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Old 15th December 2010, 03:02 AM   #11
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I should have said that Q9070 which is IFR730 is sorted. I had to pull the heatsink that its' mounted on to remove it. On the same sink are two K626 (2SK626) they are fine. I had read somewhere to replace the IFR730 with the MTP6N55 or N60 as a field service mod. Anyone have experance with this SMPS?
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Old 15th December 2010, 04:12 AM   #12
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I have a service manual for the 2215, circa 1982. Since they made the 2220, 2230, and 2430 in the same year 1986. They might have kept the same power supply for the first couple years before they changed it. Maaaybe....
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Last edited by blakktalon; 15th December 2010 at 04:24 AM.
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Old 17th December 2010, 02:39 AM   #13
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The 2220, 2221, and 2230 used a common power supply. The circuit is very similar to the non storage 2213, 2215, 2235, and 2236 etc. but has been beefed up quite a bit to deal with the extra load of the storage board.

I've scanned the power supply page, the waveform photos, and the theory of operation from my 2221 manual. Can you receive a 3M email?

The part that is shorted is in the preregulator part of the power supply. The power supply has a single ended flyback 43 volt pre-regulator and a push pull inverter that drives the main transformer.

I'm trying to remember this circuit... It's been close to 20 years since I've worked on the 2200 series. IIRC, when the fet was shorted other parts to check were the 1uf film cap C907, the diodes CR906 and CR907, Q908, R909, CR908 and R908. Sometimes the regulator controller was taken out also, but it's a common part (TL594) that is still available.

The crowbar protection circuit also needs to be checked. Q935, VR935, R934 all need to be checked out. The crowbar fires if the output of the 43 volt regulator goes over 51 volts and shorts out the supply and blows the fuse.

Keep in mind if you want to be able to probe around in the preregulator circuit you must have an isolation transformer.
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Old 17th December 2010, 03:11 AM   #14
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Gary,
Thanks’ that is the most comprehensive description I have received on the supply and associated circuit. The very simple white paper I found lists some of those parts but not all. Thank you for that. I have a question if you remember concerning the replacement the IFR730/ Q9070. The white paper said to change that to a MTP6N55 or 60. I remember someone using one of them on a Gain Clone at one time. I have not been able to find that part only the original IRF730. Do you know where I may be able to find a few? I found some at Nebraska Surplus but who knows if they are still good after extensive/incorrect handling and also the k626 which I can cross to a BUZ350. From what I understand this was an ongoing problem with the 22XX series. The power supply from what I can understand had marginal parts selected in some areas. There was some mention of a “P/S MOD-KIT” but I cannot find any information concerning this other than one is spoken of. I have the service manual now but nothing is listed to that effect.
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Old 19th December 2010, 04:58 PM   #15
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A couple of questions-

What is the serial number of your 2220 scope? The mod kit applies to 2220 units between B010100 and B020491. Units that have serial numbers above this range already have the updates in place. Also if the mod kit was installed on a low serial number unit there will be an extra sticker on the back of the scope that states mod kit 050-2239-03 has been installed.

Have you found the circuit description in your manual? In the 2221 manual it is section 3-7. This will give you a very in depth description of what is going on.

I think that a good replacement for Q9070 would be the IRF830 MOSFET that is available from Mouser for a couple of bucks. This MOSFET has similar drive requirements to the IRF730 and handles higher voltage.

One mandatory mod was to cut off the molex connector connecting to Q9070 and solder the wires directly to Q9070. Over time the leads of the MOSFET would corrode then overheat causing failure.

Some more info (that may be redundant to what you already have) is available at tektronix 2235 , blown switchmode

Keep us informed on your progress.
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Old 19th December 2010, 06:00 PM   #16
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The serial number of the scope is "B020108" which falls into the lower unit group. I have no history on the scope as I just reived it. The unit has been worked on before and there is some minor damage from the last attempt to service. There is a trim pot broken on the main board and a few wires broken, minor detailes. The molex for Q9070 is in good shape but I will wire direct to Q9070 when I replace it. I checked on the Sphere web site and there is no listing for the mod kit at this time. Do you now where I could locate the kit or find the description of the parts for this kit. I have checked the P/S caps and all will need to be replaced. Everyting in the crowbar circuit is fine also. This scope is my backup to my analog 2236. I realy can not go with out a backup and the storage on the 2220 is still nice to have. I am giving away my Tenma backup scope I have now on this site to someone in the next week or so. I would like to get this one up before she go's if posible. Thanks' for your help.
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Old 19th December 2010, 10:09 PM   #17
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I doubt that you will find a mod kit. I do have a .pdf of the mod kit instructions. The documentation includes a list of of all the parts that get changed and how to do it. It's pretty involved but not real difficult for someone experienced in repair work on circuit boards. Tek did a great job of documentation.

Send me an email via the forum and I'll send the mod kit pdf to you. I can't do attachments in the forum email system.
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Old 22nd December 2010, 10:17 PM   #18
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I sent Gary a "PM" but he must be buzy with the Christmas rush. I also spoke to Sphere research today and they belive they have the parts to the kit but not by kit number. They need all the Tek numbers to make up the kit for me. I also still need a accurate manual for this powere supply. The 2232 I have is for sure not the same as the 2220. I found a link for the 2215 but the "RAR" files have a bad "CRC" error. I find that some were built without the pre regulator built on the board, more versions than a "Beatles" song. So, Gary if you get a chance I have sent you a "PM" with my email address to send what you have.
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Old 19th June 2012, 12:42 PM   #19
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Hi Folks, I have just bought a scope ..... with a PSU fault .... it's the 2220 and appears to have blown the prereg FET (according to the seller).

He is pointing me to a 2232 model service manual - will that be close enough to the same circuit as mine or would I be wasting my time?

Is the scope worth fixing anyway? Is it any good for LF / Audio and general faultfinding purposes?

Any thoughts gratefully received
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