Onkyo TX-4500 Receiver signal reception fix

Hi all, This relates to part of a thread I started in the Vintage Solid State forum. I think this would be the best place for the part related to the tuner problems. I didn't see any info on what I discovered but probably many already are familiar with my new-to-me discovery. I have no idea if this would be applicable for other tuners. I hope it will be useful to someone.
I accidentally discovered why my receiver was not pulling in many stations and the signal meter appeared to be not working. I don't necessarily know the right terminology as I am new to this so please bear with me.
ok so a little background; the signal meter hardly responded- you could just barely notice a little twitch on strong close-by stations and most stations had tons of noise or were no longer found (certainly none would 'lock'). I hadn't used this receiver in many years as it had a blown fuse (that I found through some help on this site with getting the service manual). I was assuming the meter was dead but also wondered if something else had been damaged when the fuse blew. So I searched though this Tuner forum and found the great sticky about cleaning a tuner. Well I don't have the correct cleaners so I thought to check if everything was tight as someone mentioned finding loose screws that might cause problems. So i find these 6 screws on top on the 'fin box'. 5 look the same and the one furthest to the left is smaller and colored orange. I find some of the 5 are loose so I tighten them all down and turn on the radio and notice now I am getting strong AM and the meter is moving much more. I switch to FM and absolutely nothing no stations at all!! So I go back and loosen some of the screws and the FM comes on strong with perfect meter action. Well I play with this a bunch and get the best position for each screw for AM and FM (2 of the screws seemed to influence AM and 3 FM). I also had messed with the little orange color screw and noticed that it moved the position of the stations on the dial! This was a great discovery as the stations were not on the right numbers. So i adjusted this and now all the station #'s are correct. It seems that this function was intended but I wonder if the other 5 screws are supposed to do what they did or if it is a sign of some other problem. I am just happy i got it receiving better than it has in the last 25 years!! I bought this new in 78.
Now I need to decide if I am going to be brave enough to try to replace the tuner indicator needle light and some other lamps that need to be soldered in. I hope my stumbling on to this will be helpful to someone. peace, Mbira

I think you are talking about the air cap tuning screws.

Either I don't understand enough about RF or you are the luckiest person here.


My understanding ells me to never, never, never muck with the screws on the air cap.

Those "screws" are the trimmer capacitors for the tuning section. The one that changed the frequency is for the local oscillator. The others are tuned to max reception. The two big sections of the "finned thing" are for tuning the AM. The smaller (usually 2-4 vanes) sections are for the FM. The procedure is in the manual - normal is to adjust the inductor associated with that section of the tuning cap at a station at the low end of the dial ( 90 mHZ or so) then adjust the trim cap at the high end of the dial (106 mHZ or so.) You have to do the tuning frequency (local oscillator) first, for the other adjustments to be optimal. Cleaning the tuning capacitors is important because dirt and dust can cause the tuning to change, which means you would have to retune it after cleaning. Hopefully the inductors are close enough - Given what you've already done, I would max the signal at the upper end of the band for the other tuned circuits, and see how it works. Good luck.

thanks for the replies. Here are a couple photos of the screws I am talking about so that is clear. Let me know if you were both talking about these same screws. I don't know the names of these things and I have a hard time reading schematics. But I would like to learn as much as I can because I love vintage stereos.

sregor said:

Those "screws" are the trimmer capacitors for the tuning section. The one that changed the frequency is for the local oscillator. The others are tuned to max reception. The two big sections of the "finned thing" are for tuning the AM. The smaller (usually 2-4 vanes) sections are for the FM. The procedure is in the manual - normal is to adjust the inductor associated with that section of the tuning cap at a station at the low end of the dial ( 90 mHZ or so) then adjust the trim cap at the high end of the dial (106 mHZ or so.) You have to do the tuning frequency (local oscillator) first, for the other adjustments to be optimal. Cleaning the tuning capacitors is important because dirt and dust can cause the tuning to change, which means you would have to retune it after cleaning. Hopefully the inductors are close enough - Given what you've already done, I would max the signal at the upper end of the band for the other tuned circuits, and see how it works. Good luck.

Click to expand...

Thanks Steve! Can you tell me where the inductors are? Are they in the photos I uploaded? I have noticed that there is no reception at the bottom 1 1/2" of AM dial. How do I know which inductor is associated with which screw (trimmer capacitor)? I picked some FM stations I like and tuned the screw(s) to get those in the best. Can setting this up wrong do any damage to it? Do they go into how to do this in the manual you have? I can't find much to help me (at my beginner level) about this procedure in the service manual I downloaded. thanks again, Mbira

blhagstrom said:

I think you are talking about the air cap tuning screws.

Either I don't understand enough about RF or you are the luckiest person here.


My understanding ells me to never, never, never muck with the screws on the air cap.

Click to expand...

is the air cap the thing with the tuning fins that rotate when you turn the tuning knob? see the photos I uploaded because I don't know the proper name.

Mr Mbira said:

is the air cap the thing with the tuning fins that rotate when you turn the tuning knob? see the photos I uploaded because I don't know the proper name.

Click to expand...

Yes, the air cap is the thing with fins.

Tuners are pretty complicated things to be mucking with if you do not know how they work and if you don't have the proper test equipment and knowledge to be messing with them. Although how they work and what the parts do is not magic, it is a bit involved.

I am surprised you haven't completely messed yours up.
If its working now, I recommend you leave it alone.

Front end alignment basics - I'm not responsible use at your own risk

Tools: Plastic alignment tools are a must. Metal allen wrenches change the tuning, and can break ferrite cores if not careful.

First - basic mechanical alignment - make sure the pointer goes from one end to the other as you turn the tuner from one end to the other.

Second - local oscillator adjustment. Find a know station on the low end of the dial (around 90mHZ and set tuning indicator on that station. Adjust inductor (L6 - even though manual says L0) and turn off quartz lock (Touching the knob should turn it off - I don't know of the top of my head if there is a switch for this.) Reminder - US FM stations are at odd tenths - there is no 90.0, but 89.9 or 90.1 (or .3 or .5 or .7 and so on.) Once it is tuned, set the pointer to a station at the upper end of the dial, and adjust TC-6 until the station is tuned in. Repeat these 2 steps until you are satisfied with the tuning point. The general theory is the inductor affects both ends of the dial equally, and the trimmer caps (those screws you originally adjusted) affect the higher frequency tuning more, but both interact. Usually back and forth 2 times is enough, unless really bad. As mentioned previously, it is better to clean the tuning condensers(the fins) and a drop of deoxit where they rotate before doing adjustments.

After doing the tuning adjustments, the tuned circuits in the front end are tweaked. Same basic process except works best with weaker stations. Find a weak station at the low end, adjust inductos L1, L2 and L3 for maximum signal strength, the tune to a weak station at the top end, and adjust trimcaps TC-1, TC-3 and TC-4 for maximum signal strength. Back and forth a couple of times should do it. Same basic concept - the inductors affect both low and high, the trimmers affect the higher tuning frequencies more.
L5 is for the IF and requires signal generator and scope for proper alignment, so don't mess.

TC-5 is adjuster for the AM tuning frequency.TC-2 is for AM sensitivity. The inductors are on the main tuner board.

thanks so much Sregor this seems doable. Thanks for all the clear detailed explanations!!! That helps immensely!! It is so great to now see how it all works after just hacking my way through it. The only question I have so far is; Are you saying L-0 is L-6?? My service manual does not include this information and it is a bad copy and some labels are unreadable... is there a way to download the one you have? Also it is difficult to see into the inductors do you know what the drive shape is ie; hex, philips, etc? Would wood be ok or should i only use plastic? thanks again!

I down loaded the manual from http://www.hifi-manuals.com/Onkyo/page-15 which was linked in one of your other threads. It's ok not that great.
The L0 L6 being the same is based on the schematic and my own general knowledge. The manual is confusing.....
Wood would be okay. Plastic ones are available from electronic supply places. Used to be Radio Shack, but not sure where to get them these days The inductor cores are turned with a hex head (allen type). They look like round holes in your pictures, but if you look carefully you'll see the six sided holes. Good luck.

sregor said:

I down loaded the manual from http://www.hifi-manuals.com/Onkyo/page-15 which was linked in one of your other threads. It's ok not that great.
The L0 L6 being the same is based on the schematic and my own general knowledge. The manual is confusing.....
Wood would be okay. Plastic ones are available from electronic supply places. Used to be Radio Shack, but not sure where to get them these days The inductor cores are turned with a hex head (allen type). They look like round holes in your pictures, but if you look carefully you'll see the six sided holes. Good luck.

Click to expand...

OK thanks for the clarification. Now I see where you got the chart from ...I expected the diagram to be right next to it like in your post. I will check radio shack or maybe just make some. thanks for your patience, Mbira

sregor said:

Front end alignment basics - I'm not responsible use at your own risk

Tools: Plastic alignment tools are a must. Metal allen wrenches change the tuning, and can break ferrite cores if not careful.

First - basic mechanical alignment - make sure the pointer goes from one end to the other as you turn the tuner from one end to the other.

Second - local oscillator adjustment. Find a know station on the low end of the dial (around 90mHZ and set tuning indicator on that station. Adjust inductor (L6 - even though manual says L0) and turn off quartz lock (Touching the knob should turn it off - I don't know of the top of my head if there is a switch for this.) Reminder - US FM stations are at odd tenths - there is no 90.0, but 89.9 or 90.1 (or .3 or .5 or .7 and so on.) Once it is tuned, set the pointer to a station at the upper end of the dial, and adjust TC-6 until the station is tuned in. Repeat these 2 steps until you are satisfied with the tuning point. The general theory is the inductor affects both ends of the dial equally, and the trimmer caps (those screws you originally adjusted) affect the higher frequency tuning more, but both interact. Usually back and forth 2 times is enough, unless really bad. As mentioned previously, it is better to clean the tuning condensers(the fins) and a drop of deoxit where they rotate before doing adjustments.

After doing the tuning adjustments, the tuned circuits in the front end are tweaked. Same basic process except works best with weaker stations. Find a weak station at the low end, adjust inductos L1, L2 and L3 for maximum signal strength, the tune to a weak station at the top end, and adjust trimcaps TC-1, TC-3 and TC-4 for maximum signal strength. Back and forth a couple of times should do it. Same basic concept - the inductors affect both low and high, the trimmers affect the higher tuning frequencies more.
L5 is for the IF and requires signal generator and scope for proper alignment, so don't mess.

TC-5 is adjuster for the AM tuning frequency.TC-2 is for AM sensitivity. The inductors are on the main tuner board.

Click to expand...

Thank you very much for your help. I could successfully align FM on my TX-4500.