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IBMU Repairs


Bob042

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I think that's a sensible way to approach it - power up from a bench PSU and measure the voltages at the test pins. That will at least show if the PSU card is working and you can work on from there.

 

Andy

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Bob

 

Usually when servicing equipment with cards slotted into a cage there is an extender card with a pug one end and socket the other end connected pin to pin, which can be inserted to lift the suspect card above the rest so it can be got at - otherwise you are limited to test connectors along the edge. In the absence of this you have to temporarily solder wires to test pins and reinsert the card.

 

The approach of using a bench PSU is sensible - I think it will also be worth checking that the output of the PSU and the input to the DC-DC converter modules is more or less the same in case something has gone high resistance in the input filters - the converters will work from much lower than 20V so the CPU will still run in such a case, even if there isnt enough voltage to run the battery charger proper.

 

Regards

 

Iain

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Hi Iain,

 

Thanks, I will be trying the input module first before moving onto the cards. My plan is to start on the testing at Easter when I have a decent amount of time. I wish I could get hold of one of the extender cards! but as you say I can easily tack on test wire to the pins which is what I'm going to have to do. I'm convinced there is not a great deal wrong with the IBMU that powers with the vLO fault, its just tracking the fault down. The one that's dead of course is another story but in time I'm sure it can be sorted.

Will update as soon as I can

 

Regards

 

Bob

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  • 3 weeks later...
how did you get on Bob i have the same fault on my new ibmu :embarrassed:

 

Hi Rob?

 

Sorry but never had the chance over Easter to do what was intended.

 

All being well, I will have the time next Saturday with my wife at work to test out the IBMU with the vLO fault. I am currently trying to locate replacement cards, of which I have sourced one, the real problem item for this fault I believe to be the PSU but have yet to prove it.

 

It is frustrating, and I sympathize with you as what happened to you was a re-run of my experience. I have however purchased a third IBMU which is functioning perfectly. In the meantime I will sell? the dead one or keep it for spares? and keep the other once repaired for back up. Not sure yet but IBMU'd out at the moment.

 

Will update this thread shortly.

 

Regards

 

Bob

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afternoon, the below may help.

 

i blew some of the psu capacitors trying to get the thing working, am waiting on a couple of capacitors to get my one going. think its C26 and C14 in the centre of the psu board that are at fault on my unit.

 

Fingers crossed.

 

IBMS preventative maintenance/repairs

 

The main faults with IBMUs are caused by short circuit Tantalum capacitors.

These cause the various power supply rails to go low volts and/or cause the two white modules on the PSU card to fold back.

 

All of the Tantalum capacitors in the IBMU should be treated as suspect!

The following are the most likely areas of failure and these should be changed first:

 

PSU CARD

 

C40, C34 33uF 25V (Part of 12V supply circuit)

 

C26, C14 22uF 16V (Output of +15V & -15V module)

 

ANALOGUE MODULE

 

C1, C5, C8, C9, C12 All 10uF 25V

 

LOGIC MODULE

 

C1 33uF 25V

 

The various voltages can be tested from the test pins on the front of the Analogue Module.

When working on the PSU card I normally power these individually from a current limited 24V laboratory power unit, this makes testing of the individual supply outputs much easier.

 

The PSU card also contains four 22uF 40V Tantalum capacitors, C11, C16, C20 & C38 these do not seem to give any problems, but should be suspected if there is no output on the 12V rail. (22uF 40V Tants are about £12 each so replacement of these could be expensive!) If needed I would use normal electrolytics 125 degree C type in these positions. This would keep the cost to sensible proportions where low ESR would not seem to be a prime requirement.

 

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Hi

 

This is the basic doc I have sourced my info from, I would love to know where it came from! The doc is basically a PM one against a specific repair this if that one, 'replace all listed and you wont have a problem' but I prefer to know what the fault codes are and the "field" repairs for them. Somewhere this info exists outside of Widney.

 

How do you know it's C26 & 14 on the PSU card?

 

Keep us informed, any info on these things is invaluable to us all.

 

Regards

 

Bob

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  • 3 weeks later...

Evening all,

 

im happy to say my IBMU is up and running!!!

 

first thing i did was test the 15v on the test pins and was getting around 2v ish, after reading about C26, C14 22uF 16V (Output of +15V & -15V module) i suspected these may be at fault. now ive replaced them and everything seems to be working.

 

good luck with yours bob but i suspect it could be the same two capacitors that need changing

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Evening all,

 

im happy to say my IBMU is up and running!!!

 

first thing i did was test the 15v on the test pins and was getting around 2v ish, after reading about C26, C14 22uF 16V (Output of +15V & -15V module) i suspected these may be at fault. now ive replaced them and everything seems to be working.

 

good luck with yours bob but i suspect it could be the same two capacitors that need changing

 

That's fantastic news, very pleased for you. So then for VLo fault we should be saying these are the 2 to replace? At the moment I've a little long standing project half finished on the LWT, which will be finished this weekend. IBMU will be the next job which will be the spare to the gwo one installed in the vehicle. I also have plus 2 others (non working) as spares. I may later have a go at these to get them up and running.

Where did you get your tants from?

Regards

Bob

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  • 1 month later...
Any more news on this, out of interest?

 

Andy

 

Hi Andy,

 

On hold at the moment pending the Autumn as all time is being taken up restoring my '57 Narrow Track Sankey.

 

Will resume in due course, thanks for the interest.

 

Regards

 

Bob

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  • 4 years later...

Hello

I have just found this thread on IBMU repairs which is interesting. Having repaired many of these units, most of the comments given above are factual and valid.

The main problem with these units is, as noted by Iain, the Tantalum Capacitors failing Short Circuit. Most problems lie in the Power Supply Card although the Analogue modules frequently cause problems. Faulty Tantalum Caps often appear burnt out and these are easy spotted. Otherwise I would advise the use of a short circuit locator, such as the Polar "Tone Ohm" which will save a lot of time.

The white PSU modules on the PSU card are fairly resilient but will fail if they see a short circuit for long periods. Spares are difficult to obtain but other commercial PSUs can be substituted by drilling new mounting holes in the PCB.

I suggest running the main PSU card from a 24V bench power supply and checking the various voltage outputs. 

I am currently preparing a document that details basic repairs on the IBMU which will be available shortly. I also have a number of PSU cards that have been serviced and fully tested should this be of interest. My location is in Eastbourne.

Barry G8DXU    

 

 

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  • 2 months later...

I have received an email from "Pentecost" regarding the manual that I am preparing on IBMU repairs.

This is well underway but has been slowed down by my work on the Clansman PSU50A repair document.  Members interested in this and the PRC320 can search the http//sars.club website (The Southdown Amateur Radio Society). The document "Clansman PSU50A repair guide" will probably come up in search engines as will the "Clansman PRC320 RT320 repair and servicing" 

These abridged articles will give members an overview of common problems and suggestions for suitable repair solutions.

The IBMU document should be completed in the near future and will probably be published on the SARS site in the first instance.

Barry G8DXU

 

 

Edited by SeaCall
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  • 4 weeks later...

Hi Folks

Just to clear up a question as to the origin of the note entitled " IBMS preventative maintenance/repairs"  as quoted by "Landymad" and "Bob042"

This was one of the early notes made during early investigations at SeaCall Ltd. into faults found in these units. We had acquired a large quantity of non-working IBMS units which were subsequently repaired in our workshop. This note was sent out as an email to assist one or two people several years ago when there was little good info on these items. It appears to have done the rounds and to have been of some assistance!

With complex systems such as the IBMU the fastest way to isolate faults is to swap cards for known good items. But it is acknowledged that amateurs will often not have good spares available. In this case it is suggested that the whole IBMS is initially powered from a current limited laboratory supply set to 24V.  Whilst some of the active components have been know to fail the Tantalum Capacitors are the main source of problems. Wholesale replacement of these normally solves most faults.

It is worth noting that some failures in the PSU card can result in output voltages being much higher than normal. This will tend to exacerbate damage to Tantalum Capacitors and semiconductors in other boards.    

Experience has shown that if one only replaces the capacitors found to be faulty, then supplies will often fail in the near future when other capacitors subsequently fail! 

 As noted in my earlier posts I intend to publish some more comprehensive repair information shortly.

Barry

G8DXU    

Edited by SeaCall
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