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| "John Smith" <invalid@invalid.invalid>: Oct 12 04:00PM -0400 Does anyone have any experience with the Mackie SR24.4 A customer asked if I could repair one which he said had a power issue. So I was hoping for an easy power supply repair but on opening it I find this in channel 11. s651.photobucket.com/user/jbloggs2/library Sorry Mr Customer I don't think it's going to be repairable. |
| Phil Allison <pallison49@gmail.com>: Oct 12 09:18PM -0700 John Smith wrote: > this in channel 11. > s651.photobucket.com/user/jbloggs2/library > Sorry Mr Customer I don't think it's going to be repairable. ** It might take a bit of time and work, but that looks repairable to me. Mackie don't bother to de-couple each channel with fusible resistors in case of a short. Op-amps can be the cause and then PSU delivers up to 20 watts of heat into one - starting a small fire. I would start by removing all the burnt parts and seeing if the PSU fault is cleared. ... Phil |
| "John Smith" <invalid@invalid.invalid>: Oct 13 09:38AM -0400 "Phil Allison" <pallison49@gmail.com> wrote in message news:32bf3ff3-7b1e-4313-83af-eb072da2a5a1@googlegroups.com... > watts of heat into one - starting a small fire. > I would start by removing all the burnt parts and seeing if the PSU fault > is cleared. Yes I probably could repair it by cutting out the burn, bridging the tracks, and remaking the circuit on the back of the board with a DIP version of the opamp (if it's a failed opamp) and the relavant components. However the customer has decided not to go that far and just wants the channel 1-14 board disconnected. |
| Nick de Smith <nick@desmith.net>: Oct 12 10:27AM -0700 > electolytic caps on the B+ > Mark Checked the main reservoir caps - 6800uF @ 25V - ESR was 0R2 @ 100Hz, seems pretty much ok... Nick |
| M Philbrook <jamie_ka1lpa@charter.net>: Oct 12 07:29PM -0400 In article <4c73540d-1249-4ab8-9c09-a21c228a5dc2@googlegroups.com>, nick@desmith.net says... > When its fine (90% of the time) it's an excellend radio cassette... > Bit puzzled as to where to go next... > Thanks sounds like a cap reforming.. Jamie |
| Phil Allison <pallison49@gmail.com>: Oct 12 09:55PM -0700 Nick de Smith wrote: > Checked the main reservoir caps - 6800uF @ 25V > - ESR was 0R2 @ 100Hz, seems pretty much ok... ** That figure would be the cap's impedance at 100Hz. The ESR value is much lower, maybe 0.02 ohms. Most ESR testers use a frequency between 20kHz and 100kHz, where the impedance and ESR values are near the same. .... Phil |
| jurb6006@gmail.com: Oct 12 11:21AM -0700 Sloppy capstan bearings. Look see how they're mounted. Usually there are three screws. If it is not too terribly bad you can rotate the bearings, sometimes that will work, others not. If not, you'll have to push the bushings out and find a machine shop. Actually you'll have to take them the whole thing, they can push them out. Years ago when these things were plentiful it would not be worth doing, but now that they are a rarity it might be. I don't now what a machine shop or machinist would charge, but it is not going to be five bucks. My lathe was bigger and would not hold the tolerance for this, plus I sold it recently. But really, to be fair as a private guy, not a shop I would probably do it for like $30. Shops generally have a per hour figure for each machine, you got a few minutes to cut the stock and not more than an hour lathe time. The way to check this is to try to move the flywheel. It will most likely move in one direction, to and fro in relation to the front of the unit. If you turn the bearings, keep in mind which way the force will be. It is pulling the tape to the right, and it is worn in the back at the top and maybe a little at the bottom. You want ti oriented so that the force does not skew the capstan which will give you even worse problems. Think about which way it was going and the force of the tape, then decide which way to turn it. There is a possibility that due to the mounting arrangement you cannot turn the whole bearing. If this is the case then you have to push out the bushing(s)and just rotate them. Mark EVERYTHING. Also, if the top and bottom are identical, instead or rotating them, keep them in the same position but switch them. We used to scrap units over shit like this, but no more. You can easily get $200 to fix a betamax now. If you can actualy do it that is ... (I just noticed the word "betamax" is marked by my spellheck, how dare they ! I HAVE a betamax !) |
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