult to troubleshoot doing these simple things can narrow down where the issue lies. On simple tuners this works- you can also inject the signal from a front end into an IF board to see if the issue is in the front end or the IF. Once you determine where the issue is you can start pulling components and testing them. Lately I've seen a lot of "gain issues" with transistors in units- I fixed a 2275 2 days ago with a defective meter transistor, I pulled it and found it had a gain of "4". Once replaced the meter started working again as well as the tuner as a whole. It had an effect on where stereo was being pulled in- you wouldn't think it would but it did. I'm willing to bet your seeing a similar issue, gain has dropped off the map on one of the transistors in the IF.
 
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