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Old 27th Jul 2020, 4:19 pm   #1
Michael Maurice
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Default Fidelity AVS2000

i have been asked to repair this, God knows why! The fault was that the channel indicator was stuck on 8 and there was no sound.

What had happened was that heatsinks are attached to the sound o/p chip by plastic screws and they had failed. The 15R resistor in the supply had also failed.

These were replaced but upon switching on, although the channel indicator was showing 1, the resistor was getting very hot.

Does anyone have a circuit for this set?
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Old 27th Jul 2020, 4:43 pm   #2
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Default Re: Fidelity AVS2000

Whilst I no longer have the manuals here is two fault reports C/O the TV mag, one is for the AVS1600 but they are similar in that part of the chassis.


Quote:
#3 Fidelity AVS2000

The fault report read "stuck on channel 8". This was true,
hut there was no audio either. The middle fuse (1A) of the
three attached to the side of the record deck had blown.
This fuses the bridge rectifier on the audio panel. Lifting
R379, the feed to the 12V regulator, proved that the fault
was due to the bridge or the audio output chips. The bridge
was innocent, but both IC4 and IC5 were short-circuit.
Two new TDA1908As and a new fuse restored normal
operation. Stuck on ch.8 was of course due to there being
no 12V supply to the M104B1 chip. A.S.
Quote:
#4 Fidelity AVS1600

There was no sound and the set was
stuck on ch. 8. Sound was restored
by replacing a faulty TDA1908A
chip and fuse. But the set was still
stuck on ch. 8 with the balance
control and remote control unit
having no effect. Checks around the
M104B1 chip IC1 showed that its
5V supply at pin 14 was missing.
The cause was the 5.1V zener diode
5D1 which was short-circuit. Then
we just had to reassemble it all! G.R.
The AVS1600 fault sounds plausible for your fault, which I think I have had before too.
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Old 27th Jul 2020, 4:46 pm   #3
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Default Re: Fidelity AVS2000

Thanks but I cant find 5D1 for love nor money, and both TDA1908A's were replaced.
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Old 27th Jul 2020, 4:52 pm   #4
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Default Re: Fidelity AVS2000

We used to throw these off the 23rd floor of run down tower blocks. Good luck with it Maurice. You will need it. Regards, John.
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Old 27th Jul 2020, 5:11 pm   #5
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Default Re: Fidelity AVS2000

Check out this website's post on 21 September 2011 by gezza123 on Fidelity avs2000

He is still posting and so with any luck a PM to him will provide all the circuits you need.

Chris
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Old 27th Jul 2020, 7:10 pm   #6
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Default Re: Fidelity AVS2000

You're a brave man, Mr Maurice!
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Old 27th Jul 2020, 8:47 pm   #7
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Default Re: Fidelity AVS2000

Good luck Michael,these were designed by the Devil.
Johns remedy looks best.

Dave
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Old 27th Jul 2020, 9:26 pm   #8
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Default Re: Fidelity AVS2000

Michael, the AVS2000 uses the Fidelity ZX3000 chassis and is listed in the Radio and Television Servicing book 1985/6. I have a copy of this so could scan it if required.
The audio chip, IC3, TDA8190G has a 25V supply fed to pin 18 via R26 (10 Ohm) I can't see a 15 Ohm resistor that you mentioned in post #1.

It's a fair bet the IC is faulty drawing excess current causing R26 to overheat. It's also worth checking C21, 1000uF 25V which smooths the 25V supply to the audio chip.

Regards,
Symon

Last edited by Philips210; 27th Jul 2020 at 9:44 pm.
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Old 27th Jul 2020, 9:40 pm   #9
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Default Re: Fidelity AVS2000

Hi

I just noticed there's an earlier version of the ZX3000 chassis shown in the R and TV servicing book 1984/5. In that chassis a different audio chip is used - a TDA3190 but I don't think this version applies to the AVS2000.

Regards,
Symon.
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Old 27th Jul 2020, 10:01 pm   #10
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Default Re: Fidelity AVS2000

Hi Symon,
The AVS XXXX sets were quite a bit different to the usual more common garden ZX3000 sets, the different chipsets used in the small signal and remote sections were the main differences, most of the PSU and Lopt stages were very similar though
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Old 27th Jul 2020, 10:12 pm   #11
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Default Re: Fidelity AVS2000

Hi Red to Black.

Thanks for pointing that out. I've often found the Radio and Television Servicing books don't always get the information presented accurately. I had a suspicion the circuit I was looking at may have been different to Michael's due to his mention of a 15 Ohm feed resistor.

Regards,
Symon
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Old 27th Jul 2020, 10:16 pm   #12
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Default Re: Fidelity AVS2000

The scart and internal/external AV switching was a lot more complicated/elaborate on these versions of the ZX3000 chassis too.
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Old 27th Jul 2020, 11:21 pm   #13
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Default Re: Fidelity AVS2000

Both TDA8109A’s were replaced, but the resistor still smoked. I will try to order a service manual.

I agree it is a horrible set but the owner wants it repaired and as they say the customer is always right.
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Old 27th Jul 2020, 11:41 pm   #14
Philips210
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Default Re: Fidelity AVS2000

Hi.

I don't know if it's worth doing a resistance check on the supply pin of the audio ICs to chassis. The supply smoothing capacitor(s) may be worth checking for being s/c or leakage.

Regards,
Symon.
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Old 28th Jul 2020, 7:02 am   #15
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Default Re: Fidelity AVS2000

I would remove both TDA8109A’s again and run the set without them. You could have a faulty IC!

We’ve all fallen for the, ‘it’s a new part so it’s ok’, scenario before!

Best of luck, it’s been a good few years since I’ve had to repair one of these.


SimonT.
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Old 28th Jul 2020, 8:11 am   #16
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Default Re: Fidelity AVS2000

According to the circuit diagram the two TDA1908A chips are supplied directly from D308, D309, D310 and D311 in bridge format. IC7, L7812 a 12v regulator is fed by R379, which is a 15 ohm 1.6w resistor. C354 (3300uf) is across the bridge side of R379 and C352 (47uf) reg input end of R379. C351 (1000uf) is across the output of the reg. If R379 is overheating then the reg could be faulty, as well as C352 / C351, also check that the bridge diodes have not suffered and are letting excessive ac through to C354. After that see if there are any shorts to ground on the output of the reg.
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Old 5th Aug 2020, 10:09 pm   #17
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Default Re: Fidelity AVS2000

All done and working.

The 12V line goes to a number of chips including IC3 TDA3810, however this chip is supplied by a diode D307. The chip had gone nearly short circuit, but you couldn't tell by measuring the 12V line and resistance checks proved futile. Replacing the IC cured the fault.
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Old 5th Aug 2020, 10:37 pm   #18
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Default Re: Fidelity AVS2000

Excellent!

I've got one of these sets and its never gone wrong (other than the belt that drives the record player in and out) in 25 years or so, but I suspect the previously mentioned C21 probably needs investigating sometime, as it's developing a bit of mains hum on the audio. I'm actually a bit cross that there's another working example out there now - I thought mine was the only one left in the UK!
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Old 6th Aug 2020, 3:57 pm   #19
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Default Re: Fidelity AVS2000

Quote:
Originally Posted by Techman View Post
I thought mine was the only one left in the UK!
Unfortunately not! John.
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Old 6th Aug 2020, 5:51 pm   #20
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Default Re: Fidelity AVS2000

Just after these sets came out, our SEME rep appeared one day with re-chargeable screwdrivers. Just the job for removing the 20 odd screws that held the back cover.

Alan.
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