Author Topic: Ahlborn H5 voice issue  (Read 5603 times)

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FYG71

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Ahlborn H5 voice issue
« on: April 05, 2016, 05:54:28 PM »
Hello
I recently acquired an Ahlborn H5 one manual organ (1994 vintage) which has a curious fault.  Although a one manual organ, the stop voices are drawn from 3 chips and circuits from the digital processor board.  The stops from chip 1 all speak without issue.  Those from chip 2 all speak with harmonic distortion and those from chip 3 are barely inaudible.  I have completed a factory re-set but this hasn't cured the problem.  I also checked the on-board battery for leakage (a common problem apparently, which destroys the processor board) but this is intact. 

The distorted stops and those which are silent also behave in this way when heard through the external outputs and headphones and so I think the problem lies in the processor board rather than in the power amplifier side. 

Has anyone experienced this issue before who might be able to give some advice?  I have a copy of the schematic and some electronics experience in terms of replacing components.  It seems a shame to not try to fix this instrument as the rest is in good order.

I did have to replace the main capacitors on the power board as one had shorted out and also noted that the mains plug wiring had a very loose earth connection!  All fixed now.

David Pinnegar

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Re: Ahlborn H5 voice issue
« Reply #1 on: April 07, 2016, 09:33:38 AM »
Hi! WELCOME!

I had hoped that someone else would jump in.

I've got some Ahlborn extension modules and am very depressed by your report of what the batteries can do. Is it irreversible?

Yours sounds a very strange fault. Have you gone around with an amp connected through a capacitor and small resistor as a test probe to hear what's coming out of each chip?

Best wishes

David P
David Pinnegar, BSc ARCS

dragonser

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Re: Ahlborn H5 voice issue
« Reply #2 on: April 07, 2016, 11:00:27 AM »
Hi,
I'm guessing that maybe one of the chips associated with the troublesome voice channels may have failed, or partly failed. If the chips are in sockets than changing them should be easy, otherwise you do need to be careful about changing them ....
If the backup battery batteries are nicad then they are known for leaking in a wide range of Musical equipment.
I have seen a mod done to replace the battery, and then connect the battery using flexible wires to keep it away from the circuit board and then have it placed in a plastic bag, so if it does leak it doesn't damage the circuit board.
It would be worth inspecting around any batteries and seeing if you can see any signs of corrosion
regards Peter B

FYG71

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Re: Ahlborn H5 voice issue
« Reply #3 on: April 07, 2016, 12:44:24 PM »
Thanks for the answers.  The battery does not seem to have leaked at all, in fact, the processor board looks very clean.  The chips are in sockets and so could probably be removed and replaced, presuming that replacements could be sourced (I understand that spare parts are no longer available for this model from Ahlborn uk, don't know if this includes chips as well?)

I haven't probed anything as yet.  I did wonder whether the preamp side of the amplifier board might cause such symptoms?  The headphone and line out circuits appear to lead off after each line out for each division has passed through op amp chips of their own, which seem to then link together.

David Pinnegar

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Re: Ahlborn H5 voice issue
« Reply #4 on: April 07, 2016, 06:13:59 PM »
Sometimes chips in sockets can benefit by being gently lifted, not fully out but lifted and put back in.

Best wishes

David P
David Pinnegar, BSc ARCS

revtonynewnham

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Re: Ahlborn H5 voice issue
« Reply #5 on: April 08, 2016, 09:15:35 AM »
Hi

Be aware that some chips can be damaged by static discharge from your fingers if handled.  Only touch the plastic housing - or wear an earthed aanti-static bracelet.  I have a plastic tool for removing 8 pin IC's - not sure if they're still available, or even really needed.  Good luck.

Every Blessing

Tony

FYG71

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Re: Ahlborn H5 voice issue
« Reply #6 on: April 08, 2016, 09:26:08 AM »
Worth a try to see if there are any poor connections.  I also have a chip lifting tool but it may be too small for larger ones. 
There was a fair amount of fluff inside the organ, mostly the same colour as a fabric cover that someone had lovingly made. 
Everything else functions perfectly on the organ.  It is such a pity that some of the tone generation is affected.  I had wondered if there was a simple way of checking the output signal with a different amplifier by tapping in to the output pins from the board just to check that the fault definitely lives on the generator side rather than the power amp board (where I found a failed and a blown capacitor (both replaced now).

Thanks for all the helpful comment so far.  :)

revtonynewnham

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Re: Ahlborn H5 voice issue
« Reply #7 on: April 09, 2016, 09:17:36 AM »
Hi

A small amp with a proble (signal tracer) or an oscilloscope will enable you to trace the signal.  Is the audio section common to all voices?  If it is, the fault must lie elsewhere (i.e. generators etc.)  Fault finding is applied logic.

Every Blessing

Tony

FYG71

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Re: Ahlborn H5 voice issue
« Reply #8 on: April 09, 2016, 02:52:06 PM »
The fault isn't common to all voices, only those from the respective chip sets.  I am going to try an oscilloscope to see if I can trace where the fault begins in the circuit.  The outputs do eventually merge into a 3 channel system but not before going through preamp stages.

revtonynewnham

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Re: Ahlborn H5 voice issue
« Reply #9 on: April 10, 2016, 08:59:19 AM »
Hi

In that case, I'd start at the inout connections to the pre-amp - if the faullt is apparent there, then it's the generators that are at fault, if it' not, it's the pre-amps onwards.  Do check for the obvious - power rail voltages present & correct and so on before getting too involved though.

Good luck

Every Blessing

Tony

FYG71

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Re: Ahlborn H5 voice issue
« Reply #10 on: April 11, 2016, 06:31:03 PM »
Thanks for all the helpful advice so far.  Sadly, work commitments call again this week but I hope to investigate further at the weekend.

Will update when I have some results...hopefully of a positive nature! ;D

Cheers

Donald

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Re: Ahlborn H5 voice issue
« Reply #11 on: August 03, 2018, 07:58:41 AM »
Hello,
New member here but thought I should respond to this old thread.
In South West Scotland at a local Church about to be closed there is an Ahlborn H5-B (991047 - date code?) with considerable battery acid trouble on the digital processor board, everything else seems ok. The damage has even gone through the feed-through holes and corroded the underside of the board.
From this, I doubt even the most patient of repairs would be reliable as the fibreglass board itself is surely impregnated, however there may be IC and components worth salvaging.
Unless there's a supply of new digital boards, I can't see this one escaping the dump. :(
It is truly appalling design to stick a dirty battery in the middle of a high density microprocessor when with all the room inside the organ it could so easily have been mounted off-board.
Is there anyone desperate and in need of an "organ donor"?
Or have others succeeded in repairing acid damage?
Give me real pipes any day!!
Best wishes,
Donald.

Donald

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Re: Ahlborn H5 voice issue
« Reply #12 on: August 04, 2018, 11:01:12 AM »
As a follow-up, and having heard back from Ahlborn agent in the UK, confirmed - once the acid seeps through the vias or feed-through-plated holes, then the glass fibre has become impregnated, and with it being a multi-layer board (2 trace layers sandwiched inside as well as component and solder sides) EVEN IF a repair worked, it would not be reliable.
The batteries in question have about a 6-7 year life span and OUGHT to have been a dealer recall with design modification to remove the battery from the board and relocate at some distance.
Very sad, and doubtless fairly expensive for a small rural Church at the time, this size of instrument would have been ideal for donation to retirement/care homes, but unless design engineers take into consideration a single life-limiting component, the entire brand name will suffer.
I gather it stopped working about 10 years ago (made in 1999 I think) so not good value.
Otherwise with battery intervention, it would still be good as new and could doubtless last may years.
Replacement boards are not available, so it is terminal.
Ahlborn agent did offer to examine board free of charge to see if it was repairable but mine is considerably damaged all the way through.

Thank-you for a most interesting forum chaps.
Regards,
D.

David Pinnegar

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Re: Ahlborn H5 voice issue
« Reply #13 on: August 12, 2018, 10:18:05 AM »
Thanks for this update

I have Ahlborn expansion modules which have gone the same way :-(

Best wishes

David P
David Pinnegar, BSc ARCS

 


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