Phase Linear 4000 power supply question
I just started to repair the power supply of my PL4000 [series , S/N 4P 18241] but ran in to some documentation problems and i was pointed to this very interesting forum.
Looking at the schematics of the PL4000 I don't find a very good match with what I am working on. They are from the service manual I found links for on several sites including here, diyAudio. It is named "hfe phase linear 4000 service" weighs in at 12Megs and comprises around 17 schematics and a exhaustive step by step diagnosis/repair guide.
Neither of the "Mother Board" diagrams III-2 or III-4 seems to match up with what's in my chassis. The "Interconnect schematic" dated oct-73 comes closer but shows next to the transformer a Q1 = 2N3055 power transistor while on our board we find two 8 pin DIP voltage regulators: UA78mg & UA79mg vtage regulators which i cant trace in the documents.
The power LED lights and there is about 25 volts across the secondary of the transformer (unloaded). Checking the output of the regulator section shows only a volt or less both plus and minus.
Any experience with this supply? Are there more revision of this unit than are generally talked about? Is it easy to source these old DIP pak UA78/79MG regulators? Or are there recommended substitutes? And should we swap in a new transformer?
Any advice would be greatly appreciated.
W. J. Ryan
I just started to repair the power supply of my PL4000 [series , S/N 4P 18241] but ran in to some documentation problems and i was pointed to this very interesting forum.
Looking at the schematics of the PL4000 I don't find a very good match with what I am working on. They are from the service manual I found links for on several sites including here, diyAudio. It is named "hfe phase linear 4000 service" weighs in at 12Megs and comprises around 17 schematics and a exhaustive step by step diagnosis/repair guide.
Neither of the "Mother Board" diagrams III-2 or III-4 seems to match up with what's in my chassis. The "Interconnect schematic" dated oct-73 comes closer but shows next to the transformer a Q1 = 2N3055 power transistor while on our board we find two 8 pin DIP voltage regulators: UA78mg & UA79mg vtage regulators which i cant trace in the documents.
The power LED lights and there is about 25 volts across the secondary of the transformer (unloaded). Checking the output of the regulator section shows only a volt or less both plus and minus.
Any experience with this supply? Are there more revision of this unit than are generally talked about? Is it easy to source these old DIP pak UA78/79MG regulators? Or are there recommended substitutes? And should we swap in a new transformer?
Any advice would be greatly appreciated.
W. J. Ryan
I cannot find anything save a diagramme for a Model 4000 manufactured in Linwood, Washington DC. This uses a 2N3055 and various regulators. It has the MC1312 Quadraphonic decoder built in with a four channel power amplifier.
Is this your machine?
Is this your machine?
Dear Jon,
Yes, definitely from Linwood Washington (the state) but not exactly.
I have the "series two" version of PL4000 from which the quad decoder was deleted
(not much quad material in mid 70s). And no power amp is included. I'm using a GAS Son of Ampzilla which is still in great shape.
After looking around again last night I'm beginning to wonder if it's really worth restoring. Except for its special effects, it's not very well regarded.
WJ Ryan Amsterdam
Yes, definitely from Linwood Washington (the state) but not exactly.
I have the "series two" version of PL4000 from which the quad decoder was deleted
(not much quad material in mid 70s). And no power amp is included. I'm using a GAS Son of Ampzilla which is still in great shape.
After looking around again last night I'm beginning to wonder if it's really worth restoring. Except for its special effects, it's not very well regarded.
WJ Ryan Amsterdam
The PL4000 Series II was introduced in the late 1970's, the documentation you have is for the original PL4000. Check at http://thecarversite.com for documentation on your Series II. I had an original PL4000 I owned from 1976 to 2007 and got good service from it with only a few repairs along the way. I generally used it without all of the fancy effects, although the Autocorrelator function was somewhat useful on less than pristine vinyl.
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