OK folks, I know this is "new" technology.. Well, about 25 years new anyway... I had my trusty Technics Hi-Fi stack powered up for probably the last 15 years without a break, until last weekend, when I pulled the plug for the first time, in all that time. Aside from short duration power failures, it hasn't been without power in all those years. I had to pull the plug to facilitate its relocation, and it was without power for for about a week.. Since then, I've powered it up again and everything works except the tuner.. Now the tuner appears to power on OK, and in fact it is in effect the "master switch" for the entire stack.. The clock works fine, all the control buttons appear to do everything they should, but the tuner is deaf. If I turn up the volume on the amp, I can hear various hums, buzzes, and rasping sounds in conjunction with button presses on the tuner which suggest to me that I'm just hearing the control system commands, and that under normal circumstances these would still be present but not audibly perceptible? If I attempt to scan, on any waveband, the tuner evidently, and visibly, scans the particular band but finds nothing, just as if the tuner itself is dead, but leaving all the power and the control system in working order. I've opened it up, and there is no visibly obvious damage or faults, and I'm at a loss to explain why it was working OK only minutes before the move, and then not working when powered up again, a few days later. There are a tidy few electrolyitcs in this tuner and I'm wondering if one of these has mysteriously died after being left without power? Or is that just my lack of knowledge and understanding of these things? If it had had valves in it, I'm sure I could have sorted it, but transistors and ICs, I'm stuffed I have no service data, and worst of all, no idea.. Does anyone else have a clue? For what it's worth, I can pick up another tuner for around £20.00, but where's the fun in that? Marion
Hi Marion, I had a look on the Panasonic technical site, and they do not have any service info. listed for this model, only the user manual. (which I can e-mail or upload via Chris). This fault report taken from the TV mag.
#3 Technics STX990L tuner The reported fault with this standalone tuner, part of a complete hi-fi system, was no stations being received. Once it was on the bench it was clear that there was no AM or FM reception. Some quick checks proved that the relevant oscillator and audio preamplifier circuits were working, but when I checked around IC201 no IF signal could be detected and most of the voltages appeared to be incorrect. The cause of the trouble was eventually traced to the IF transformer Z202. There was normal reception once a replacement had been fitted
Hi,
That would appear to sum up the symtoms exactly.. Trouble is, if it's an IF transformer, where on Earth will I find such an antique?
To be honest, I probed around the IF section with my Fluke 117, and couldn't find any meaningful voltages.. There were a lot 0.000v readings, or the odd 0.145v.. So I'm guessing it'll be that transformer.. I'll have a closer look tomorrow.
I would surmise a replacement tuner may be the only practical answer after all.. weird how it failed that way though.
Marion
I would not take that particular fault report as gospel, as that fault was listed in 2003, it is the only fault listed in the mag, but there could be many other causes, like you say a missing supply is but one other alternative.
Unless there is corrosion I'd not suspect the/an IFT (which likely can be replaced). Isn't there more than one and separate 455 and 10700 KHz types, or has the tuner got ceramic filters and then there are only a couple of matching IFTs, one for 10.7 and one for 455?
Check to see if LO is running.
Have you a scope? An analogue one even rated at 20MHz can "see" VHF up to 150MHz with a good probe, but a 20MHz sampling Digital one can only be used up to about 1MHz (or 2MHz if switchable to single channel sampling)!
Marion, if you've got an IC with no supply voltage, that is pointing you in the right direction!
You should be able to find data for the chip online - that will tell you which is the supply pin. Then trace it back to the PSU until you find out where it's getting lost.
No different to valves, really - as far as supply faults are concerned - except the voltages are lower!
When all else fails, read the instructions
An interesting development tonight..
Lastnight, I left the stack powered into standby mode, which just barely raises the temperature in the casing, but.... When I turned the Hi-fi on, in radio mode, I got the same symptoms as lastnight, along with momentary 'spits and spots' of sound coming through.. Left on for a few minutes, the tuner would burst into life for a second or two before going silent again.
It will now give the same spits and spots and momentary burst for as long as I leave it turned on..
Should I be looking at dry joints perhaps? or maybe some intermittent fault of a thermal nature?
Michael..
Yes, I have a scope, but not the expertise to use it.. At least not to use it properly.. I've been trying to find a local college with a friendly physics tutor, who might teach me the essentials.. The scope has been locked away for a couple of years, but I believe it is 40MHz.. It's an Isotech (RS Components) definitley analogue, and dual trace.
I also have a Fluke 117 multimeter, which has a Hz feature, but without an instruction manual, I don't know what it's frequency range covers, though I assume it will be pretty low?
My next plan of action was to have a general close inspection and solder-up.. A sort of 'blitz' on dry joints?
Marion
The frequency meter on DMM is only of use to look at output of a generator at quite high level.
Hi Marion, You can get the instruction manual and specs for your Fluke direct from Fluke here: http://www.fluke.com/fluke/usen/Digital ... ?PID=55996 You are correct, it does not go high enough in frequency for this application. may be worth running a hairdrier in the back for a couple of minutes to see if you have a thermal fault, capacitors that only work when warm and the like. I had a look about the usual free sites, but none seem to have a circuit for this, a couple of pay for ones though.
The frequency meter on DMM is only of use to look at output of a generator at quite high level.
Hi Michael, Not very high at all really.. Two ranges; 5Hz to 50Hz, and 45Hz to 5KHz. I'll need to seek out the scope.. I know where to find it, it's just locked away and buried amongst a lot of other stuff Marion
Hi Marion, You can get the instruction manual and specs for your Fluke direct from Fluke here: http://www.fluke.com/fluke/usen/Digital ... ?PID=55996 You are correct, it does not go high enough in frequency for this application. It may be worth running a hairdrier in the back for a couple of minutes to see if you have a thermal fault, capacitors that only work when warm and the like. I had a look about the usual free sites, but none seem to have a circuit for this, a couple of pay for ones though.
Hi, I have the manual now Thanks.
It may be worth running a hairdrier in the back for a couple of minutes to see if you have a thermal fault, capacitors that only work when warm and the like.
Hmm, a hairdrier.... If only I had one! That does go back somewhat to my feeling about faulty caps, especially with all those little electrolytics that are lurking in there. Marion
Hi Marion.
R to B's idea of a hairdryer is good.....part of the standard kit when trying to find duff electrolytics. Don't get it too hot but aim it at electrolytics for a few seconds to raise the temperature to around 40 - 50 degrees.
The spits and spots of noise you are getting suggest a muting problem (it will have interstation muting). However it depends on how the muting is acheived. A noisy supply rail could trigger the muting which again points to an electrolytic problem.
Leaving it powered and then getting intermittent sound like you are is a classic symptom of tired caps and the hairdryer should help to locate it (them).
Rich.
Edit: If a hairdryer is not available, maybe you can think of some idea to direct some heat into a small area....
If a hairdryer is not available, maybe you can think of some idea to direct some heat into a small area....
Would it work if I touched the tops of the electrolytics with a hot soldering iron? or would that risk doing damage? By which I mean, most of these caps are tiny, around 5 or 6 mm diameter.
Marion
I managed to find a diagram for the ST-X99L on the block diagram, this model uses mainly ceramic filters, but a combined AM/FM IF detector IC. If this manual is anywhere near the same model as yours you are welcome to it, it is a Pdf just under 4meg.
Would it work if I touched the tops of the electrolytics with a hot soldering iron? or would that risk doing damage? By which I mean, most of these caps are tiny, around 5 or 6 mm diameter.
Marion
You can do it that way but it can be messy in as much as it can melt the plastic sleeve if you touch it with the iron and then things look untidy. In my previous life as a service engineer, I had been known to use my gas hot-air pencil that I used for desoldering Philips 'painter' chips* in the field. With this device aimed at an electrolytic from about an inch away for a few seconds, I could locate duff ones fairly quickly.
Rich
*surface mounted control IC.
I have uploaded a copy of the ST-X999 manual to my mediafire account, I will leave it there for a couple of days, if anybody wants a copy they can download it from here: http://www.mediafire.com/view/?d7do6926ew82sjz This then may help Marion, and/or other posters can help too. This manual may be very similar to the model required, apologies if it is nowhere near
OK... I'm back.. I just had to pop out for minute there to get the 'scope, and some audio leads so that I can connect up the tuner to an amp. I'll need to "reconfigure" the Hi-Fi stack, to take the tuner back out the stack for working on. Cuppa tea, anyone? Mine's just brewing in the pot I'll be back again, in a minute or two.... Marion >>EDIT<< Red to Black.. I've tried to download the PDF, but it doesn't seem to want to come down.. I had this problem a week or two ago, and had to leave it 24 Hrs or so before I could get the download I was after. For the record, the 999 looks physically identical to the 990.. I have no idea what the difference is, but I assume there must be a difference Marion
The 999 is possibily a Pan European model ?, I don't know for sure.
I have sent you a PM to try and e-mail it, maybe Chris or one of the Mods can download it and put it in the library ?
Mediafire is ghastly...
Yes Michael mediafire can be a bit hit and miss Can I take mine down now then ?, I don't like leaving manuals and the like on for long
