Troubleshooting Fostex E-16 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

lovebuzz · 17th Sep 2014, 7:57 pm

Quote:

Originally Posted by Dr Wobble

As for using your scope, check your scope ground lead is connected to the ground point that is common to pin 6. If it isnt this may account for your odd reading. Use your DMM on the ohms range to check this is the case.

Yes, I as confused about that ground connector... and I still don't understand which one is the one... Sorry for these newbie's questions, but maybe you could tell me which one I should connect to by looking at the scheme?

lovebuzz · 18th Sep 2014, 9:31 pm

Looking at that scheme I am getting more and more puzzled.. Could it be possible that 6th connector actually IS ground? And erase/bias master oscillator could be 2nd (M.Osc.Con.), 4th (Osc.) or fifth (bias) connector....

Then what they say in manual is such a mess.... :

Quote:

To check the oscillator frequency, the record/reproduce amplifier PCB is pulled out from the E-8 or E-I6, and the frequency checked at connector pin No. 6.

If the oscillator frequency is off spec, adjust the core of T-1 OSC transformer on the system control PCB, to 100KHz, ±0.5KHz.

Has anyone of you guys checked that before?..

jamesperrett · 19th Sep 2014, 1:24 pm

I thought you said that the bias/erase was OK on tracks 1-8? If so, it won't be the master oscillator causing the problem but check continuity between the master oscillator pin on the edge connectors for track 8 and track 9.

According to the channel circuit diagram, pin 6 is the erase head output from the channel card. The oscillator input is pin 4.

Diabolical Artificer · 19th Sep 2014, 2:17 pm

According to diagram Master oscillator is pin 2 with pin 4 also marked an oscillator too.

With the machine turned off, DMM on diode/continuity test and one probe of your DMM clipped to the chassis, go through all the pins untill you get a bleep. Thats a ground. The pin marked mute may be a ground or could it be that pin 2 is the + of your oscillator with pin 4 the GND ?

With your scope have a poke about until you get a good sinewave on the screen. There may be test pads on the PCB - small round gold coloured - which are a good place to look for signals. With the voltages not being that high inside your Fostex, your unlikely to damage your scope.

Andy.

lovebuzz · 23rd Sep 2014, 8:26 pm

Thank you guys for your help! You are giving great tips and directions where I can dig further! Well, I this I've found "the ground" in a bit different way - took out one of the repro/record amplifier PCBs and connected it's ground to one probe of my DMM while checking all pins with the other on continuity check - and 6th pin is indeed the ground. Do you think it's a "legal" way to do it?

But, while I was trying to rise my second Fostex from dead, my first one (a working horse) started to behave in a strange way

Well, the problem is - the input levels bar-graphs are 4 db lower than real signal is... I mean i am feeding my Fostex with 1kHz -10dbv and it was showing 0 on bar-graph before (just as it should), but now it shows -4 db, even though measuring output by AC voltmeter indicates correct figure (-10dbv, the same as what I feed it with).

Now, if I record this signal and play it back, then bar-graph shows correct value of zero (-10dbv), so it's not a problem of meter calibration.. but what it is then?? Maybe you have some ideas?

19th Sep 2014, 1:24 pm	#23
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,875	Re: Troubleshooting Fostex E-16 I thought you said that the bias/erase was OK on tracks 1-8? If so, it won't be the master oscillator causing the problem but check continuity between the master oscillator pin on the edge connectors for track 8 and track 9. According to the channel circuit diagram, pin 6 is the erase head output from the channel card. The oscillator input is pin 4.

19th Sep 2014, 2:17 pm	#24
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,669	Re: Troubleshooting Fostex E-16 According to diagram Master oscillator is pin 2 with pin 4 also marked an oscillator too. With the machine turned off, DMM on diode/continuity test and one probe of your DMM clipped to the chassis, go through all the pins untill you get a bleep. Thats a ground. The pin marked mute may be a ground or could it be that pin 2 is the + of your oscillator with pin 4 the GND ? With your scope have a poke about until you get a good sinewave on the screen. There may be test pads on the PCB - small round gold coloured - which are a good place to look for signals. With the voltages not being that high inside your Fostex, your unlikely to damage your scope. Andy. __________________ Curiosity hasn't killed this cat...so far.

23rd Sep 2014, 8:26 pm	#25
lovebuzz Retired Dormant Member Join Date: Sep 2014 Location: Riga, Latvia. Posts: 15	Re: Troubleshooting Fostex E-16 Thank you guys for your help! You are giving great tips and directions where I can dig further! Well, I this I've found "the ground" in a bit different way - took out one of the repro/record amplifier PCBs and connected it's ground to one probe of my DMM while checking all pins with the other on continuity check - and 6th pin is indeed the ground. Do you think it's a "legal" way to do it? But, while I was trying to rise my second Fostex from dead, my first one (a working horse) started to behave in a strange way Well, the problem is - the input levels bar-graphs are 4 db lower than real signal is... I mean i am feeding my Fostex with 1kHz -10dbv and it was showing 0 on bar-graph before (just as it should), but now it shows -4 db, even though measuring output by AC voltmeter indicates correct figure (-10dbv, the same as what I feed it with). Now, if I record this signal and play it back, then bar-graph shows correct value of zero (-10dbv), so it's not a problem of meter calibration.. but what it is then?? Maybe you have some ideas?