I found many Pyramid linear power supplies on "give-away" tables or in the trash barrels at hamfests. #They are a source for building your own linear power supplies. #They appear to have undersized heat sinks for the ratings advertised. Linear power supplies are straight forward to troubleshoot and repair. #I would suggest the following web sites:
KBT DC Supplies (troubleshooting - they also do repairs)
David Metz, WA0AUQ article [Power Supply construction]
This Power supply is regulated Supply (protected for over voltage and for too much current draw) therin lies the problem.. It is in shut down condition. Taking all load off, it is supposed to reset itself, it does not. So seems to me there is something wrong in the shutdown circuit. There are two 14 pin IC"s in there that I have no information on. Not knowing what is inside makes it extremely difficult to troubleshoot. I have many years experience in the tv and radio repair field, but need help on this. I could of course rebuild it and make it a linear supply, but don't wish to do that if, I can find some way to fix it first. Thanks...
B H Mineer
B H -
Your Pyramid power supply uses the popular LM 723 voltage regulator chip (a proven IC and over 25 years since first released). #I am surprised you have not come across this popular IC in the radio/TV repair business
The KBT DC web site has all of the specification sheets on the LM 723 voltage regulator IC as well as the 2N3055 or 2N3771 pass transistors. #I provided the spec sheets - so that they would be available for easy reference
Repair tutorial number 1
Repair tutorial number 2
Pyramid does not answer e-mails and I am not aware of "on-line" schematic sources - other than this one diagram. The Pyramid PS-52KX manual can be found here. #
The KBT web site has over 30 pages of information on the repair of linear power supplies using common IC regulators and pass transistors (e.g. Pyramid, Astron, TrippLite) -- better than a SAMS PhotoFact.
KB7KBT has been able to "walk" many amatuer radio operators with little experience through the repair process. #Just drop kb7kbt an eMail, tell him what you have and what you think might be the problem.
All power supplies need to be sent to KBT postage paid and insured round trip. Repair fees will consist of parts, plus a flat fee of $25. #You can then put their "Life Time Warranty" to work.
This does not answer the above question, but I have a couple of damaged supplies (not Astron) which I ran through the dishwasher after a house fire.
I discovered, and ordered one each regulator board from Astron for their RS20 and RS35 supplies, $20.00 USD each plus a little shipping.
Check the zener in the crowbar circuit.
If it shorted, it would explain all..
B H -
Let us know of your results. #
Too much "off-brand" labeling in equipment these days.
WD7WHQ mentioned to check the 15 volt zener diode (a good idea).
The zener diode monitors the output voltage of the power supply. When the voltage gets to 15 volts, the Zener diode conducts. #This in turn fires the SCR and therefore short circuits the output of the supply. Eventually draws enough current to trip the breaker or "blow" the AC input fuse.
TR: It does not take a lot of the conductive grease to make an adequate transfer material. A thin layer on either one, then assemble.
By the way, this stuff is bad news. Make sure you clean your hands, discarding the paper towel (or whatever you used). Then wash liberally. Dow Heat Sink compound is on the list of "bad things" to be around.
After the transistors are bolted to the heat sink, take a paper towel and wipe off the edges of the transistors to get rid of the excess.