Programmable version of the TTi PL series Power Supply - Page 1
Forum section: electronics / repair

author: EHT
author_rank: Frequent Contributor
timestamp: January 25, 2022, 09:29:34 pm
content: Hi All,I'm after the service manual / schematic for the *Programmable* version of the classic TTi PL series PSU. The normal versions are PL330QMD, PL330QMT etc., the GPIB ones are PL330DP, PL330TP. The manual for the non programmable version is easily found, e.g.here, but this manual says:QuoteI can find the instructions but not svc / schematic. I guess they are quite rare items? Maybe got superseded by their other ranges quickly?

author: Swake
author_rank: Frequent Contributor
timestamp: November 09, 2023, 11:11:14 pm
content: Hi,Have you found any service or repair information about the GPIB/RS232 interface itself?Got a triple output PL330TP. The third output works perfectly well as long as it is not connected to the communications board. As soon as it is connected the output stays at 0V. As if it is controlled remotely. The setting of the local/remote button does not change anything this.

author: watchmaker
author_rank: Unknown
timestamp: November 10, 2023, 02:33:33 pm
content: Attached. TSX maybe it will help.Regards,Dewey

author: Swake
author_rank: Frequent Contributor
timestamp: November 10, 2023, 04:12:30 pm
content: Thanks for this manual.It does not match completely but there are quite some similarities. The controller and V/A displays for the power supply modules have very similar schematics. There is a PIC16C55XT and in the schematics that you provided the pins 6 to 8 are referenced to talk to the communications board. They call it an 'Inter-Processor-Interface'.My communications board has a Z80 CPU too but that is about where the similarity ends. However, I think that the 'Inter-Processor-Interface' will be setup in a similar way and that will help understanding how things work and hopefully debug it.Btw, just found a half-dead capacitor on the CPU power supply for the second channel. The channel was always acting up on startup for a couple of minutes, then it was working fine as if nothing happened. I finally decided to dig into it with a scope today and found the +5V to have more ripple than seemed healthy, after a few minutes the ripple mostly disappeared.

author: Andy Watson
author_rank: Super Contributor
timestamp: November 10, 2023, 10:53:56 pm
content: Don't know if this will be of any help, but:A while ago i reverse-engineered the GPIB interface for a PL320. This was single-output power supply, however, the GPIB appears to have been designed for two channels.The GPIB module appears to be very much an after-thought - almost a prototype in construction. There were two PCBs to the GPIB module; a processor board with the actual GPIB, and an interface board which opto-isolated serial signals from the processor and provided DACs for the voltage setting.The interface board uses CMOS switches (4066) to switch between local and remote control. My guess would be that one of these switches is defunct.My attempt at reversing the schematic is below:I never got the GPIB working. The EPROM had suffered extreme bit-rot - it was mostly FFh and obviusly not a program of any sortEdit: P.S. I was bemused by the extra, redundent connections on the processor PCB, and some odd cut-outs which were also unecessary in the PL320. Sometime later I discovered that TTi had borrowed the processor board from their 1905A multimeter GPIB - hence the redundent features!

author: Swake
author_rank: Frequent Contributor
timestamp: November 12, 2023, 09:50:59 am
content: Thanks Andy, interesting information.Having experience with only one of the power supplies it is very clear this thing evolved over time. First a power section only, likely with analog meters. Then the digital readout was added based on a PIC. Using a µC was smart actually as using a separate AD was the only way to go to have 4 full digits in the readout and allowed for evolution afterwards such as with the numerical keyboard. I believe cheap of the shelf chips only offered 3.5 digits at the time. After that a communications board was added, I understand in 2 distinct phases and likely by 2 other engineers judging first a 6502 CPU and then a Z80 was used.They where also very cost conscious and used relatively good quality components with all widely available stuff and a somewhat modular setup. Need 1 more amp? Just sandwich another heatsink with power transistor on top of the previous one. Need 2 PS? Well... put 2 in a wider box. Mine is a 3 channel version and it has 3 of everything including 3 transformers and 3 sets of heatsink.You know what thesedon'thave?? A fan! And that my dear friend is a blessing to the ears andthereason I keep it on the workbench.

author: voltsandjolts
author_rank: Unknown
timestamp: November 12, 2023, 04:07:46 pm
content: TTi PL series are great units.PL-P service manual has GPIB schematic on second last page, but I'm sure there are a few revisions in this series so may not be exactly what you have.

author: Swake
author_rank: Frequent Contributor
timestamp: November 12, 2023, 04:53:42 pm
content: YesThat is the service manual I needed, thank you very much