Building Mark Levinson 38 preamp chassis from scratch

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#261
Hello Willcycle,
A man after my own heart. Audio + cycling! I had a nice 100-mile ride from my house to the NC mountains Saturday morning followed by capacitor replacement on the 36 Saturday afternoon.
Did you do any parts upgrades on your 380S or was it more for preventive maintenance? On my 36 I am doing a lot of the parts upgrades that have been suggested in this thread.

Thanks!
 
#262
My unit was damaged by lightning so I had to rebuild the power supplies so while I was in there I performed a complete recap. I stayed with stock values using 105 deg Nichicon caps for a long service life.

A century ride this far in to cold weather season is impressive. With the unusually warm weather we had here in MD I go out three days in a row for my usual 28 mile loop. For winter training I just bought a nice spin bike to help keep me fit for next spring. Once the temperature drops to the 40 - 45 deg. range my hands and feet get too cold. One of the symptoms of getting older.
 
#263
We had crazy warm weather this past week. I did a charity ride yesterday in shorts and short sleeves. I have found that the warmer that I keep my core, the less problem I have with hands and feet. In the 30s I use a Craft base layer, winter jersey, vest, and another jersey on top.

Sorry to hear about the lightning damage. I was shocked to see how many of the Nichicon caps were leaking in my old No.36. Some of them were working on the traces under the cap and had already eaten the solder mask off of the board. I cleaned it up and sealed the traces with clear lacquer. I swapped those caps with long-life (5000-hour) high frequency, Panasonic FR caps. Some of the UC 68uf caps were also leaking but didn't cause any pcb damage.
 
#265
Hi All, resurrecting an older thread, but I have a no380 preamp and have had distortion on the right channel after a 1 day power down.
Now I have DC on the right channel, causing my 331 Power Amp to shut down.

Many of the 100uf nichicons appear to have leaked and some of the op-amps look a bit wet.

I presume this may be the cause of my woes?

Any advice appreciated.
 
#270
Hello, I found one Agilent HEDS-5701-C00(100cpr) from eBay. I found it working, but is too slow for my M38S. I found some pictures of M380S and it had C12. I think ML have changed the encoder and the chip in some point. I think ML38 and ML38S have G12 or other much faster type. I am planning to try HEDM-5500-G12. The ML380SL seems to have yet new type... this is very difficult part to find. Last night I ordered parts for front panel interface from Mouser. I hope this helps out.
 
#274
The preamplifier #38 was not controlled from the buttons on the front panel, and the display flashed dots chaotically. The input and output control relays are always clicked. I did not have a circuit and I knew exactly which i/c for which answer. I suspected U2001 (MC68HC11A1FN) and ordered through M.L. dealer. When the chip(MC68HC11A1FN) came and I replaced the faulty?, The amplifier did not work, but behaved completely differently.
 
#275
I found an electrical circuit and, according to the scheme, I began to look for the cause of the malfunction. The chips of the U2203 and U2205 M.L. interface were dead. These chips have been replaced. Preamp started to turn on the network button, pass the test and then display it on the "new E.E." display. The i/c of the UV EPROM I checked for compliance with the checksum indicated on its body. The control sum coincided.
 
#278
I already have the control board, now I need to get the rest - can someone help?
 

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