Re: Tektronix 2230 Oscilloscope failure
From: Jim Yanik (jyanik_at_abuse.gov.)
Date: 11/01/04
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Date: 1 Nov 2004 01:53:08 GMT
Gary Morton <gary@alma.demon.co.uk> wrote in
news:oBehd.3620$up1.3119@text.news.blueyonder.co.uk:
> My 2230 scope suddenly died the other day.
>
> It's a great piece of equipment and I would like to repair it (if
> possible) or
> pay for it to be repaired if economically viable. I have a contact
> in the TV
> repair trade who may be able to help (he repairs switcher PSUs
> regularly).
>
> Does anyone know of any companies in the UK which specialise in the
> repair of Tek scopes?
>
> I'm pretty certain that the PSU has blown. The fuse blew and and the
> unit blows replacement fuses. The fan doesn't come on and the front
> power LED doesn't come on.
>
> I opened up the scope and it appears that the PSU is part of the large
> bottom PCB. It appears to be well connected to the front panel. It
> looks like you have to know what you are doing to safely extract the
> PCB to even examine the PSU area. Any suggestions are welcome.
First,you don't extract the main board to service the PS.(a major PITA)
You can remove the PS shield(cage) and bottom cover and work on it
(unsolder) from the bottom. The problem is most likely to be bad
electrolytics (ESR),shorted rectifier diodes,and/or the pre-reg FET(on a
small heat sink) is probably shorted. The FET should be soldered to the 3-
wire ribbon cable,its Molex connector should have been removed by a field
mod when serviced(at TEK).Other failures could be the power oscillator
transistors(shorted or open,along with their base resistors,or the pre-reg
overvoltage crowbar;a bad 51v zener,open 3 ohm fusible R,or shorted SCR.
A less likely possibility is a bad HV multiplier.
>
> Which other Tek scopes share the same PSU design?
2213,2215,2235,2236,same general architecture.Components may be labelled
differently. 2230,2235/36 have higher anode V,IIRC.
>
> I have already googled for "2230 repair" but it might be helpful to
> try for similar faults on related scopes.
>
> regards...
>
> --Gary
>
>
The 2230 uses a pre-regulator based on a TL494 or TL594 IC to knock
rectified line V (90-250 VAC input) down to ~43vDC, to a power oscillator
that creates the secondary low voltages and the HV cathode and anode
supplies.
You must use an isolation XFMR to scope the primary side of the PS.
Incidentally,this scope PCB was stuffed on an automated insertion
machine,wave soldered,and sliced into pieces,the front panel PCB remaining
attached to the main board.
-- Jim Yanik jyanik-at-kua.net
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