2325 FM Right Channel Distortion

[Perkinsman]

Both channels work fine on all functions except for FM. However, on FM, the left channel sounds fine and I’m getting stereo separation but the right channel is very weak & distorted. All the transistor/IC voltages on the P300 board are very close to the schematic. I’ve removed the necessary boards to access & deox all pots & switches. What else should I be looking at?

 

[sanjib]

I cannot remember whether right channel has an odd or even-numbered component. Anyway, check C323 or C324, H304, H306 or H305, H307. Do you have a scope? Someone better in troubleshooting tuner might help you out here.

 

[sanjib]

To properly trace the quality of signals in both channels you need FM signal generator which can send the 1KHz modulated signals and you can check the quality of signals at pin 4 (left channel) and 5 (right channel) of H321. If the signal is distorted there, the chip is bad or if you have the nice equal signals at both pin 4 and 5 you have to check the capacitors and transistors I mentioned in the above post. The right channel has the odd-numbered components.

 

[sanjib]

I totally forgot that 2325 has a 400Hz test tone switch in front! You can switch on the testone and if you have a scope you can check everything as I stated above. If you don't have the scope you can check the ac voltages in the above-mentioned points with your DMM.

 

[Perkinsman]

Thanks Sanjib, I'll definitely check those out first thing in the morning... I only have a working dmm for now. Do most schematics list the AC voltages? If not, is a scope the only way to "see" a distortion problem?

 

[sanjib]

Measurment of AC voltage is for tracing the signal if you don't have scope. Schematic voltages are DC. If you see equal ac voltages at pin 4 and 5 that means H312 is working properly and then check the ac at both sides of C323 and on the base and emitters of of the transistors I mentioned to find where you losing the signal. If you see a big difference in AC voltages between pin 4 and 5 of H312 most probaly it is bad and in that case measure DC voltages at those pins and compare with schematic to make sure the IC is getting proper power.

 

[Perkinsman]

Did you mean pins 4&5 on H321? If so, both approximately match on ac (70mvac) & dc (9.8vdc).

I had replaced c323 with a wima already & both legs measure approx 25mvac.

H305base=24mvac, 1.29mvdc
H305emitter=.5mvac, 1.12mvdc
H307base=jumpy vac, 20.2vdc
H307emitter=jumpy vac, 19.5vdc

Did I miss anything here?

 

[sanjib]

Your H321 is good. Check both ends of both C323 and C324 if they are good you will get almost equal voltages there, then check the H305 base and compare it with the H304 base (that I guess working one). If identical result, check the emitter and collector of H305 and compare it with H304. If you get all identical readings then check at the collector of H307 and compare it with H306 if they are identical move to C326 (both legs) compare with C325 (both legs)

 

[sanjib]

We are trying to find where the signal gets distorted and I hopping if the signal gets distorted it will reflect in a different AC voltage (unstable, jumpy) than the undistorted one. With a scope, it would have been much easier to see the distortion.

 

[Perkinsman]

All voltages are vdc
C323 legs=1.27 & 9.87
C324 legs=1.28 & 9.78
H304 b=1.27 c=20.14 e=.728
H305 b=1.28 c=20.12 e=1.11
H306 c=11.87
H307 c= 19.3
C325 legs= 0 & 0
C326 legs=19.38 & 0

Do you see any problems with these measurements?

 

[sanjib]

Check AC, not DC. Please read my above post #9

 

[sanjib]

In one channel (I am guessing left and is working in your case) you have to check C323, H304, H306, C325, and in another channel (I am guessing right and is distorted in your case) you have to check C324, H305, H307, C326 and you have to compare both channels to find where the distortion appears by checking AC voltage. I think you will find a jumpy, unstable AC voltage in case of a distorted signal.

 

[sanjib]

Looking into your DC readings, if you have 11.87 dc at the collector of H306 you should have 11.87 dc at one leg of c325, not zero. If you have zero check the solder joint of c325 and also the trace going to the collector h306 from + leg of c325. DC voltage at the collector of h307 is high it should be like h306

 

[Perkinsman]

Here’s the approx AC readings:
C323=25mv each leg
C324=24.5mv each leg
H304 b=26mv c=1.5mv e=26mv
H305 b=26mv c=.4mv* e=.1mv*
H306 b=1.6mv c=416mv e=.4mv
H307 b=all jumpy*
C325=427 each leg
C326=1.7 each leg jumpy
If the Left Channel (even numbers) readings are correct, then I put an * next to each significantly different reading on the Right Channel (odd numbers). So do you think I should replace H305, H307? Any others?

 

[sanjib]

It looks like H305 and 307 are not working properly. Replace H305 with KSC1815 and H307 with ksa992 and check.

 

[sanjib]

To be sure you can first swap H304 and H305 and check whether the problem swaps the channel or not. Two possibilities: left is distorted and right is fine then the problem is only H305, both channel distorted then both H305 and H307 are faulty. If both channels are distorted then swap both the problem should swap channel if our diagnosis is correct.

 

[Perkinsman]

Ok, thanks, I do have some 992’s but I’ll need to order some ksc1815’s, I only have ksc1845’s.

So the approach you took was to compare each channel components in the signal path on the P300? Knowing the L channel was working well, if any of the R channel showed significantly different readings, that would make them suspect, correct?

 

[sanjib]

Yes, you are absolutely right! If you have ksc945 or KSC1845 you can try it for now. For KSC945 make sure it is KSC945C version with the collector at the center.

 

[Perkinsman]

Yep, the 1845 is ECB! This board has so many pins to remove, I think I’ll wait until the morning when I’m fresh.....Thanks Sanjib, I’ll touch base tomorrow after I try it out, you’ve been so helpful.

 

[catrafter]

I use face stands made using screws, nuts and fender washers. I can then fold the P300 board down to get to the solder side. I do the P150 AM board the same way. You may have to remove somew wires fron th plastic looms that hold them to the chassis.

Tom