Mark 8 Amp

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seann1974
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Joined: Wed Nov 11, 2020 11:59 pm

Mark 8 Amp

Post by seann1974 » Thu Nov 12, 2020 8:34 pm

I recently acquired one of these apps. The internal T1 fuses are blown. Both of them. I found the schematic for this amp as well. I tested all the power transistors and they seem to be fine. I found a post about the same issue and it being the rectifier diodes in the power supply. I'm curious admit the capacitors that are part of that circuit. Would it be wise to replace them as well? Also, does anyone recommend a place to get the replacement components.

So far I have found the rectifier diodes are 1N4003 and 1N4148? And the Zeners are 1N4744? Anyone familiar with the capacitors? I brokee the one on the rectifier bridge between CR136 and CR135.

My dad was an electronics repair guy there at Peavy in Meridian a few years back. I appreciate the help.

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Enzo
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Re: Mark 8 Amp

Post by Enzo » Fri Nov 13, 2020 8:45 pm

You can get components from Peavey, or I often use Mouser for general parts.

Power transistors would not affect those fuses.

The fuses serve the low voltage supplies. DO the fuses blow with the preamp board cable disconnected? On the supply board itself, the cap between the fuses could be shorted, a rectifier diode could be shorted. ANy one of the filter caps could be shorted, a voltage regulator could be shorted. For that matter one of your op amps could be shorted.

seann1974
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Re: Mark 8 Amp

Post by seann1974 » Sat Nov 14, 2020 11:35 pm

So I did some testing in the board. I found CR101 and C100 are both shorted as well as CR124 and C118. All rectifier diodes seem fine.

I ordered replacement parts for the ones I found bad. I don't have a tester to check the OP Amps or how I to get the replacements from Peavey.

Once I can replace the faulty components, I'll report back to what happens after I replace the fuses and power it up.

seann1974
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Joined: Wed Nov 11, 2020 11:59 pm

Re: Mark 8 Amp

Post by seann1974 » Wed Nov 18, 2020 10:19 pm

Those 2 zeners were the issue. I replaced the caps too, even though they tested fine. Amp sounds good. Now I just need to figure out what all the dials and inputs and buttons do. Lol

I appreciate the guidance Enzo.

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