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SX 450 No AM/FM

larryderouin said:
Pin 20 on the RF Assy bd is the main B+ for the tuner. Check for 13.7Vdc there. Follow it downstream to
a.) H1156 Pin4, Pin 5 (Both 11.2v), Pin 1(13.7V)
b.) Q105 & 106 Emitters (no voltage given) These are 2sa725's known troublemakers. replace with KSA992's.
c.) Selector (S3) Wafer 2 Front pin 2 (13.7V). With Selector in AM Check pin 3 for same voltage, then Pin 2 HA1137 (1.9V). In FM Check pin 11. Should be 13.7v. if not check for dirty contacts on wafer or burnt/lifted contact arm. Lift one side of L102 (or remove from circuit) and check voltage at pin 11 again. If 13.7 now,problem lies in area downwind of L102. If still low, follow schematic to Pin 14 on HA1156W. Check pin 14 voltage.
d.) Pin11 on HA1137. Should be 12v.
Click to expand...
Pin 20 - 13.89 vdc
a. H1156 - Pin 4 -12.16 vdc; Pin 5 - 12.17 vdc; Pin 1 - 13.66 vdc
b. Q105-106 were replaced with new KSA992FBU's. ECB were different on KSA992 and properly fitted.
c. S1-2/2 Pin 2 - 13.73 vdc; Pin 3 - 1.86 vdc not 13.7 :(
HA1137 - Pin 2 - 1.922 vdc; Pin 11 - 11.76 vdc; Removed one leg of L102 - Pin 11 - 11.87 vdc
HA1156 - Pin 14 - 3.87 vdc
d. HA1137 - Pin 11 - 11.89 vdc
 
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If we ARE looking at S3, in FM mode Pin 3 should have no voltage other than the 1.9V which might float up from the internal bias of the input comparator. In AM mode, the 13.7V should be switched on to null the FM IF function.
 
I don't know where you got that schematic fragment, both sx-450 manuals I have call your S1 "s3". we're talking about Sx 2/2 F.

Pio1980 tab 2 goes to constant 13.7v from the regulator. tab 3 goes to pin 2 of the ha1137, it specifically is a shut down for the chip input.
 
markthefixer said:
I don't know where you got that schematic fragment, both sx-450 manuals I have call your S1 "s3". we're talking about Sx 2/2 F.

Pio1980 tab 2 goes to constant 13.7v from the regulator. tab 3 goes to pin 2 of the ha1137, it specifically is a shut down for the chip input.
Click to expand...
Clipped from previously posted SX-450 skiz.
https://audiokarma.org/forums/index.php?threads/sx-450-no-am-fm.980616/page-2#post-15285802
Sorry if incorrect, but a faulty switch contact would establish a common mode FM/AM common mode failure as you indicate.
I'll bow out if I'm confusing the OP.
 
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micrometer said:
Ok, The service manual on Hi-Fi engine shows S1 as S3 on the updated schematic I got from Watthour. Confusion solved.

I took a reading at R115 - 1.852 vdc and also at S3 2/2 F at tab 3 - 1.866 vdc

View attachment 2690588

Pio1980 please don't bow out, I need all the help I can get.

Thanks all,
Mike
Click to expand...
If S3F switch contacts check out, then we go to the area around Q302.
Check fuse FU 2 first with a volt meter.
Screenshot_20221017-192900.png
 
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What's the voltage on Pin 2, S3 2/2F? Should be 13.7vdc If you can contact the ROTARY piece that Pin 2 is supposed to contact, meter voltage on that in a free area. Should be same as pin 2. If not, Take a wooden splint (BBQ Match works) and press ever so slightly on Pin2 tab while metering the Rotary piece on the wafer. Somethings either DIRTY as hell or not making contact at the switch.

When you have voltage on the rotary wafer, check PIN3 IN AM, Pin 11 in FM.
 
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micrometer said:
Ok, The service manual on Hi-Fi engine shows S1 as S3 on the updated schematic I got from Watthour. Confusion solved.

I took a reading at R115 - 1.852 vdc and also at S3 2/2 F at tab 3 - 1.866 vdc

View attachment 2690588

Pio1980 please don't bow out, I need all the help I can get.

Thanks all,
Mike
Click to expand...

That voltage at R115 is within reason. The schematic shows S3-2/2 Pin 3 connected to the 13V supply when in AM mode, and not connected in FM mode. The underline in the switch legend (lower left quadrant of the sheet) shows the position of the switch as drawn on the diagram.

Post #46 explains that, as does post #43.
 
larryderouin said:
What's the voltage on Pin 2 ???? S3 2/2F? Should be 13.7vdc If you can contact the ROTARY piece that Pin 2 is supposed to contact, meter voltage on that in a free area. Should be same as pin 2. If not, Take a wooden splint (BBQ Match works) and press ever so slightly on Pin2 tab while metering the Rotary piece on the wafer. Somethings either DIRTY as hell or not making contact at the switch.
Click to expand...
Seconded, do this next.
 
I was NOT criticizing anyone. I should have explicitly directed the first line of my post at the O.P.
in the other line I was answering:

What is voltage @ tab # 2 SW 2/2F?
Click to expand...

Pio1980 tab 2 goes to constant 13.7v from the regulator. tab 3 goes to pin 2 of the ha1137, it specifically is a shut down for the chip input.
Click to expand...

figuring your usage of "tab" to mean switch contact.

Sorry.... no hijack intended.
 
markthefixer said:
I was NOT criticizing anyone. I should have explicitly directed the first line of my post at the O.P.
in the other line I was answering:





figuring your usage of "tab" to mean switch contact.

Sorry.... no hijack intended.
Click to expand...
No umbrage taken, please continue to aid the OP with your expertise. It's a learning experience for us all with many hands on board.
 
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