HP 6034A Power Supply EPROM  - Page 1
Forum section: electronics / testgear

author: tube7586
author_rank: Newbie
timestamp: August 03, 2014, 12:57:56 pm
content: Hello Everybody ,I have an old school HP 6034A PSU (60V 10A) ,unfortunately it seems to be has a kernel problem :not booting ,it freezing at power up and all LEDs permanently light .Both 256k RAM chips were already replaced ,so I suspect that the old Mostek ROM has a corrupted firmware content .They have been known become degraded due to old age .So now I am looking for that 64k ROM (U25) ,HP part : 1818-3113 .Of course the HEX data content would be very useful too .Thank you in advance for your help ,AndrasSorry for my English ...

author: nctnico
author_rank: Super Contributor
timestamp: August 03, 2014, 01:13:06 pm
content: I'd check for other problems first. It is very uncommon for EPROMs to lose their contents. What does the troubleshooting tree in the service manual lead to?

author: tube7586
author_rank: Newbie
timestamp: August 03, 2014, 01:51:34 pm
content: Thanks for reply .I have first checked all power supply voltages in the processor and mesh (switching psu) board .No problems were found .The service manual suggests testing CPU and RAM/ROM if all leds come on at power on .Unfortunately I haven't got a signature analyzer like the HP-5006A for proper data/address bus testing .The CPU (TMS9981) clock runs properly at 9.2MHz .I need to check the memory chip select and address buffers ICs as the manual suggested .Here it is the troubleshooting tree from the SM :

author: nctnico
author_rank: Super Contributor
timestamp: August 03, 2014, 01:57:38 pm
content: You can also check a lot using an oscilloscope. Make sure to check the address, data bus and chip select lines for logic levels which are half-way between 0V and 5V or are not toggling at all. How about the reset pin?

author: tube7586
author_rank: Newbie
timestamp: August 03, 2014, 02:37:50 pm
content: I will able to check all address and data bus signals with a good TDS520A scope if had a little free time .The CPU has three reset/interrupt inputs .Its interrupt driver circuit is quite complicated ,consists of at least six TTL logic ICs .An interesting thing happened when I replace 9MHz crystal to 8MHz :the front panel meters shows 0.00 ,and just a few leds remain lights ,but the CPU is still freezing .However it seems to be that the self test runs properly .But when I remove the EPROM from its socket the system remains to the base fault :all leds and meter segments light continuously .

author: tube7586
author_rank: Newbie
timestamp: August 21, 2014, 12:54:51 pm
content: Hi all ,Good news !After carefully check all logic levels around the quite unique reset circuit ,made of some glued discrete TTL chips finally I found it works perfectly .All the RAMs ,the memory drivers and selection ICs already replaced to a NOS one .But my beloved power supply still doesn't work ...So finally I decided order that old Texas CPU from ebay for ca. 15USD .On the day before yesterday the part arrived in a nice Hong Kong Post envelope .At first I replace the CPU quickly ,after mains button pushed on the instument start self test promptly ,and displays 00.0 volts & 0.00 amps as it must be .The volts-amps select button works ,RPG knob works ,so everything is very fine .Before I forgotten ,think it's important : that very old cheap DIP 40 pin socket build by the factory tends to wear ,the contact springs weakened ,besides some heavy oxidations due to approx. 1W CPU dissipation etc.The CPU socket were replaced to a new gold plated precision one (also addeed two 16pin precision socket for the RAMs ) .I taken a picture of the control board with the original (faulty) CPU .Best greetings ,Andras

author: iDevice
author_rank: Regular Contributor
timestamp: August 21, 2014, 09:52:07 pm
content: I guess you were lucky this time.If I were you, I would still dump the ROM.Many Mostek's of this era are dead today, I have a few of them in a tray. (Many of them coming from all the Tek 468's I restored.)So when the ROM will fail, you will be able to program the 27CXX EPROM to replace it. (You will need to make a 28>24pin adapter of course)