Partial Tear Down - MJ Research PTC-200 Thermal Cycler - Page 1
Forum section: electronics / general

author: mianchen
author_rank: Regular Contributor
timestamp: July 10, 2012, 04:18:19 pm
content: Polymerase chain reactionaka PCR is the basis of many modem molecular techniques.Thermal cycleris a piece of equipment used in molecular genetics/forensic laboratories etc to amplify a tiny quantity of DNA through PCR reactions, which are often multiplexed or paralleled in order to detect different known andde novomutations of genes. Precision temperature control is the key to PCR. A typical PCR 'cycle'consists of 3 temperature steps: 95°C - 60°C - 72°C. A full PCR run consists of many tens of these repeated cycles in order to obtain exponential 'amplification' of the initial DNA template. Temperature in each step is tweaked according to the application and the transition between different temperature steps has to be kept to minimal to get the best result. Also unlike most of test equipment, a thermal cycler in a busy laboratory is often running 24/7, especially in clinical diagnosis environment.MJ research in the US has made some of the most robust PCR equipment. Many of the MJ machines made in the 80s and 90s are still in service today. Unfortunately MJ went bust and taken over by a company - they never managed to make anything as good. Many of the new units keep failing after a year or even a few months of continuous use.I've not managed to completely take one apart due to various reasons, but I'd still like to share some photos with people here who's interested.

author: amyk
author_rank: Super Contributor
timestamp: July 11, 2012, 08:02:23 am
content: So it's essentially like a reflow oven, only smaller and at much lower temperatures.What is the failure reason for these units? It probably has something to do with the rapid continuous temperature changes.Other than that it looks quite simple and serviceable. A few comments/notes on the parts.-MC68HC11Kmain controller. Does not have (EEP)ROM (see below).-ADS7832BN4-channel 12-bit ADC. Might be for temperature sensing.- 2xBI 668-A-3241B3K24 precision resistor network, probably related to the ADC above- 2xAT28C6464Kbit parallel EEPROM. Firmware storage.-SN74HC574D-type flip-flops. For the user interface controls.-HD44780standard LCD controller.-HY6264A64Kbit SRAM. Probably stores nonvolatile settings backed by the little rechargeable battery located nearer the depths of the machine (wouldn't it have made more sense to put the battery in the corner for ease of access on replacement, instead of the chip itself?)- 72,000 uF of smoothing capacitance-MAX222RS-232 interface-SN75162BandSN75160BIEEE-488 bus transcievers.-NAT4882IEEE-488.2 controller chip.-AT29C0101Mbit flash. No idea what this could be for. More firmware?

author: SeanB
author_rank: Super Contributor
timestamp: July 11, 2012, 03:25:32 pm
content: I would guess fans that die, petlier coolers that need new heatsink compund, dust and capacitors that send off the switching transistors. Add dry joints on the big devices and you probably have all the faults.

author: mustafa67
author_rank: Newbie
timestamp: June 07, 2015, 07:52:29 am
content: Thank you for your replay.I have 2 device and inside the board there may be short cut.did you have any expreience about PTC 200 board draw?150 ohm resistandance in first part (220 volt region is normal), but after tranformer voltage is 150 and resistancve have 0 ohm. so there is a short cut in sistem.does it possible transistor sistem death?Quote from: amyk on July 11, 2012, 08:02:23 am