Thurlby Thandar PL310 - Page 1
Forum section: electronics / repair

author: alanb
author_rank: Frequent Contributor
timestamp: July 09, 2014, 07:42:25 pm
content: Does any one have a schematic and/or service manual for the above? I am trying to fix a fault with the voltmeter that causes it to show 40.95 regardless of the actual output voltage.I have found a service manual see attached however this does not appear to be for the version that I have. Mine includes a PIC16C55 and dates from about 1991, this chip is not shown on the attached manual.Thanks in advanceAlan

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2014, 07:59:43 pm
content: Based on comments from others here, if you contact TTi they should be able to help you.

author: alanb
author_rank: Frequent Contributor
timestamp: July 09, 2014, 08:03:04 pm
content: Thanks IanB I will contact them in the morning.

author: KJDS
author_rank: Super Contributor
timestamp: July 09, 2014, 08:39:31 pm
content: I think I've got a pile of these in various states of disrepair. I might have a spare voltmeter board, will check on Friday. Can you put up a picture of your board?

author: alanb
author_rank: Frequent Contributor
timestamp: July 09, 2014, 08:57:21 pm
content: Photo attached, sorry about the poor quality.

author: lowimpedance
author_rank: Super Contributor
timestamp: July 09, 2014, 11:02:59 pm
content: I have a PL320QMD which uses the same readout PCB (by the look of it!) and I have the circuit of it.Will have to wait till I can scan it at work tomorrow though.My PL320 had both channels completely blown , with one readout showing the 40 odd volts like yours and the other some random rubbish !.After replacing all the 2n3055 pass transistors the readout that showed 40V now worked , but the other readout was toast. Noted that the A/D converter IC2 was getting rather hot (an ICL7109 ).So long story short, I read the firmware from the good PIC16C55 and copied to a new one and then replaced both the Pic IC1 and the A/D IC2 on the dead display board and bingo it now worked.I can also upload the firmware if needed but I would suspect IC2 first.If KJDS can supply a working display PCB then that would be the easiest solution.

author: alanb
author_rank: Frequent Contributor
timestamp: July 10, 2014, 08:12:15 am
content: Lowimpedance - thanks for the reply, the schematic will be very helpful. I hope the fault is not the ICL7109 as it appears to be the only expensive component on the board, about £20 at RS components. Also the current meter is working am I correct in thinking that this uses the same IC with multiplexing of the input?KJDS - my preference would be to repair my existing board however is that is not possible or is not economically viable I would be interested in a replacement board so please let me know what you have available.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: July 10, 2014, 07:17:18 pm
content: The file is too large to attach here.You'll find it here:http://www.vintage-radio.net/forum/showthread.php?t=107421My experiences with that model are also linked to in that thread.Hope this helps,Mark

author: alanb
author_rank: Frequent Contributor
timestamp: July 10, 2014, 08:04:08 pm
content: Thanks MarkIt looks like the correct schematic.I won't be able to work on this until the middle of next week but when I do I'll report back on my progress.Alan

author: lowimpedance
author_rank: Super Contributor
timestamp: July 11, 2014, 12:11:58 am
content: PDF of service and operator manuals plus PIC16C55 firmware, will need a suitable device programer for that though .Zipped

author: alanb
author_rank: Frequent Contributor
timestamp: July 11, 2014, 07:57:51 am
content: Thank you Lowimpedance

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: July 11, 2014, 09:05:34 am
content: Interesting - I assumed the PIC would have been code-protected, so I didn't bother trying to read mine.

author: IO390
author_rank: Regular Contributor
timestamp: July 11, 2014, 01:09:51 pm
content: Do you still need schematics?I've got the full original service manual for the PL310/PL320 and some other stuff on a disk if you still need it.IO

author: alanb
author_rank: Frequent Contributor
timestamp: July 11, 2014, 01:30:23 pm
content: IO390 - Not needed now as the one from Mark Hennessy appears to be the correct version. Thanks for the offer.You mentioned that you have other stuff on a disk, is that firmware? In Lowimpdance's post he included firmware 'thurlthanPSV2'. I'm hoping not to have to change the PIC but if I do so is yours the same version? In fact does any one know anything about firmware versions? Is it the same across all models PL310/320 etc and are there any revisions for bug fixes or improvements?

author: lowimpedance
author_rank: Super Contributor
timestamp: July 13, 2014, 04:49:09 am
content: Quote from: Mark Hennessy on July 11, 2014, 09:05:34 amIndeed , but much to my relief it was not.My supply was badly damaged by the previous owner, and had required the replacement of both IC1 and 2 on one of the meter PCB's.I suspect there would be not many firmware revisions for just a 'meter' drive circuit. (has no control over the analogue power circuits).

author: alanb
author_rank: Frequent Contributor
timestamp: July 17, 2014, 08:39:22 am
content: I replaced the cd4052 multiplexer last night, unfortunately this did not resolve the problem.It now looks as if the fault is being caused by the PIC16C55. Are there any PIC16F devices that can be used as a direct replacement as my only programming tool is a PICKIT3 and as far as I am aware this won't program PIC16Cxx devices.

author: Andy Watson
author_rank: Super Contributor
timestamp: July 17, 2014, 12:45:52 pm
content: What does the current meter display?

author: alanb
author_rank: Frequent Contributor
timestamp: July 17, 2014, 01:01:53 pm
content: 40.95 on the volts, current meter may show correct reading. I assume that 40.95 is the maximum count (2^12) -1.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: July 17, 2014, 01:05:18 pm
content: Doesn't sound like the PIC to me. A bit of probing around with a 'scope to see the various signals should reassure you of that. A dead PIC wouldn't display any numbers on the multiplexed displays, for example...To be honest, it sounds very similar to the problem I had - which was discussed in the link I posted earlier.

author: Andy Watson
author_rank: Super Contributor
timestamp: July 17, 2014, 01:08:05 pm
content: Quote from: alanb on July 17, 2014, 01:01:53 pmYes, 4095 equates to maximum scale. The point is that the PIC and the DVM chip are common to both volts and current - so if one reading is correct (or just different) it's unlikely to be a fault with either chip. Unless one of the MUX lines on the PIC is defunct. Try shorting the input to the DVM - pins 34 and 35 - the sources are all protected by resistors so it shorting the pins shouldn't damage anything.

author: alanb
author_rank: Frequent Contributor
timestamp: July 17, 2014, 01:14:59 pm
content: I will try this evening however because the two read differently I thought that it was more likely to be the MUX or the PIC rather than the DVM and as I have now replaced the MUX I am left with the PIC.

author: Andy Watson
author_rank: Super Contributor
timestamp: July 17, 2014, 01:21:38 pm
content: Quote from: alanb on July 17, 2014, 01:14:59 pmand the four voltage signals that the MUX switches between.

author: alanb
author_rank: Frequent Contributor
timestamp: July 17, 2014, 01:40:10 pm
content: Correct. Unfortunately I have been jumping to too many conclusions on this. I need to do some proper measurements and diagnosis. Hopefully I will have time tonight, if not I won't be able to work on it for another week.

author: WarSim
author_rank: Frequent Contributor
timestamp: July 17, 2014, 02:27:27 pm
content: I tried to buy some TTI power supplies. What I received was one crushed power supply I did not dare turn on, and a cheeper model in a box labeled as the more expensive model.I am still waiting for the results of a CAR to decide if it was a rare incident or not before considering ordering a TTI again.Sent from my iPad using Tapatalk

author: alanb
author_rank: Frequent Contributor
timestamp: July 17, 2014, 03:01:16 pm
content: Quote from: WarSim on July 17, 2014, 02:27:27 pmSounds like a problem with the person you are buying off rather than the products themselves. The reputation of TTI seems pretty good. I have no criticism of the one that I have purchased, it has a faulty meter but I am expecting that can be fixed fairly cheaply. Other than that fault it works well and it is over 20 years old.

author: WarSim
author_rank: Frequent Contributor
timestamp: July 17, 2014, 03:15:20 pm
content: The channel is Element14/Newark/Farnel. Somewhere the errors where made. Some where in the line the wrong part was put in a box labeled by TTI. Somewhere the item box was crushed so much that chassis was bent and the cover rivets popped. All the participant in this process have a good reputation. That is why I had a CAR started. This is two of the three errors made in this purchase process, don't worry there is plenty of blame to go around. I am not looking for someone to blame I just want to know why and give the error makers the chance to find a solution to keep it from happening again. Because I can wait for an answer before reordering I will.I will count the positive portion of your response as a vote of confidence for TTI.Sent from my iPad using Tapatalk