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Old 23rd August 2010, 02:27 PM   #1
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Default fault diagnosis on 2 Heybrook amps

Hi guys, I'm trying to diagnose & repair two related Heybrook amps. One is the Integra which is a competent integrated amp. The other is the Teg70 which is designed to work in conjunction with the Integra to enable bi-amping.
Both amps are around 10-12 years old and have simply laid out channel symmetrical pcbs.

The Integra hisses badly on one channel on power-on with the hiss dwindling to nothing after 45 seconds or so. The sound from it is nothing like as clean as it was when new.

The Teg70 had slight hiss on both channels for a short while after power up but recently one channel caught fire so I don't use it any more

I believe that besides repairing the dead channel the hiss and muddied sound would indicate that both amps are due for some capacitors to be renewed ?? Would there be any particular types of caps that you guys would recommend replacing (e.g. electrolytics) or just all of them ? Should I be looking at any other components or the big capacitors in the psu section?

Thanks for bearing with me so far

As far as the dead channel in the Teg70 is concerned, there are a number of cooked resistors that I can clearly see. I figure that maybe a diode failed or a component within the psu if there are twin psu outputs to power the amp channels (not sure yet). I've negligible experience of this kind of repair but have picked one or two things over the years (I'm a computer software/hardware technician).

I'd welcome tips for things I should be looking for (or being careful about).

Thanks guys!
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Old 23rd August 2010, 04:21 PM   #2
Mooly is offline Mooly  United Kingdom
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Fault finding has to be logical.

The integra... does the hiss depend or alter depending on what input is selected and also on the position of the volume control ?

Forget the Teg70 for now, just concentrate on one amp.

Can you get your hands on some freezer spray ? that may help if used sparingly and just "dripped" onto suspect parts.

Electroylitics wouldn't be my first suspect for the hiss, could be a small disc ceramic type cap causing this kind of issue.
Can you post any detailed clear shots of the internal PCB's ?
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Old 23rd August 2010, 07:16 PM   #3
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Hey Mooly! Thanks for getting back to me. Just done a few tests and the hiss occurs at power on regardless of the position of listen/source selector.

It takes a few minutes after being switched off before the residual charge dissipates to re-try, but the level of hiss seems to be consistent regardless of the position of the volume selector at power on.

I'll try and get some pics of the pcbs for both amps onto picasa tonight & paste a link. The Teg70 has the same pcb (labelled Integra) but missing the pre-amp components which may be useful in quickly identifying the pre & power amp sections of the pcb.

I don't have any freezer spray handy I'm afraid and everything takes a while to get up so far north as I am.

Will add pics link later
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Old 24th August 2010, 06:07 AM   #4
Mooly is offline Mooly  United Kingdom
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So the problem sounds like it's in the power amp section as the hiss is constant at all settings.

These type of faults can be the worst to find sometimes. Might also be worth just gently tapping around the components with it on to see if anything shows up that way. Even a scope wn't help much as it will just show the noise at all points in the power amp due to the action of feedback.

Wait for the piccys
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