Hiya.
My tuner has a problem. It powers up fine but it doesn't seem to be receiving any signal at all. The dial mexhNism is still connected and turning normally but none of the ariel inputs seem to work, both am and fm. The fuse seems fine and I can't see any signs of anything that's burnt out.
I love this tuner and would hate to see it go. Any suggestions gratefully received.
My tuner has a problem. It powers up fine but it doesn't seem to be receiving any signal at all. The dial mexhNism is still connected and turning normally but none of the ariel inputs seem to work, both am and fm. The fuse seems fine and I can't see any signs of anything that's burnt out.
I love this tuner and would hate to see it go. Any suggestions gratefully received.
The good news is that it is both AM and FM. Look inside for more fuses and did it used to have a mute relay click after power up?
Check the power supply. There's a single regulated 12.8V supply that powers the whole tuner.
Even if the front panel is lit, it doesn't mean the rest of the tuner is getting power. The front lamps excluding the stereo and lock LEDs are derive their power before the regulator.
Refer to the schematic here -> http://akdatabase.org/AKview/albums/userpics/10004/Pioneer TX7800 Schematic.pdf
Even if the front panel is lit, it doesn't mean the rest of the tuner is getting power. The front lamps excluding the stereo and lock LEDs are derive their power before the regulator.
Refer to the schematic here -> http://akdatabase.org/AKview/albums/userpics/10004/Pioneer TX7800 Schematic.pdf
Join the fmtuners group at yahoo and check out Tuner Information Center at: Tuner Information Center - Vintage Stereo Tuners
It is unlikely that you are going to find something that you can fix yourself, but it is at least possible with the guidance of some of the more experienced members at the above site.
Worst case there are a number of guys over there who service FM tuners and you could send it to one of them.
It is unlikely that you are going to find something that you can fix yourself, but it is at least possible with the guidance of some of the more experienced members at the above site.
Worst case there are a number of guys over there who service FM tuners and you could send it to one of them.
Hi guys,
Thanks for the quick responses. In answer to your questions...Simon I think there is a relay but it was a protection one that came in if you unplugged the ariel, if you turned the unit off and on again it reset it. I'll cheack again for fuses, do you think there is anything to check on the underside of the board itself...I dont really want to do that myself as I'm still a novice.
Hitachi_nut, the PS is encased, would I be able to check it without taking it apart, perhabe at the powerplug input at the back of the machine? I'll have a look at the schematic, my knowledge is quite basic but I think I can give it a go...any areas that you could suggest might be the culprit othet than the psu?
Kevin, I think I'd like to have a go at fixing myself, I'm enjoying tinkering with stuff more as time goes on, I know where to draw the line though, I think! If I'm stumped I'll get a pro to do it.
Does anyone one think it's worth changing the caps or op amps or do you think it would ruin the character of the sound?
Thanks for your help and please excuse my ignorance on certain things, I'm still learning.
Thanks for the quick responses. In answer to your questions...Simon I think there is a relay but it was a protection one that came in if you unplugged the ariel, if you turned the unit off and on again it reset it. I'll cheack again for fuses, do you think there is anything to check on the underside of the board itself...I dont really want to do that myself as I'm still a novice.
Hitachi_nut, the PS is encased, would I be able to check it without taking it apart, perhabe at the powerplug input at the back of the machine? I'll have a look at the schematic, my knowledge is quite basic but I think I can give it a go...any areas that you could suggest might be the culprit othet than the psu?
Kevin, I think I'd like to have a go at fixing myself, I'm enjoying tinkering with stuff more as time goes on, I know where to draw the line though, I think! If I'm stumped I'll get a pro to do it.
Does anyone one think it's worth changing the caps or op amps or do you think it would ruin the character of the sound?
Thanks for your help and please excuse my ignorance on certain things, I'm still learning.
irishiranian,
The power supply/regulator that I'm taking about is the circuit board after the transformer. I don't think it is encased at all judging from the pictures of the TX-7800 on the net. If you can't figure this out by yourself, try locating a knowledgeable tech in your area who can do it.
I think an alignment would produce more benefits than just upgrading the existing caps and op amps. The TX-7800 is over 30 years old and there is a 99.9% chance it needs an alignment if it wasn't done recently already. If the FM discriminator is out of alignment and producing more than 1% THD, not even the most expensive op amp and boutique film capacitor will be able to fix this.
Listen to kevinkr's suggestion and do a lot of reading on the FM tuner site & Yahoo forum.
The power supply/regulator that I'm taking about is the circuit board after the transformer. I don't think it is encased at all judging from the pictures of the TX-7800 on the net. If you can't figure this out by yourself, try locating a knowledgeable tech in your area who can do it.
I think an alignment would produce more benefits than just upgrading the existing caps and op amps. The TX-7800 is over 30 years old and there is a 99.9% chance it needs an alignment if it wasn't done recently already. If the FM discriminator is out of alignment and producing more than 1% THD, not even the most expensive op amp and boutique film capacitor will be able to fix this.
Listen to kevinkr's suggestion and do a lot of reading on the FM tuner site & Yahoo forum.
There's only one opamp, a NJM4558DV, which used for the auto fine tune. When you touch the tuning knob, as in tuning in a station, it disables the AFC (automatic frequency control) and re-enables it when you "let go" of the tuning knob. So changing it would have no bearing on the "character of the sound".
Now the PA1002A is an AF amp/de-emphasis/muting IC. Have you checked to see if there's any output coming from the DET OUT HORZ jack while on the FM band? It will have a very "treblely" sound. Do the tuning meters move as you turn the tuning knob while having an aerial hooked up? Is there any hiss or noise coming from the audio out jacks?
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Hello again,
Hitachi nut, thanks for the tip, will def get it realigned once it's fixed.
Cogsncogs. There is no sound at all coming from the FM or AM on either the fixed or variable. The dials are all dead across the whole spectrum...quite literally the lights come on but there's no one at home. There's no hiss and even if I turn the amp up loud and the output to full you can't hear any sound leaking through at all. I'm afraid I have no idea what a DET OUT HORZjack is and after searching on the web, it seems there area few diff types of Horiz. Any chance you could post a link to help a novice out!
Thanks again guys and sorry if my lack of knowledge is frustrating!
Hitachi nut, thanks for the tip, will def get it realigned once it's fixed.
Cogsncogs. There is no sound at all coming from the FM or AM on either the fixed or variable. The dials are all dead across the whole spectrum...quite literally the lights come on but there's no one at home. There's no hiss and even if I turn the amp up loud and the output to full you can't hear any sound leaking through at all. I'm afraid I have no idea what a DET OUT HORZjack is and after searching on the web, it seems there area few diff types of Horiz. Any chance you could post a link to help a novice out!
Thanks again guys and sorry if my lack of knowledge is frustrating!
Have you checked the basics... that all the supplies are correct at various points in the tuner ?
Refer to the circuit in post #3 locate transistor Q1 in the power supply which may be fitted to or fitted with a small heatsink.
With your meter on DC volts measure the voltage from ground (chassis) to the 3 legs of the transistor in turn. Be extremely careful not to short any leads together.
You should read around 12 to 13 volts on the two outer leads and around 20 volts or just over on the middle lead.
Thats your first step 🙂
With your meter on DC volts measure the voltage from ground (chassis) to the 3 legs of the transistor in turn. Be extremely careful not to short any leads together.
You should read around 12 to 13 volts on the two outer leads and around 20 volts or just over on the middle lead.
Thats your first step 🙂
Given that it is dead on both AM and FM it is likely to be a fault in the PSU or audio end. This is good, because fiddling with the RF/IF end is likely to end in tears unless you really know what you are doing and have the appropriate test equipment.
I understand that in the old days of radio and TV repair shops it was quite common for a customer to come in and say "I have tightened up all the loose screws in this radio, and now it doesn't work!" If you don't understand this joke, then don't touch the RF end!
I understand that in the old days of radio and TV repair shops it was quite common for a customer to come in and say "I have tightened up all the loose screws in this radio, and now it doesn't work!" If you don't understand this joke, then don't touch the RF end!
Thanks for your help, I will have a look at it in the next couple of days. (Just to perfectly demonstrate my ignorance, I need to check with you all that the unit shoutldn't be plugged in when I am testing the values you mention above.)
It has to be plugged in and switched on to measure voltages 🙂
Its all low voltage but just be careful you don't short anything out... steady hands 😉
Edit,
Not sure if you saw this regarding your Micromega,
http://www.diyaudio.com/forums/digi...odification-incorrect-info-3.html#post2592594
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