22-10-2023, 10:20 AM
(This post was last modified: 22-10-2023, 10:28 AM by peter scott.)
Last week I took a trip by car to the Netherlands and Germany. The main reason for taking the car was to let me carry a very heavy Hewlett-Packard desktop scientific calculator.
I have spent many months trying to repair my HP 9100A without success but from contact on another forum I had a very generous offer from Roland Langfeld who is one of the enthusiasts running https://www.technikum29.de/en/
in Kelkheim near Frankfurt. Roland has a fully working HP 9100A and offered to do board swaps with me.
The HP9100A service manual gives schematics etc for the display and power supply but virtually no information on the actual computer hardware.
This trip also gave me the opportunity to visit Jac in Eindhoven and Jürgen Valter in Aachen. Both have wonderful collections of televisions and radios that they have restored.
I'm very happy to report that on the 5th board to be swapped my HP 9100A sprang into life and after the tedious process of testing about 160 transistors used as JK flip-flops we identified one with a CE short. I had some time ago thought that I had tested all the semiconductors but only using a diode test to show two back to back diodes and not CE.
My next visit was to Jürgen in Aachen. He has a very wonderful collection of early broadcast receivers and also pre-war televisions. In the latter category is a very impressive HMV 902. Strangely the screen image appears bigger when standing in front of the set than it does in photographs.
Jürgen also has a fully working Baird Televisor that he recreated whilst only possessing the correct motor and sync wheels.
My next visit was to Jac in Eindhoven. Jac's television restorations are second to none in quality and as an ex-Philips employee he has many beautiful examples of that brand. His pre-war EMI collection is also very impressive. This was the second time that I had visited Jac and I was keen to see his Philips SX861A operating on the Philips 567 line standard from the 1940s. It gives a very crisply defined picture but uses a plain ground glass screen rather than the later Fresnel plastic screens so light distribution is more centre weighted.
On arriving back home I was very disappointed to find that HP 9100A was no longer working. The display was blank although when switching off it showed a momentary horizontal line at the bottom of the screen. I had been fearful throughout the trip that I might damage the CRT deflection plates in transit so that was my first horrible thought but on emailing Roland he suggested a very simple test. In addition to the CRT there is an error lamp and this should light if you do something like divide by zero. Much to my relief the lamp didn't light so if I only had one fault then it was not in the CRT. Sure enough on checking a couple of transistors that I had removed for test in the museum in Kelkheim one had the base disconnected and resoldering restored my machine to life. Roland didn't have a solder sucker so I had just tacked the removed components back on with the intent of clearing their holes and soldering properly back home.
Peter.
I have spent many months trying to repair my HP 9100A without success but from contact on another forum I had a very generous offer from Roland Langfeld who is one of the enthusiasts running https://www.technikum29.de/en/
in Kelkheim near Frankfurt. Roland has a fully working HP 9100A and offered to do board swaps with me.
The HP9100A service manual gives schematics etc for the display and power supply but virtually no information on the actual computer hardware.
This trip also gave me the opportunity to visit Jac in Eindhoven and Jürgen Valter in Aachen. Both have wonderful collections of televisions and radios that they have restored.
I'm very happy to report that on the 5th board to be swapped my HP 9100A sprang into life and after the tedious process of testing about 160 transistors used as JK flip-flops we identified one with a CE short. I had some time ago thought that I had tested all the semiconductors but only using a diode test to show two back to back diodes and not CE.
My next visit was to Jürgen in Aachen. He has a very wonderful collection of early broadcast receivers and also pre-war televisions. In the latter category is a very impressive HMV 902. Strangely the screen image appears bigger when standing in front of the set than it does in photographs.
Jürgen also has a fully working Baird Televisor that he recreated whilst only possessing the correct motor and sync wheels.
My next visit was to Jac in Eindhoven. Jac's television restorations are second to none in quality and as an ex-Philips employee he has many beautiful examples of that brand. His pre-war EMI collection is also very impressive. This was the second time that I had visited Jac and I was keen to see his Philips SX861A operating on the Philips 567 line standard from the 1940s. It gives a very crisply defined picture but uses a plain ground glass screen rather than the later Fresnel plastic screens so light distribution is more centre weighted.
On arriving back home I was very disappointed to find that HP 9100A was no longer working. The display was blank although when switching off it showed a momentary horizontal line at the bottom of the screen. I had been fearful throughout the trip that I might damage the CRT deflection plates in transit so that was my first horrible thought but on emailing Roland he suggested a very simple test. In addition to the CRT there is an error lamp and this should light if you do something like divide by zero. Much to my relief the lamp didn't light so if I only had one fault then it was not in the CRT. Sure enough on checking a couple of transistors that I had removed for test in the museum in Kelkheim one had the base disconnected and resoldering restored my machine to life. Roland didn't have a solder sucker so I had just tacked the removed components back on with the intent of clearing their holes and soldering properly back home.
Peter.
![[Image: hewlett-packard-hp-65-1974_9vzr.jpg]](https://sm.pcmag.com/pcmag_uk/photo/h/hewlett-pa/hewlett-packard-hp-65-1974_9vzr.jpg)
