| Contents
1. Why did my power supply fail?
2. Why is the audio distorted?
3. Why are the pictures "sparkly" on strong stations?
4. Symptom: all display segments are lit and nothing else happening
5. Martin Johnson's recommended LT8700 web sites |
1. Why did my power supply fail?
This is quite often caused by the failure of R16 or R17 which are 100k resistors near the centre line of the Power Supply Board. SatCure supplies a replacement type rated at 350 volts which should *never* fail again. For safety and reliability please order 2 x 100k/350v resistors.
2. Why is the audio distorted?
I'll let Kevin Lamb answer this. He came up with the question then found the solution by himself!
> I have a 3year old Echostar LT-8700 rcvr. It is connected to a 90CM
> dish with a Cambridge Gold Universal LNB.
>
> When tuned in to strong satellite channels (e.g. UK Gold and
> Discovery on Astra) then the audio is distorted on loud parts (e.g
> during adverts or close miked female vocals, narration etc.). It
> manifests itself as sibilance. The receiver has always done it but
> it has now started to annoy me. It sounds like the the audio is
> being clipped or otherwise distorted on signal peaks. The sound is
> fine (i.e not distorted) when tuned into D2MAC channels and many
> (presumably lower recording level) VC channels.
>
> It is as if a audio signal level is too high somewhere (presumably
> pre STV0030) maybe bottom end of a potential divider fallen off etc.
I have alleviated the problem by changing the crystal on the TUNER PLL
which feeds the HITS circuit (Y1). The service manual specifies a
24MHz Crystal but the circuit diagram shows 8MHz and the fitted part had
8.000MHz printed on the can (It was a RADIOTRON part) so I replaced it with
an IQD 8.000MHz crystal (Marked 8.000MHz UA). This has improved the sound
and almost completely eliminated the problem. The sound is much better. Some
channels are still slightly sibilant but the sibilance is much reduced and
does not turn in to gross distortion and give the overloaded (spitty) sound.
The audio is now optimal when the bandwidth of the audio is set to the
published standards (rather than set high as it was before).
Note: SatCure stocks 8.000MHz crystals.
3. Why are the pictures "sparkly" on strong stations?
The LT8700 has a "Low Threshold" tuner which is designed to receive weak signals. If you have a large dish, a high gain, low noise LNB and low-loss cable - well, you are pretty stupid to point it at a strong transmission!
4. Symptom: all display segments are lit and nothing else happening.
Replace R223 & R224 10ohm 1/10W (SMD) on the underside of the board.
They power the STV0030 chip.
Note that on older boards these are labeled R213, R214
> Just a few lines to say many thanks for your advice on
> troubleshooting and repairing my satellite setup. In my previous
> messages I described how my Echostar LT8700 was displaying a "motor
> error" message on screen whenever any dish movements were attempted.
> Your original diagnosis suggested that the reed switch in the motor
> had failed and was not sending motor pulses back to the receiver. I
> decided to completely strip down the motor and discovered that it
> used a system of opto - electronics to send pulses to the receiver.
> A beam of light passing through a slot in one of the gear wheels in
> the motor was broken at regulat intervals as the gear rotates thus
> triggering the pulses. The problem was that although a beam was
> being produced it was not being detected due to the failure of this
> component. I am relieved the motor is again fully functional as it
> now seems impossible to obtain spares for Fibo gregorian dishes in
> this country. I must say I was suprised to see this method of
> pulsing employed in the motor as it was not what I expected to find.
> Anyway, I thought you might like to know how I got on and also take
> the opportunity to share my experiences repairing this fault. Thanks
> again for your help and the excellent information contained in your
> site which I have shared with my fellow enthusiasts. Best regards,
> Paul Austin... A complete fault-finding guide called "The Satellite Repair Manual V" is available.
+echostar +lt +8700 LT-8700, SR-8700